Analog TV shutdown commences in Mildura/Sunraysia in 1st half of 2010 and will be complete by 2013. Timetable

Before I get started,

New Zealand specific information is in Blue, Australian specific information is in Red.
Some receivers have a "switch" called "antenna power". Please leave it off. It is to power masthead amplifiers.
Most outdoor antennas will short this "antenna power" out. The receiver will limit the current to prevent a major failure, in most cases it will just waste electricity continuously, unless the receiver is unplugged at the wall.

Most masthead amplifiers in this country use a "power injector". This blocks any DC or low frequency signal going to the receiver. Thus the receiver is protected and the power. The power injectors are typically a low voltage AC. This prevents corrosion in the cabling. This injector must be in the power pass output of any passive splitter otherwise the masthead amplifier will not be powered.


All planning for the allocation of TV channels, coverage areas and polarisation is made by the Australian Communications and Media Authority (ACMA), Radio Spectrum Management

Channels
TV Bands
TV band 1 channels 0-2. 45-70 MHz
TV Band 2 Channels 3-5 85-108 MHz, yes, this includes the FM radio band
TV channel 5a was only used in Australia and is being phased out
TV band 3 channels 6-12, 174-230 MHz, includes VHF DAB+ Digital Radio
TV band 4 channels 27-35 519-582 MHz
TV band 4+ channels 27-50, 519-687 MHz
TV band 5 channels 36-69 582-820 MHz

Suggested UHF bands (To give equal output regardless of frequency (channel number)
X = Channels 27 - 40 (519 - 617 MHz)
Y = Channels 41 - 55 (617 - 722 MHz)
Z = Channels 56 - 69 (722 - 820 MHz)


Bands 1, 2 and channel 5A will not be used for digital TV anywhere in Australia.

Band 1 Channels 1-3 44 - 68 MHz Analog only
Band 3 Channels 4 -12 174-237 MHz DAB+ Digital radio Analog TV only

Suggested bands (To give equal output regardless of frequency (channel number)
X = Channels 27 - 35, 38 (518 - 618 MHz)
Y = Channels 39 - 50 (618 - 710 MHz)
Z = Channels 51 - 62 (710 - 806 MHz)
Scaled drawing including dimensions on page 1

Real Channel Numbers and Logical Channel Numbers
The receiving section of TV receivers work on the channel numbers indicated in TV Bands. If you wish to add an additional transmitter to repeat the program in an adjacent area you will have to use another channel, otherwise there will be interference between the signals. To use the same channel the transmitters must be at least 400 km apart. (Digital SFN are excepted. SFN is a Single Frequency Network which has repeaters on the same channel in the same coverage area. The signals from each transmitter must be made identical a point halfway between the transmitters. This does not work in analog.)

Since the metropolitan networks use their main transmitter's channel number as the network name (eg, 7, 9, 10) for digital TV they transmit a logical channel number This means that the receiver may be using channel 69 but the program name as displayed on the front of the STB may be 7 for example.
In installation the STB usually will show the real channel number, as well as the LCN.

Where there is a translator in the same coverage area as the main transmitter, the receiver may be able to receive both. One more reliably than the other. Since automatic channel scan usually starts at channel 6 and finishes at channel 69, the low channel numbers are given the LCNs. When the receiver detects the same LCN on another channel it may allocate it a LCN of between 350 and 399. This is what is displayed on the screen or the front of the STB. To fix this you have to select the LCN and then manually scan for the better signal.

Logical Channel Numbers (LCN)
The network is identified by the LH digit displayed on the front of the STB. It is also used by the remote control for channel selection.
1 = TEN Network
2 = ABC
3 = SBS
4 = Miscellaneous (including Datacasting)
5 = TEN affiliates (eg. Southern Cross)
6 = Seven affiliates (eg. Prime, GWN)
7 = Seven Network
8 = NINE affiliates (eg. WIN, NBN, Impaja)
All digital transmissions are capable of being split to carry multiple programs. (eg ABC and ABC2)

Polarisation
Drawings of both polarisations on different antenna types, pages 2 - 4
For maximum received signal strength the receiving antenna should be parallel to the one on the transmitter tower. In Australia we use both horizontal and vertical transmitting antennas. This means we can put two transmitters on the same channel much closer together that if we only used one polarisation. In some areas of Australia band 3 transmitters are vertically polarised and band 4 & 5 horizontal on the same transmitter tower. eg. Canberra and Wide Bay.

Particularly where vertical polarisation is used, the cabling between the antenna and the receiver must be well shielded otherwise the cable becomes a second antenna. The best cable for this is quad shielded RG6 cable, with F connectors on any "joins".

Dipole the Most Basic Antenna.
Dipole
This is the most fundamental antenna. This is your typical rabbit’s ears antenna with the metal rods folded out into a straight line. Its total length is related to the frequency to be received.
Length (mm) = 15 000/frequency (MHz). As examples for channel 0, (48.5 MHz) the antenna should be 3 metres long. Channel 6 (177.5 MHz) 842 mm, channel 69 (816.5 MHz) 183 mm. If the above formula is used it will be a maximum for that frequency.
The dipole has a figure of 8 directivity pattern, with the maximum sensitivity at right angles and in the same plane as the metal rods. End on it is not very sensitive. The front to back ratio is 0 dB or equally sensitive. If you look at the dipole end on it is omnidirectional.

The effect of the frequency or real channel number
It should be remembered that the gain is relative to a dipole at that frequency.

So if the field strength is 1 Volt/metre then a channel 6 (177.5 MHz) antenna has a dipole length of 0.842 m so the voltage from the dipole of this length tested at 177.5 MHz was 0.842 V.

Repeat this for channel 69 (816.5 MHz) the dipole length is 0.183 m. So its dipole output is 0.183 V with a 816.5 MHz signal.

So just by changing channels from 69 to 6 there is an of signal strength of 13 dB

So to get an antenna for channel 69 to give as much signal as one designed for channel 6 you need to add enough elements to increase the sensitivity of the antenna by 13 dB. Hence you pay for around the same amount of metal for the same voltage. It is just cut differently!

As a reminder there is usually an increase in power from the transmitter for the same coverage area of between 4 & 8 dB

As a result if you just use a dipole of the correct length and tested every channel the sensitivity varies by 2.4 dB with the least signal at channel 12.

Gain measured in dB
This is the logarithmic ratio of the signal power from the antenna under test to the signal power from a dipole at the test frequency. Usually, the bigger the better. This is usually achieved by focussing the signal on the dipole.

Height of the antenna above the ground. The closer you get to line of sight the better. Remember on long distances the earth is a sphere so the waves will have to bend over the horizon. Clearing trees and buildings and blocking terrain will have a dramatic effect. Also the higher the antenna the further it is from sources of impulse interference. Unfortunately the higher the antenna the longer the down lead will have to be. These cables have losses so there is an optimal height. This height depends on the channel in use, the cable characteristics and whether a masthead amplifier is being used to overcome the loss.

Antenna Types
The most common types in TV reception are
Yagi-Uda, Log Periodic and Phased Array See pages 2 - 4

Yagi-Uda
Hidetsugu Yagi, & Shintaro Uda invented the Yagi-Uda antenna in the Tohuku University, Japan, in 1926
This antenna has a dipole which is connected to the down lead via a balun. The dipole is commonly folded.
A reflector is placed on the side away from the transmitter to prevent signals from the back being received and to reflect any signals that got past the dipole.
Directors are placed parallel with the dipole to focus the electromagnetic waves on the dipole. The greater the number of directors the more sharply focused the antenna becomes and the stronger the signal. Remember using the sun through a magnifying glass lighting the paper!

The entire antenna is connected to earth except the dipole. A ferrite transformer is used to keep the dipole above earth (this is a balun), since the receiver end of the cable is likely to be earthed.

Log Periodic
This antenna was invented in the University of Illinois, USA in 1955
This antenna consists of cross connected dipoles. None of the antenna is earthed. It works by having a longer dipole behind acting as a short to signal from behind at that frequency. The dipole in front can have no function at all; act as a second dipole or as a director. This depends on the number of dipoles near that frequency. Since there are a large number of dipoles, a linear transformer is used to obtain the standard 75 ohm output to match the cable. Since the antenna must not be connected to earth either the whole antenna is not earthed or insulators are used on each dipole.

This antenna usually has a very good front to back ratio, and medium gain depending on the frequency range required and the number of dipoles.

An indoor Log Periodic Antenna is available. It should be used for UHF and be fed into the U section of a diplexer to remove interference for lower frequencies.

Phased Array
Assuming that all the other antennas are mounted horizontally, this antenna has an even number of dipoles mounted one above the other. Typically each of these dipoles is accompanied by a reflector. The vertical spacing is related to the frequency, as is the length of the dipoles. All of these antennas are earthed except the dipole.

Directivity in the horizontal direction is not great because there is only a dipole and a reflector. In the vertical direction the directivity is increased because of the stacking of the dipoles.

Quality of the signal

Carrier to noise ratio(c/n) usually measured in dB. It’s an indication of how strong the signal is compared to the noise. The noise may come from interference or the noise generated in an amplifier. This ratio can be improved by using a more directional antenna (One containing more elements)

The importance of this reading is that if the carrier and the noise are nearly equal, you have fallen over the digital cliff and you will see either no signal message or pixellation and sound plops.

Noise figure is the carrier to noise ratio at the output (dB) - carrier to noise ratio at the input of an amplifier. This figure for modern masthead amplifiers can be as low as 1 dB. This is how much worse the amplifier is making the carrier to noise ratio.

Bit Error Rate (BER) If the carrier to noise ratio is low, then there will be a large bit error rate. This can also be caused by reflected signals particularly those nearing the main signal's strength. This is where antenna design is important as is using an antenna which is directional enough.

Wave Propagation
Ideally signals used for DTV travel in straight lines, just like light. Light can be bent around objects and reflected.
So if you could use a telescope and see the top of the transmitter mast this is called "line of sight" and is a straight line. This gives the strongest signal, although the lower frequencies (real channel numbers" needs some clearance below this line (particularly half way between the transmitting and receiving antennas) for maximum signal. The best antenna type is a Yagi-Uda/Log Periodic for horizontal polarisation and a phased array for vertical.

If you use a powerful search light or the sun, you can usually see the light even though there is not a straight line between your eyes and the light source. This is because it will reject reflected signals from the sides of the antenna. This can be because of reflection or diffraction around an object. This object may be the earth. So if the signal is substantially diffraction, then you need to use the recommendations for a diffuse signal. This is a phased array for horizontal polarisation and Yagi-Uda/Log Periodic in vertical polarisation.

Lastly if the signals are travelling over 100 km or over substantial body of water, the temperature changes in the atmosphere, varies the density of the air. This causes the signals to bend either towards the earth or away from it. This is why some long distance reception occurs near cold fronts and at the end of summer days on the coast.

Comparison of Characteristics
Dipole: On its own is usually only used in indoor antennas and when bent into a near circle for boats. This is where we do not want directivity! These antennas are not very sensitive and some have in build amplifiers. The will pick up reflected signals and this gives ghosted images in analog and if it is bad enough will cause pixellation and sound plops. ie the Bit Error Rate (BER) will be high.

Yagi-Uda:They have a sensitivity which is related to the number of directors, but element for element, more gain in a restricted range of frequencies, the range widens as the frequency to be received increases. So for an antenna designed for channel 60 it will cover a greater range of channels than one at channel 6, all else being equal

It is less likely to receive lower frequencies from power line interference, car ignitions and high powered radio transmitters. This is because only the dipole is connected to the down lead.

Log Periodic:This antenna has less sensitivity but can maintain it over a wide range of frequencies. The gain is related to the range of frequencies and the number of dipoles.

Typical Log Periodic TV antennas designed for bands 3-5 cover this range as a complete coverage from 174 to 820 MHz plus. Since there is no TV channels between the top of channel 12 and the bottom of channel 28 this sensitivity is wasted on being sensitive to two way radio communications.

Phased Arrays:Since this antenna has better vertical directivity it is typically used for long distance and paths blocked by terrain and buildings. (Imagine looking at the sunset over the sea. What you see is a thin bright line on the horizon.) Reflected signals are usually not a problem in weak signals as they will be weaker.

Combined antennas: Your average bands 1-3, 4-5 antenna (Channels 2-12 + channels 28-69) consists of a Log periodic for bands 1-3 and a Yagi-Uda for bands 4 – 5.

Log periodics drop rapidly in sensitivity outside their design range which is why the older style combined antenna will not receive channels 11 & 12.

For Australian Digital TV no channel under channel 6 will be used so any sensitivity there makes you susceptible to interference causing pixellation and sound plops.

European Antennas
These are designed to receive channels 21-35. In Australia channels 21-26 are not used for TV but for communications including UHF CB radio. This 49 MHz is not only not required but can cause pixellation and sound plops if the interference is strong enough. Similarly their sensitivity extends past channel 68 making the antenna sensitive to mobile phones, which can also cause the above effects.

Vertically Polarised Signals
If reflected signals are a problem, phased arrays are better than Yagi-Udas and Log Periodics. If you want long distance or diffuse signals then multi element Yagi-Udas are the way to go.

Advertising
An element is a reflector, dipole or a director. All are mounted at right angles to the boom. I see advertised an SF91 antenna, if you look at a picture how many elements do you get? 22!

Impulse Interference
This causes the picture to break up and plops in the sound.

It is usually caused by switching of electrical devices in the house, dirty power line insulators (particularly after a long dry period then drizzle), petrol engines. This interference is picked up by the antenna and the cable to the receiver. Spikes on the mains cable are an unlikely cause. So spike suppressor power boards are usually ineffective.

Stopping this problem
Install an antenna according to your area. Geographic Viewers' Forums Then see Get the best reception. Which transmitter and which antenna
Use Quad shielded RG6 Coax cable and keep it away from electrical wiring. If it has to cross it keep it at right angles. Use F connectors.

The best way in areas where you still use analog channels 0-5A, 1-12 and/or FM, is to keep digital and analog wiring separate.

Areas which use Band 3 (Real channels 6-12)
Many of you have bought expensive antennas which are designed to receive channels 0-5A. If you are not using it for analog, then feed the antenna into a Bandpass Filter & triplexer.
If masthead amplifiers are being used see near the end of this post.

If band 3 is not used in your area, then get the correct UHF antenna and forget the paragraph above!

Separation of antennas on the mounting pole.
The theory is at least 1/2 wavelength separation. This would be around the length of the element which has the cable connected. If it is a log periodic, that will be the longest dipole.

All separations in the list below are in mm. For the lowest mounted antenna it is the roof particularly if it is metal.

Lowest edge of Band 3, Channel 6: 862
Lowest edge of Band 4, Channel 27: 288
Lowest edge of Band 5, Channel 35: 258

Channel 0: 3 333 mm
Channel 1: 2 679 3 410
Channel 2: 2 381
Channel 3: 1 765

FM radio: 1 714

If vertical polarisation is used I would double these figures.


Amplification
Masthead amplification is the best so that any signals picked up on the down lead is not amplified causing interference (pixellation and sound plops). They are necessary where there is low signal strength at the antenna and where long down lead is used. The cable loss depends on the cable length and the channel in use. Cable Loss Graph. Splitter amplifiers are required where more than 4 receivers/STB/Videos are used.

Amplifiers can make the situation worse. Where strong signals are amplified with weak ones the weak signal will have more interference than with no amplifier. This also occurs with a corroded antenna.

To assess overloading, use this technique prior to any amplification Measuring the real levels with a meter is much quicker and more exact.

Masthead Amplifier Overload

Any amplifier should be linear. This means the gain or amplification does not vary with the input signal voltage.

As the input signal voltage increases, at some point, the power supply voltage restricts the amplifier output. So you can get to the point where you may increase the input voltage for no change in the output. This is called overload, clipping or limiting.

There are two types of distortion which occur when the output is at or near limiting
• Harmonic distortion. If the input frequency is 1 kHz, then the output will contain 3, 5, 7… kHz. There can also be even harmonics, but they are usually less powerful.
• Intermodulation distortion. If the input contains 2 or more frequencies the following will occur. This example is for 2 kHz and 5 kHz
The output signal will contain;
f1 =2 kHz
f2-f1 = 5-2 = 3 kHz
f2 = 5 kHz
f1+f2 = 7 kHz
If more frequencies are present at the input every combination is produced.

These Effects on Masthead Amplifiers
Distortion in Masthead & splitter amplifiers along with the input to digital receivers will cause a poor Bit Error Rate.
Harmonic Distortion
There are two effects.
• The most important is that impulse interference can be the same voltage or larger than the TV signal. The harmonic distortion will produce huge numbers of harmonics, some of which will be in the frequency range of the TV signals you wish to watch. In digital this causes pixellation and sound breakup.
• Harmonics of one channel can affect another the worst case is channel 2’s harmonic is on channel 8. This can occur for all mainland capitals on Nine digital, and in Hobart on ABC digital. Other combinations are;
channel 5 analog to 9A digital
channel 7 to channel 30
channel 8 to channel 33
channel 9 to channel 36
channel 9A to channel 39
channel 10 to channel 42
channel 11 to channel 45
channel 12 to channel 48
In analog harmonic distortion causes the windscreen wiper effect, in digital unstable reception similar to the above.

Inter-modulation Distortion
The greater the number of high level signals the more chance there is for interaction. This is because the combinations of sum and difference frequencies will occur between all frequencies present. This is the reason Master Antenna Distribution Amplifiers have a single amplifier for each TV signal. This effect can only occur in amplification and modulation. So, the outputs of the channel amplifiers in the distribution system are just combined together with no additional distortion prior to distribution.

Minimising these problems.
• The higher the gain the greater the problem particularly if the signal strength at the input changes with the weather etc.
• Remove impulse interference prior to amplification so that it will not be added to the signal.
• Use antennas tuned to the frequencies of the stations you wish to view.
• Use quad shielded cable, a shielded amplifier box and keep this box at least a metre from any antenna.

Geographic Viewers' Forums Then see Get the best reception. Which transmitter and which antenna for the recommended antennas and amplifiers for your area.

Masthead Amplifier Survey

Difficult installations.
I have recommended a single masthead amplifier in the above posts. Where the signals are very weak, and more than one band is used you can get more gain by using two amplifiers at twice the price!

New Zealanders:
For DTV the only current masthead amplfiers you should use is Band 5 types for NZ channels 38 - 62 where possible or UHF amplifiers only otherwise.

For example 1
band 3 and 4(+)
Band 3
Kingray MHV44HLG Its gains are B3 44 dB B4-5 10 dB Feed the B3 antenna into the V input
Band 4 & 4+
Kingray MHU44G The gains are B1-3 -1 dB, B4-5 44 dB
Feed the B4 or 4+ antenna into the U input. The next choice is to feed the output of the B3 amplifier into the V input of this amplifier. You get more gain the other way around, but 54 dB is a huge gain.

Example 2
band 3 and 5
Kingray MHV44HLG Its gains are B3 44 dB B4-5 10 dB Feed the B3 antenna into the V input
Band 5
Kingray MHU44B5G B1-3 -1 dB, B5 44 dB
Feed the B5 antenna into the U input. The next choice is to feed the output of the B3 amplifier into the V input of this amplifier. You get more gain the other way around, but 54 dB is a huge gain.

In both cases the power is supplied from a PSK08 on a receiver end of the down lead. There is a link to allow the power to be fed through the B4 or B5 amplifier to the B3 amplifier. Check the instructions. Also remove the link connecting the V & U inputs together.

Splitting Signals

Losses are like this
2 outlet 3 dB
3 outlet 5 dB
4 outlet 6 dB
5 outlet 7 dB
6 outlet 8 dB
7 outlet 8 dB
8 outlet 9 dB
These are theoretical losses. Actual losses will be greater than this by a few dB depending on if it is VHF or UHF.

Masthead amplifers should not be used, use an amplified splitter instead. The difference is that amplified splitters have a gain of around 10 dB which matches the sort of losses shown above. Masthead amplifiers are designed for very small voltages where as splitting ampllifiers are designed for larger voltages so overloading is much less likely.

The signal strength display is not linear so half the signal will only produce a small drop. All receivers have automatic gain controls which are logarithmic as the list of dBs is.

Provided each outlet has a receiver or terminator plugged in, which is the assumption in the second point, and the resulting signal strength is high enough you will not see any difference. You should look when it is raining and switch on some electrical appliances such as fluro lights, and devices with motors in them.

Lastly most receivers have an antenna input and an RF output. I would use this output to feed the next card as the losses in the split are usually amplified by that amount of loss.

Faultfinding

Bit Error Rates of more frequent than 1 error in every 10 000 bits, cannot guarantee pixellation and chirp free reception.

This BER indicates the amount of errors found in the signal from the transmitter. The signal contains extra data for error detection and correction. This measurement in receivers is often called quality.

The problem is if the error rate is too high what is causing it?

The usual causes are;
1. Insufficient signal or excessive noise.
2. Delayed signals from either reflections or another SFN transmitter.
3. Additional signals from either impulse interference or intermodulation occurring in overloaded Masthead amplifiers or corrosion in the antenna.
4. Antenna corrosion Affected channels are
Channel 2 analog to channel 8
channel 5 analog to 9A
channel 7 to channel 30
channel 8 to channel 33
channel 9 to channel 36
channel 9A to channel 39
channel 10 to channel 42
channel 11 to channel 45
channel 12 to channel 48



How do you separate these factors?

1. The carrier to noise ratio (measured in dB) if this ratio is low then you need more signal from the transmitter. This can be achieved by one or more of the following methods.

• Increase or vary the elevation of the antenna, change the antenna location.
  
• Ensure the antenna design channel range matches that of the channels being used.
  
• Minimise the loss from the antenna to the receiver through the use of the shortest low loss cable.
  
• Increase the directivity of the antenna to focus more signal onto its dipole.
  
• For longer distances you need to increase the capture area by reducing the vertical acceptance angle and keeping a horizontal acceptance angle. (Think of a sunset as a thin horizontal line on the horizon).
  
• Use a masthead amplifier to overcome cable losses.

2. A more focussed antenna (one with more elements is required). The amount of focussing is its "gain" in dB. A high front to back ratio may be required if you are on a line between the two SFN transmitters.

3. To reduce the level of impulse interference which will give sporadic high BER and low C/N readings, the following will help.

• Use quad shielded RG6 cable and F connectors.
  
• Ensure the antenna is only designed to receive the channels in use. Therefore in Australia no antennas designed to receive channels 0-5A
  
• If a masthead amplifier is used it must have a filter on its input to pass only the channels of interest, otherwise the impulse interference will get worse.
  
• In severe cases a 160 MHz high pass filter and even a braid breaker can be used at the receiver to minimise the interference picked up on the cable. This is also useful where AM, FM, two way radios, CB and amateur radio transmitters give trouble.
  
• Where some channels are much stronger than others or all signals are strong, the gain of any masthead amplifier must be reduced because you will get interfering signals in the channels you really want.
  
  Identify the source of impulse interference The AM radio technique can also be used for identifying cracked high voltage insulators on power lines in the street.
  
• So if you get a high BER and a low C/N you need to get more signal, if C/N is high and the BER is poor then look at points 2 & 3. Point 3 is likely to cause rapid variations in BER and C/N.

Note. The signal strength reading on STBs and cards is a measure of the Automatic Gain Control signal. This signal does not have a linear relationship between the strength and the reading. Also it is not calibrated. Measuring meters are calibrated!

Is there a digital antenna as opposed to an analog antenna?

Analog

• Vision uses vestigial sideband and a pair of FM modulated carriers for Sound. Colouring signals are double sideband suppressed carrier.
  
• So as the signal strength goes down you get more noise appearing as dots and the sound is generally unaffected until it drops out of limiting.
  
• So for vision there is a gradual reduction in quality as compared to signal strength.
  
• Secondly any reflected signals will appear to the left of the original signal so antenna directivity is used to remove these ghosts.
  
• Impulse noise appears as rows of dots with the sound generally unaffected.

Digital

• DVB-T uses 1705 of carriers spread over the 7 MHz bandwidth. This is the same bandwidth used for analog. It is like using parallel data, one carrier per bit.
  
• Digital uses channels adjacent to analog ones, this includes high power transmitters. You cannot use adjacent analog channels because the interference is horrific. Digital receivers can reject the analog signals, but the analog TVs cannot. So digital is transmitted at a quarter of the power of the analog transmitters to prevent interference to analog signals.
  
• Some interference and noise rejection is achieved by limiting the number of discrete levels which need to be received. In digital it is a maximum of 32 in analog it could be infinite but is usually limited to a range of 10000:1 for good pictures. However, since the information is more densely packed, the visual and auditory effect is much greater if the interference or noise is detected by the receiver. There is a limited amount of error correction. Hence the "digital cliff". This where the signal strength into the receiver keeps dropping. There will be no effect on the superb quality until it suddenly pixellates as mentioned in the next paragraph.
  
• If impulse noise is added to a digital signal errors occur, the will cause pixellation (picture breaks up in to blocks and either a gap in sound or a squawk).

The effect of the above on antenna design

• Since the amplitude of impulse noise from sparking in switches, power lines etc increases as the frequency decreases the ACMA has decreed that there will be no digital transmitters below 174 MHz (Channel 6) So your antenna should not be designed like many are to receive from 45 to 144 MHz (channel 0-5A) They pick up interference well and that metal work could be used to increase gain in the required channels above channel 5A.
  
• Without signals below 174 MHz, masthead amplifiers can be set to a higher gain particularly if they have a bandpass filter in their inputs. Then it will only amplify the wanted signal and not overload on unwanted signals. This cause intermodulation distortion and interfere with the wanted signals.
  
• As in good telecommunications practice you should use an antenna which is designed to cover the frequency range in use. This varies all over the country so see “Get the best reception. Which transmitter and which antenna” in the geographic forums at the bottom of the home page of the main forum.
  
• Digital ready antennas are typically advertised in areas where digital is using channel 11 & 12 which is all capital cities (except Canberra and Darwin). These channels have been added since digital. So what has happened is that a lot of digital ready antennas are designed from channels 1-12,+ 28-35. These antennas are not ideal. Some add an F connector for a more reliable connection with less reflections.
  
• Antenna gain is a issue because of the lower transmitted power and the pick up of impulse noise not only in the antenna but also in the down lead. Remember the effect of some impulse noise on analog TV is usually some intermittent or continuous rows of dots. So as long as the signal to noise ratio is adequate impulse noise will not be seen.
  
• They are usually quite small on the screen. There is no effect on the sound. In digital the picture breaks up into much larger squares and the sound either is muted or produces a loud screech. You miss an important part of the plot!
  
• Directivity may or may not be an issue. Since many carriers are used this makes each pulse longer. So short term reflected signals can be ignored by the receiver. Decoding will be perfect.
  The ACMA is now specifying Single Frequency Networks (SFN) in some areas of Sydney, Central Coast NSW, Newcastle, Melbourne, Gold Coast, Sunshine Coast and Cairns.
  
• Lastly the ACMA has to make duplicates of all analog transmitters in digital and not use channels 0-5A. This can mean different antennas are required. Sometimes the polarisation changes as well. There are also a number of high powered sites using vertical polarisation for VHF and horizontal polarisation for UHF.
  
• If you take the Darling Downs as an example all stations are in band 4+ (channel 28-50) with Southern Cross on channel 0. This antenna should be removed when converting to digital. In Toowoomba, all stations are in band 5 so no antenna changes should be required provided the installation is in good condition. The ACMA has tried to allocate digital channels in the same band as analog ones so that a minimum number of households have to buy new antennas.
  
• So yes there can be differences between digital and analog antennas particularly at VHF.
  
• Questions on this post should be in this strand.

Additional information
hdtvprimer.com/ANTENNAS/basics

Australian Conversions

Antenna Basics

A TV channel in Australia will always occupy 7 MHz of this spectrum. For digital TV this is
Band 3 Channels 6-12, 174-230 MHz,
Band 4 Channels 27-35, 519-582 MHz
Band 4+ Channels 28-50, 526-687 MHz
Band 5 Channels 36-69, 582-820 MHz

“RG-6 will lose 1 dB of the signal every 18 feet at channel 52” 1dB for every 5.5 m at 700 MHz which is at our channel 52. This author recommends a mast-mounted amplifier whenever the cable length exceeds 6 m.

Cable losses graph is per 30 m.

“When the cable run is longer than 200 feet, the low-numbered channels can become too strong relative to the high-numbered channels.” 200 feet = 60 m. Masthead amplifiers are recommended on my “Get the Best Reception” posts use input filters for the channels used in that viewing area which can overcome this problem.

If you wish to use those staples they are 14 mm wide.

Distribution amplifier used when the cable is more than 45 m

For DTV in Australia, as long as the antenna is designed for band 3 or above an FM filter should only be required close to FM stations. You would be better off with a 174 MHz high pass filter and cut FM and most other interference out.

The NEC requirements do not apply here use the SAA Wiring Rules AS/NZS 3000:2007 and state legislation. Our TVs do not earth the antenna input into the tuner as most equipment is double insulated and earth is not connected at all.

Common TV Antenna Types
“A UHF Yagi today is designed for channel 69. If you see an old Yagi, it might be intended for channel 82. In the future they will be cut for channel 51.”

Channel 69 is 800 – 806 MHz which is approximately our channel 67.
Channel 82 is 884 MHz which is in mobile phone territory (including Next G) in Australia and probably the US.
Channel 51 is 692-698 MHz which is about our channel 52
The highest US channel is now channel 69 where as we go to 820 MHz, which is the top edge of channel 69.

AlanH

Then whats BAND 5

TV Bands
TV band 1 channels 0-2. 45-70 MHz
TV Band 2 Channels 3-5 85-108 MHz, yes this includes the FM radio band
TV channel 5a was only used in Australia and is being phased out
TV band 3 channels 6-12, 174-230 MHz, includes VHF trial radio DAB
TV band 4 channels 28-35 526-582 MHz
TV band 4+ channels 28-50, 526-687 MHz
TV band 5 channels 36-69 582-820 MHz

Bands 1,2 and channel 5A will not be used for digital TV anywhere in Australia.


AlanH

AlanH,

That was a good intoduction to antennas,informative but not too technical.

Cheers, C.M

All,
The reason I check which RF channels are to be used in a particular installation is to get the antenna which matches the channels.

The reasons for this are;
that the antenna size for size will give more signal on those channels.

to reduce the possibility of interference.

This reduces the chances of pixellation and sound plops.

Interference: For example no station in Australia will use a channel below channel 6 because the Australian Broadcasting Authority recognises that interference from power mains and car ignitions increases as the channel number is reduced. There is also 2 way radio communications between channel 5a and channel 6 High powered FM radio transmitters in channels 3-5

Channels 21-27 are used for communications including UHF CB

Just above channel 69 there is paging transmitters and mobile phones.

The only advantage of wideband antennas (eg Channel 6-69 and to a lesser extent channel 21-69) is that you do not have to change the type when you move. They are good for mobile applications.

AlanH

Hi AlanH,

thanks for the very informative read - though I have one regarding antennas for laptops:

what should be the minimum element length for the 'most useful' coverage, for a monopole antenna DVB-T?

and I guess the follow-up to that would be - can you recommend any brands/models for laptop users?

Thank you very much for any info on this.

Regards,
Gizmomelb

Gizmomelbourne,
On the end of each Get the best reception
Which transmitter and which antenna http://www.dtvforum.info/index.php?showtopic=12503
The required length depends on the channel to be received. Fortunately in Australia the lowest channel number is channel 6 745 mm, down to 215 mm for band 5. So it will have to be telescopic. It also needs to be either horizontal or vertical depending on the transmitter.

It needs to be remembered that the internal electronics of the computer radiates signals in the TV bands causing interference particularly when signals are weak. So it would be better to plug in an antenna.

AlanH

Hi
Just wondering if you have anymore detailed information on master head
amps in response to digital reception on band 5. Interested to find out
more information on better brands of amps and the total amount of ampliflication
allowed before pictures play up. Also doubling amps up is that sucessful
please let my know thanks
Matty

Matty,
Sorry for the delay because I must have missed your post.
For Band 5 I recommend Band 5
Kingray MHU44B5G with its Power supply PSK08
Kingray
It has two inputs a B1-3 (VHF input which has a very slight loss of -1 dB, the Band 5 input has up to 44 dB gain. This means it increases the voltage by a maximum of 159 times. So the input voltage must be small otherwise the output will overload. The advantage of this amplifier is that it only amplifies band 5 because it has in input filter.

If you need band 4 & 5 then use the MHU44G.

AlanH

Hey Alan

any chance of you dropping up to Gympie (under the Sunshine Coast section in Qld) to put up me new antenna......?

hehe...

I can't even work out which way to point mine......


Fingers.

Fingers,
I do not live anywhere near you. However, if you give me the name of the suburb in which you live I will give you the direction to point your antenna.

AlanH

:ph34r: Dear mr AlanH
I live in Perth (Connolly) and have read your extensive information about antenna,s.
Being 65 + it goes a bit over my head.
Could you recommend an antenna man in the Perth area who knows all those things you write about and could give me advice and possible install the best antenna for my area ?

Regards
Ewoud

QUOTE (alanh @ Dec 16 2004, 12:34 AM)

[size=7]Channels
TV Bands
TV band 1 channels 0-2. 45-70 MHz
TV Band 2 Channels 3-5 85-108 MHz, yes, this includes the FM radio band
TV channel 5a was only used in Australia and is being phased out
TV band 3 channels 6-12, 174-230 MHz, includes VHF trial radio DAB
TV band 4 channels 28-35 526-582 MHz
TV band 4+ channels 28-50, 526-687 MHz
TV band 5 channels 36-69 582-820 MHz

Bands 1,2 and channel 5A will not be used for digital TV anywhere in Australia.

Real Channel Number and Logical Channel Numbers
The receiving section of TV receivers work on the channel numbers indicated in TV Bands. If you wish to add an additional transmitter to repeat the program in an adjacent area you will have to use another channel, otherwise there will be interference between the signals. To use the same channel the transmitters must be at least 400 km apart. (Digital SFN excepted. SFN is a Single Frequency Network which has repeaters on the same channel in the same coverage area. The signals frome each transmitter must be made identical a point halfway between the transmitters. Does not work in analog.)

Since the metropolitan networks use their main transmitter's channel number as the network name (eg, 7,9,10) for digital TV they transmit a logical channel number This means that the receiver may be using channel 69 but the program name as displayed on the front of the STB may be 7 for example.
In installation the STB usually will show the real channel number, as well as the LCN

Logical Channel Numbers LCN
The network is identified by the LH digit displayed on the front of the STB. It is also used by the remote control for channel selection.
1 = TEN Network
2 = ABC
3 = SBS
4 = Miscellaneous (including Datacasting)
5 = TEN affiliates (eg. Southern Cross)
6 = Seven affiliates (eg. Prime, GWN)
7 = Seven Network
8 = NINE affiliates (eg. WIN, NBN, Impaja)

All digital transmissions are capable of being split to carry multiple programs. (eg ABC and ABC2)

Polarisation
For maximum received signal strength the receiving antenna should be parallel to the one on the transmitter tower. In Australia we use both horizontal and vertical transmitting antennas. This means we can put two transmitters on the same channel much closer together that if we only used one polarisation. In some areas of Australia band 3 transmitters are vertically polarised and band 4 & 5 horizontal on the same transmitter tower. eg. Canberra and Wide Bay.

Dipole the Most Basic Antenna.
Dipole
This is the most fundamental antenna. This is your typical rabbit’s ears antenna with the metal rods folded out into a straight line. Its total length is related to the frequency to be received.
Length (mm) = 15 000/frequency (MHz). As examples for channel 0, (48.5 MHz) the antenna should be 3 metres long. Channel 6 (177.5 MHz) 842 mm, channel 69 (816.5 MHz) 183 mm. If the above formula is used it will be a maximum for that frequency.
The dipole has a figure of 8 directivity pattern, with the maximum sensitivity at right angles and in the same plane as the metal rods. End on it is not very sensitive. The front to back ratio is 0 dB or equally sensitive. If you look at the dipole end on it is omnidirectional.

The effect of the frequency or real channel number
It should be remembered that the gain is relative to a dipole at that frequency.

So if the field strength is 1 Volt/metre then a channel 6 (177.5 MHz) antenna has a dipole length of 0.842 m so the voltage from the dipole of this length tested at 177.5 MHz was 0.842 V.

Repeat this for channel 69 (816.5 MHz) the dipole length is 0.183 m. So its dipole output is 0.183 V with a 816.5 MHz signal.

So just by changing channels from 69 to 6 there is an of signal strength of  13 dB

So to get an antenna for channel 69 to give as much signal as one designed for channel 6 you need to add enough elements to increase the sensitivity of the antenna by 13 dB. Hence you pay for around the same amount of metal for the same voltage. It is just cut differently!

As a reminder there is usually an increase in power from the transmitter for the same coverage area of between 4 & 8 dB

Gain measured in dB
This is the logarithmic ratio of the signal power from the antenna under test to the signal power from a dipole at the test frequency. Usually the bigger the better. This is usually achieved by focussing the signal on the dipole.

Antenna Types
The most common types in TV reception are
Yagi, Log Periodic and Phased Array

Yagi
This antenna has a dipole which is connected to the down lead via a balun. The dipole is commonly folded.
A reflector is placed on the side away from the transmitter to prevent signals from the back being received and to reflect any signals that got past the dipole.
Directors are placed parallel with the dipole to focus the electromagnetic waves on the dipole. The greater the number of directors the more sharply focused the antenna becomes and the stronger the signal. Remember using the sun through a magnifying glass lighting the paper!

The entire antenna is connected to earth except the dipole. A ferrite transformer is used to keep the dipole above earth (this is a balun), since the receiver end of the cable is likely to be earthed.

Log Periodic
This antenna consists of cross connected dipoles. None of the antenna is earthed. It works by having a longer dipole behind acting as a short to signal from behind at that frequency. The dipole in front can have no function at all; act as a second dipole or as a director. This depends on the number of dipoles near that frequency. Since there are a large number of dipoles a linear transformer is used to obtain the standard 75 ohm output to match the cable. Since the antenna must not be connected to earth either the whole antenna is not earthed or insulators are used on each dipole.

This antenna usually has a very good front to back ratio, and medium gain depending on the frequency range required and the number of dipoles.

Phased Array
Assuming that all the other antennas are mounted horizontally, this antenna has an even number of dipoles mounted one above the other. Typically each of these dipoles is accompanied by a reflector. The vertical spacing is related to the frequency, as is the length of the dipoles. All of these antennas are earthed except the dipole.

Directivity in the horizontal direction is not great because there is only a dipole and a reflector. In the vertical direction the directivity is increased because of the stacking of the dipoles.

Quality of the signal

Carrier to noise ratio(c/n) usually measured in dB. I an indication of how strong the signal is compared to the noise. The noise may come from interference or the noise generated in an amplifier. This ratio can be improved by using a more directional antenna (One containing more elements)

The importance of this reading is that if the carrier and the noise are nearly equal, you have fallen over the digitial cliff and you will see either no signal message or pixellation and sound plops.

Noise figure is the carrier to noise ratio at the output (dB) - carrier to oise ratio at the input of an amplifier. This figure for modern masthead amplifiers can be as low as 1 dB. This is how much worse the amplifier is making the carrier to noise ratio.

Bit Error Rate If the carrier to noise ratio is low, then there will be a large bit error rate. This can also be caused by reflected signals particularly those nearing the main signal's strength. This is where antenna design is important as is using an antenna which is directional enough.

Comparison of Characteristics
Dipole: On its own is usually only used in indoor antennas and when bent into a near circle for boats. This is where we do not want directivity! These antennas are not very sensitive and some have in build amplifiers. The will pick up reflected signals and this gives ghosted images in analog and if it is bad enough will cause pixellation and sound plops. ie the Bit Error Rate (BER) will be high.

Yagi:They have a sensitivity which is related to the number of directors, but element for element more gain in a restricted range of frequencies, the range widens as the frequency to be received increases.

It is less likely to receive lower frequencies from power line interference, car ignitions and high powered radio transmitters. This is because only the dipole is connected to the down lead.

Log Periodic:This antenna has less sensitivity but can maintain it over a wide range of frequencies. The gain is related to the range of frequencies and the number of dipoles.

Phased Arrays:Since this antenna has better vertical directivity it is typically used for long distance and paths blocked by terrain and buildings. (Imagine looking at the sunset over the sea. What you see is a thin bright line on the horizon.) Reflected signals are usually not a problem in weak signals as they will be weaker.

Combined antennas: Your average bands 1-3, 4-5 antenna (Channels 2-12 + channels 28-69) consists of a Log periodic for bands 1-3 and a Yagi for bands 4 – 5.

Log periodics drop rapidly in sensitivity outside their design range which is why the older style combined antenna will not receive channels 11 & 12.

For Australian Digital TV no channel under channel 6 will be used so any sensitivity there makes you susceptible to interference causing pixellation and sound plops.

Band 4 European Antennas
These are designed to receive channels 21-35. In Australia channels 21-27 are not used for TV but for communications including UHF CB radio. This 56 MHz is not only not required but can cause pixellation and sound plops if the interference is strong enough.

Vertically Polarised Signals
If reflected signals are a problem, phased arrays are better than Yagis and Log Periodics. If you want long distance or diffuse signals then multi element Yagis are the way to go.

Advertising
An element is a reflector, dipole or a director. All are mounted at right angles to the boom. I see advertised an SF91 antenna, if you look at a picture how many elements do you get? 22!

Impulse Interference
This causes the picture to break up and plops in the sound.

It is usually caused by switching of electrical devices in the house, dirty powerline insulators (particularly after a long dry period then drizzle), petrol engines. This interference is picked up by the antenna, and the cable to the receiver. Spikes on the mains cable are an unlikely cause. So spike suppressor powerboards are usually ineffective.

Stopping this problem
Install an antenna according to your area. Geographic Viewers' Forums Then see Get the best reception. Which transmitter and which antenna
Use Quad shielded Coax cable and keep it away from electrical wiring. If it has to cross it keep it at right angles. Use F connectors.

The best way in areas where you still use analog channels 0-5A, is to keep digital and analog wiring separate.

Areas which use Band 3 (Real channels 6-12)
Many of you have bought expensive antennas which are designed to receive channels 0-5A. If you are not using it for analog, then feed the antenna into a GME Kingray TF160 High Pass Filter. You will have to purchase a cover as well.

If masthead amplifiers are being used see near the end of this post.

If band 3 is not used in your area, then get the correct UHF antenna and forget the paragraph above!
Separation of antennas on the mounting pole.
The theory is at least 1/2 wavelength separation. This would be  around the length of the element which has the cable connected. If it is a log periodic, that will be the longest dipole.

All separations in the list below are in mm. For the lowest mounted antenna it is the roof particularly if it is metal.

Lowest edge of Band 3, Channel 6: 862
Lowest edge of Band 4, Channel 28:  285
Lowest egge of Band 5, Channel 35: 258

Channel 0: 3 333 mm
Channel 1: 2 679
Channel 2: 2 381
Channel 3: 1 765

FM radio: 1 714

If vertical polarisation is used I would double these figures.


Amplification
Masthead amplification is the best so that any signals picked up on the downlead is not amplified causing interference (pixellation and sound plops). They are necessary where there is low signal strength at the antenna and where long downlead is used. Splitter amplifiers are required where more than 4 receivers/STB/Videos are used.

Amplifiers can make the situation worse. Where strong signals are amplified with weak ones the weak signal will have more interference than with no amplifier. This also occurs with a corroded antenna.

To overcome the amplifier problem, the solution is to use only antennas designed for the range of channels required and to use an input filter to reject unwanted signals. Lastly the amount of amplifier gain may need to be reduced to prevent overloading.

Geographic Viewers' Forums Then see Get the best reception. Which transmitter and which antenna
for the recommended antennas and amplifiers for your area.

Difficult installations.
I have recommended a single masthead amplifier in the above posts. Where the signals are very weak, and more than one band is used you can get more gain by using two amplifiers at twice the price!

For example 1
band 3 and 4(+)
Band 3
Kingray MHV44HLG  The gains are B3 44 dB B4-5 10 dB Feed the B3 antenna into the V input
Band 4 & 4+
Kingray MHU44G The gains are B1-3 -1 dB, B4-5 44 dB
Feed the B4 or 4+ antenna into the U input. The next choice is to feed the output of the B3 amplifier into the V input of this amplifier. You get more gain the other way around, but 54 dB is a huge gain.

Example 2
band 3 and 5
Kingray MHV44HLG  The gains are B3 44 dB B4-5 10 dB Feed the B3 antenna into the V input
Band 5
Kingray MHU44B5G B1-3 -1 dB, B5 44 dB
Feed the B5 antenna into the U input. The next choice is to feed the output of the B3 amplifier into the V input of this amplifier. You get more gain the other way around, but 54 dB is a huge gain.

In both cases the power is supplied from a PSK08 on a receiver end of the downlead. There is a link to allow the power to be fed through the B4 or B5 amplifier to the B3 amplifier. Check the instructions. Also remove the link connecting the V & U inputs together.

Faultfinding

Bit Error Rates of more frequent than 1 e-4 cannot guarantee pixellation and chirp free reception.

This BER indicates the amount of errors found in the signal from the transmitter. The signal contains extra data for error detection and correction. This measurement in receivers is often called quality.

The problem is if the error rate is too high what is causing it?

The usual causes are;
1. Insufficient signal or excessive noise.
2. Delayed signals from either reflections or another SFN transmitter.
3. Additional signals from either impulse interference or intermodulation occuring in overloaded Masthead amplifiers or corrosion in the antenna.

How do you separate these factors.

1. The carrier to noise ratio (measured in dB) if this ratio is low then you need more signal from the transmitter. This can be achieved by one or more of the following methods.

Increase or vary the elevation of the antenna, change the antenna location.

Ensure the antenna design channel range matches that of the channels being used.

Minimise the loss from the antenna to the receiver through the use of the shortest low loss cable.

Increase the directivity of the antenna to focus more signal onto its dipole.

For longer distances you need to increase the capture area by reducing the vertical acceptance angle and and keeping a horizontal acceptance angle. (Think of a sunset as a thin horizontal line on the horizon).

Use a masthead amplifier to overcome cable losses.

2. A more focussed antenna (one with more elements is required). The amount of focussing is its "gain" in dB. A high front to back ratio may be required if you are on a line between the two SFN transmitters.

3. To reduce the level of impulse interference which will give sporadic high BER and low C/N readings, the following will help.

Use quad shielded RG6 cable and F connectors.

Ensure the antenna is only designed to receive the channels in use. Therefore in Australia no antennas designed to receive channels 0-5A

If a masthead amplifier is used it must have a filter on its input to pass only the channels of interest, otherwise the impulse interference will get worse.

In severe cases a 160 MHz high pass filter and even a braid breaker can be used at the receiver to minimise the interference picked up on the cable. This is also useful where AM, FM, two way radios, CB and amateur radio transmitters give trouble.

Where some channels are much stronger than others or all signals are strong, the gain of any masthead amplifer must be reduced because you will get interfering signals in the channels you really want.

So if you get a high BER and a low C/N you need to get more signal if C/N is high and the BER is poor then look at points 2 & 3. Point 3 is likely to cause rapid variations in BER and C/N

Note. The signal strength reading on STBs and cards is a measure of the Automatic Gain Control signal. This signal does not have a linear relationship  between the strength and the reading. Also it is not calibrated. Measuring meters are calibrated!

Is there a digital antenna as opposed to an analog antenna?

Analog
Vision uses vestigial sideband and a pair of FM modulated carriers for Sound. Colouring signals are double sideband suppressed carrier.

So as the signal strength goes down you get more noise appearing as dots and the sound is generally unaffected until it drops out of limiting.

So for vision there is a gradual reduction in quality as compared to signal strength.

Secondly any reflected signals will appear to the left of the original signal so antenna directivity is used to remove these ghosts.

Impulse noise appears as rows of dots with the sound generally unaffected.

Digital
DVB-T uses 1705 of carriers spread over the 7 MHz bandwidth. This is the same bandwidth used for analog. It is like using parallel data, one carrier per bit.

Digital uses channels adjacent to analog ones, this includes high power transmitters. You cannot use adjacent analog channels because the interference is horrific. Digital receivers can reject the analog signals, but the analog TVs cannot. So digital is transmitted at a quarter of the power of the analog transmitters to prevent interference to analog signals.

Since the digital signal consists of 2 states, on or off, the signal can be limited like in FM. So you can just look for transitions at the half amplitude point. This means that as the signal level reduces there is no effect of the program quality until the demodulator comes out of limiting. The error correction will help to remove some errors.

If impulse noise is added to a digital signal errors occur, the will cause pixellation (picture breaks up in to blocks and either a gap in sound or a squark).
The effect of the above on antenna design
Since the amplitude of impulse noise from sparking in switches, power lines etc increases as the frequency decreases the Australian Broadcasting Authority has decreed that there will be no digital transmitters below 174 MHz (Channel 6) So your antenna should not be designed like many are to receive from 45 to 144 MHz (channel 0-5A) They pick up interference well and that metal work could be used to increase gain in the required channels above channel 5A.

Without signals below 174 MHz, masthead amplifiers can be set to a higher gain particularly if they have a bandpass filter in their inputs. Then it will only amplify the wanted signal and not overload on unwanted signals. This cause intermodulation distortion and interfere with the wanted signals.

As in good telecommunications practice you should use an antenna which is designed to cover the frequency range in use. This varies all over the country so see Get the best reception. Which transmitter and which antenna in the geographic forums at the bottom of the home page of the main forum.

Digital ready antennas are typically advertised in areas where digital is using channel 11 & 12 which is all capital cities (except Canberra and Darwin). These channels have been added since digital. So what has happened is that a lot of digital ready antennas are designed from channels 1-12,+ 28-35. These antennas are not ideal. Some add an F connector for a more reliable connection with less reflections.

Antenna gain is a issue because of the lower transmitted power and the pick up of impulse noise not only in the antenna but also in the downlead. Remember the effect of some impulse noise on analog TV is usually some intermittent or continuous rows of dots. So as long as the signal to noise ratio is adequate impulse noise will not be seen.

They are usually quite small on the screen. There is no effect on the sound. In digital the picture breaks up into much larger squares and the sound either is muted or produces a loud screech. You miss an important part of the plot!

Directivity may or may not be an issue. Since many carriers are used this makes each pulse longer. So short term reflected signals can be ignored by the receiver. Decoding will be perfect.
The ABA is now specifying Single Frequency Networks (SFN) in some areas of Sydney, Central Coast NSW, Newcastle, Melbourne, Gold Coast and Sunshine Coast.

Lastly the ABA has to make duplicates of all analog transmitters in digital and not use channels 0-5A. This can mean different antennas are required. Sometimes the polarisation changes as well. There are also a number of high powered sites using vertical polarisation for VHF and horizontal polarisation for UHF.

If you take the Darling Downs as an example all stations are in band 4+ (channel 28-50) with Southern Cross on channel 0. This antenna should be removed when converting to digital. In Toowoomba, all stations are in band 5 so no antenna changes should be required provided the installation is in good condition. The ABA has tried to allocate digital channels in the same band as analog ones so that a minimum number of households have to buy new antennas.

So yes there can be differences between digital and analog antennas particularly at VHF.

Questions on this post should be in this strand.

AlanH

thanks for the insight on helping to receive digital tv more successfully !!!! i was just wondering i have a rover tda 6 digital and analogue field strength meter and it seems to be quite good but not totally sure on the ber readings and what they actually mean. i am aware that its a level of the amount of info received into stb and the errors have to be kept to a minimum . i have been informed that the best measure for ber is <10-8 is this true? and with other readings how do you translate? would appreciate some help thankyou!!!!!

Carlton
Meters generally give two BER measurements,The first is the channel BER which is the BER of the signal as arrives at the input.This is sometimes referred to as B BER on some brands of meter as it is the BER BEFORE viterbi correction.

The second BER measurement is the post viterbi BER or PV BER sometimes referred to as A BER or AFTER VITERBI BER.

People are always looking for the magic pass/fail good /bad type of figures.

STB,s will just show a perfect picture with Channel BER as low as 1e-02 and a PV BER just under 1e-04 but these are absolute minimums.

A Channel BER of 1e-04 or higher would be a realistic value for reliable service.This would generally relate to PV BER of 1e-06 - 1e-08

Did you get your antenna system sorted out? I also am in Perth - i had installed my antenna system myself and have had excellent result. PM if you would like some more information.

thanks for your help bellotv appreciate it !!! is there anywhere where i can get more info on understanding the formulas for ber some of the readings are a bit strange to me like "1x10-4" etc

Ewoud,
I have been away without contact with the forum. I am now reading the 27 pages of new posts!
Have you read WA Geographic Viewers' Forum. WA subforum Select your geographic subforum and then open Get the best reception. Which transmitter and which antenna

Connelly is also subject to salt spray not only on antennas but also on the power lines which can cause the picture to break into blocks and the sound to chirp.

Depending on your location (can you see the Darling Range in the Bickley area) or not. If you can use one of the first recommendations for the Main transmitter, if not I would use the weak signal recommendations.

Any further posts should be in the Perth Viewers' forum.

AlanH

I'm looking at trying one of the TF160 high pass filters. Given it's a "trade" filter it probably won't come with much in the way of instructions. I'm sure I can figure it out but one thing I want to check is should it be installed before or after the masthead amplifier?

I'd prefer to put it after to save getting up on/in the roof until I see if it actually works if that possible.

HP filter needs to be installed before masthead to stop lower frequencies (and hopefully the impulse noise) from even being amplified and more likely in the case of impulse noise from overloading the amp.

Fitting it after the masthead is like shutting the gate after the horse has bolted.

But will it work (at all) after the amp? Just as a temporary test to save me the time of climbing up into the roof just to test. It's only the outlet that has the STB on it that I'm concerned with. If it works, even only as a reduction rather than complete cure I can then look at installing it permanently.

It will work to an extent, however if you have already amplified the offending signals/interference it may be totally useless.

is there an amp avail to cover the entire uhf range as mt tamborine on the gold coast hinterland trans mits from uhf 36 - sbs to uhf 68 nbn digital.

thanx


7seven

apsilon,
You have not said where you are. Click on Geographical Viewers' Forums. Subforums Select your geographic subforum and then open Get the best reception. Which transmitter and which antenna
Post any further posts on this topic in your geographic viewers’ forum.

The some masthead amplifiers come with filters included. Anything which is not wide band .

7seven
Kingray MHU44G B1-3 -1 dB, B4-5 44 dB

AlanH

Carlton,

In order to understand BER, please use the following example:

BER = Bit Error RATIO (NOT RATE!) Rate is Incorrect terminology and means something totally different.
It is the ratio of errors present within the incoming data stream.
And is measured before and after viterbi / error correction.

Then... Usually a BER meter/instrument would normally display the 1x10-4 as a 1E-5
In any case, 1E-4 would mean
1 Error in every 10,000 Bits of Information (data) received.
Notice the (-4), you can make this the NUMBER OF ZEROS you must add to the initial number.

If your instrument is displaying a 10 before the Bit number, then it would equate to 10 + 0000 zeros. Ie: 100,000 but you will need to check on this from your user manual but logically I would bet it to be like this.

The same goes for 5E-3.
This would equate to: 5 errors in every 1,000 Bits received.
or 3E-2 would equate to 3 errors in every 100 bits received.
Of course, the less number of zeros (or you could call it the order of magnitude) the worst your signal is.
A bad signal would be 1E-2 and probably your signal is on the border line of falling off the cliff edge.
A fantastic signal would be 1E-8 (ie: a perfect incoming signal)
However, be aware...if you are getting 1E-8 AFTER viterbi (error correction) and a lower reading like 1E-3, then you would have to look at your antenna setup to try and get a better signal.
You really should aim for the best possible incoming signal measured BEFORE viterbi (error correction).

I hope this is easy enough for you to understand. If you still have trouble, please let me know and I will explain in a different way. But I am pretty sure you will understand now.

AlanH,

Is there a reason why you always refer to Kingray?
They are not the best solution for the above problem!

There are many other Mast Head Amplifiers that will do the job better and WITH RF shielding for a much lower price and higher quality.
The MHU44G is NOT RF SHIELDED. IT IS IN AN ENTIRELY PLASTIC CASE! And very inviting for Impulse noise.

Maybe you can try a Fracarro JS2RT or even the Fracarro MAP series.

It all depends on the incoming signal.
If it is too strong and you use a high gain mast head, you will over drive the amplifier and destroy/clip the signal.

In your case you mentioned an MHU44G which has 44dB gain on UHF right?
However, if the incoming signal is very high like...say...70dBuV and because the MHU44G has a final output of 108dBuV, you will actually overload the amplifier because:

70+44=114dBuV (this is 6dB over the MAXIMUM Input allowed)
So sure, now you can say you will just turn down the input attenuator and sure that is fine.
You will need to attenuate by 6dB to get to the maximum allowed, but will you have minimum noise?
And remember that the MHU44G is an INPUT stage Amplifier, Not Mid stage so there is NO gain control! Just input attenuator so your noise factor is increased.

But what if the person in question has a huge signal like 85dBuV off the antenna straight to the TV outlet?
Many people make the mistake of thinking that because the set top box doesn't work or the analogue picture is bad, it must be because of low signal... Then by adding a masthead you actually make the problem even worse.

7seven, can you supply a CHANNEL POWER & CARRIER TO NOISE READING?
This would help greatly in solving your problem.

Sure you can also say that the signal received by the person in question might be very low, then that is a different story to a certain extent. But remember that the Kingray Masthead that you have recommended is NOT shielded but in a plastic case. For digital, this is NOT recommended!

Then, if you are using the mast head as a filter...well then there is something wrong with your thinking.
Filtering is done by filters, not mast heads unless you want to perform a multitude of operations at once which includes amplification.

Also, AlanH, I am not sure why you are saying that Salt spray will make digital reception pixelate and the sound to chirp. Among the many reasons why this could be happening, most of the time it is because of two things. Either too little or too much channel power or impulse noise but I am betting it would be impulse noise more than anything.

Digital TV is present in MANY countries INCLUDING countries that have a coast line like Australia, Italy or Vietnam for example. In both cases, salt spray is NOT a factor. It is usually Impulse noise or other reception factors.
But salt spray...that would have to be the most silly thing I have ever heard... sorry

Digital Docktor,
The reason I have been recommending Kingray is because of the internal filtering. I am looking a band pass filter of 174-230 MHz for band 3, 526 - 589 for band 4, 526 - 680 for band 4+ and 680 - 820 MHz for band 5.
In particular I do not want gain in the 45-174 MHz band.

This minimises interference and allows the maximum gain to be set. The only source of overload is other analog TV transmissions in that band. If yoiu can find others, then I will certainly recommend them.

As for shielding, the amount of metalwork in antennas particularly band 1 - 3 is considerably more than the input wiring to the first transistor of the masthead amplifier, so I would rather have a filter than shielding if I had to chose. So the antenna is a much better antenna than the wiring in the masthead amplifier.

I agree that overloads are a possibility These amplifiers contain gain controls. I also agree that an antenna which is restricted to the frequency range of interest and has adequate gain is preferable. Getting sufficient signal level from the amplifier through long cables is also important to minimise interference and overcoming cable loss. You will notice I have said this is general advice in the Geographic Viewers' forums. Here I have only recommended them for diffuse and weak signal areas.

The fact that masthead amplifiers can make the situation worse has come up many times on this forum.

Filtering can be anywhere but it must be prior to any amplifer and as close as possible to the input. Otherwise you get intermodulation . This will then "transfer" the interfering signal to the frequency of the channel being amplified. Then no filter can remove the interference. Putting the filter in a separate shielded box then makes is much more expensive because of the extra weather proof case, pcb, dicast box and connectors.

Salt, Australia is an island surrounded by ocean where most of the population live. The Mediterranean is a sea so is smaller.

The problem with salt is that it accelerates the corrosion of the steel screws (which connect to the down lead) and the aluminium they screw into. The oxides in rust are a semiconductor and as a result will cause the intermodulation mentioned above. I have seen analog pictures from a corroded antenna with the windscreen wiper effect. So for digital the inpulse interference will worsen as the corrosion increases.

The other problem with salt is that it gets on high voltage power line insulators. This causes them to arc when there is moisture. Typically at tea time! The arc will produce many frequencies gradually reducing in power as the frequency rises. However the power line is the aerial! Where I live the power company washes the salt from the insulators to prevent blackouts.

One poster lives near a 225 kV power line and can tell you all about it, even the acoustic noise you can hear from the power line.

AlanH

Oh give me a break please!

MHU44G pdf

I must be using a different product, there seems to be a midstage gain control in this model

Marcj,

Yes I have clearly made a mistake in my comment. I did not see this pdf before I made that comment so I will give you that, but it doesn't change the gist of what was said.
It is funny you have pinpointed this particular thing though... No problem...
I will now be extremely alert and include some quotations of particular persons in the future

AlanH,

Sure you have selected the Kingray because of the band pass filtering...However, this doesn't change the fact that if you might have too much signal and you will over drive the amplifier and make the situation worse.

The first thing that should always be done before anything else would be to KNOW the ACTUAL signal received. I have never seen anyone ask a question on what type of Channel Power, CNR or BER this particular person is receiving at the outlet point.
Ie: the Channel Power and CNR of each individual carrier in the particular bands.
ONLY THEN can one make an informed decision of which type of mast head amplifier to use. And no one can argue with that. Without proper measurements, we are all flying blind.

Then...about shielding on mastheads and that you stated "As for shielding, the amount of metalwork in antennas particularly band 1 - 3 is considerably more than the input wiring to the first transistor of the masthead amplifier, so I would rather have a filter than shielding if I had to chose. So the antenna is a much better antenna than the wiring in the masthead amplifier." Sorry mate, that is absolutely rediculous!
Do you not know that many impulse noise problems ingress at the mast head and connection point and many times because of non existent shielding or even impedence missmatching... Even the masthead you recommended, it is a saddle and screw type. Not even F-Connector and also just plastic cover with NO SHIELDING. http://www.gme.net.au/matv/mhu_series.php

Also your comment QUOTE:"[color=#C0C0C0]Filtering can be anywhere but it must be prior to any amplifer and as close as possible to the input. Otherwise you get intermodulation . This will then "transfer" the interfering signal to the frequency of the channel being amplified. Then no filter can remove the interference. Putting the filter in a separate shielded box then makes is much more expensive because of the extra weather proof case, pcb, dicast box and connectors."
[color=#000000]Well actually I agree with you, the filtering must be before the amplifier, but usually always at the headend. Imagine you have ingress at the headend but you insert a filter before a trunk amplifier down the network. That is just wasting time. However sometimes the interference is BEHIND the actual carrier that you are trying to reticulate and therefore not possible to filter with normal filtering. But this is very important because when it comes to Impulse noise or other similar type of interference, the problem occurs BEHIND the actual carrier that you are trying to reticulate and by using equipment that has NO shielding, you are making the probability much higher. And when you are mentioning about metal boxes etc... if you compare the fracarro product pricing to Kingray pricing, and remember that the Fracarro product is Shielded, the fracarro pricing is much lower in cost than Kingray and you get a better product anyway. And no I do not work for Fracarro.

Finally, about the salt issue. I'll have you know that I have lived on an island and other countries on the coast not far from Australia for many years and some of these places have digital and very salty atmosphere with high and low humidity. I can tell you that what you are saying is rediculous and extreme. Yes, the salt causes corrosion etc... but the actual problem here is IMPULSE noise. But sure, you can say that arcing is what is generating the impulse noise and I will give you that, but to say it in this context is quite silly. There could be 10s of different reasons why there is impulse noise present.
In the islands and other countries that I have lived in, and have both sat and terrestrial digital, problems were generally because of impedence missmatching, ingress, poor connections/connectors, poor quality cable, non earthing of headend or antennas, mercury vapour lighting and dirty motors... the list goes on and on. Not once has there been an incident which was caused by overhead high voltage electrical cables arcing when there is moisture unless of some extreme scenario.

Even the poster that lives near a 225kv power line can talk about the Audible acoustic noise that they can hear, doesn't mean that this is the reason for the pixelisation. In the end, BER, Channel Power and CNR (all together) are extremely important. If all parameters are comfortably correct and you have pixelisation problems, then you can start looking at impulse noise etc... but I would be starting with the house lighting, any motor driven equipment even nearby, or even checking the actual TV system if that is the case... Has this person checked every single RF connector? Are all connections F-Type? What type of antenna?, what type of mast head (if any)? what type of cable used?, what type of outlet wall plate used?, what type of fly lead? Is there an impedence missmatch in the system? etc... The electrical power lines would be the last thing that would be looked at. Could even be that the signal received is just hanging off the edge of the cliff. But without actually Measuring the channel power, CNR & BER, no one can say what the cause is, not even myself. Sorry

OK.

I am simple. As I have used this particular item the error was obvious.

There was also a sense of deja-vu, but I can't quite put my finger on it........ think I'll go on another holiday.

Marc.

I know the sense of dejavu now.

New poster appears plugging Fracarro. (along with making sensible observations)

?Is he Poidahl/Peter/Pietro in another guise?

So would the good Herr Doktor Digital care to explain for me what his agenda is here? I wouldn't want to be misguided.

Marc.

Marcj,

No guise here. Just want to give my 2 cents just like everyone else but I am tired of reading stuff that is just not true.

And no I am not any of the above persons you mentioned either.
And I do not know who poidahl is (i can't even pronouce the name), but I know who peter and pietro are and I can assure you I am not any of them in disguise.

However, Yes I have obviously dealt with them on a business level because I purchase my stock from laceys, OBVIOUSLY, but I can assure you I am not one of those persons. I did, however, go to uni with one of those persons but I will not say who
Bloody Typical...of course because I am plugging Fracarro you would be so suspicious to think that I am working for the aforementioned persons and I have an alterior motive...sorry to dampen your hopes

What about AlanH, is he working for GME Kingray maybe? He seems to plug kingray all the time???
Maybe he is taking a bit of payola on the side for plugging kingray on this site for so long!
Why are you not suspicious of him like you are with me? Absolutely Rediculous...

Hi there Dok

I suppose you were once an excellent installer who has managed to climb up the ladder now right?

Everyone here is allowed to give his 2c worth of info...without an attitude and AlanH doesn't have one.

Cheers

PS: I suppose you use Unaohm as well right?

Hi there cofdmstuff

No actually I am still an installer!
And I do not have an attitude either. Maybe I'm a little raw and people can sometimes take that the wrong way because I say what I think but... thats life I guess
Maybe I might have to take diplomacy classes

P.S. Actually I have two instruments. One is a Rhoden Swartz and the other is a Kathrein.
And I have a HP network analyzer too.

Cheers

Digital Docktor,

Firstly, I have no business connection at all with any manufacturer, wholesaler or retailer despite what you may have been told.

On overload I have mentioned this possibility in my Geographic Viewers' Posts where masthead amplifiers are only mentioned in weak signal areas. As for antenna basics this area is already covered. Measuring the signal levels to prevent overload is always a good idea. However there is nothing to stop a strong signal from local arcing from modulating a weak TV signal within the amplifier even to the point of clipping. Hence filtering.

I do not understand this technical term behind. There is nothing stopping you putting another filter in prior to distribution if there is a long cable from the antenna to the distribution point. The point is that filters should be prior to amplification to prevent intermodulation.

I have not been concerned about pricing provided the best result is achieved. That is a customer's choice.

Causes for BER to be poor.
Poor signal to carrier ratio. If the signal level through the antenna system is low and local impulse interference is high the BER will be high. If however the signal level in the antenna system is high then the local impulse noise will be a smaller proportion of the signal and will havel less effect on the BER

Momentary gaps in signal and poor shielding will let the impulse interference in due to poor cabling and connectors. The other factors I agree with.

You do not live in an area where the electricity company has many pole top fires caused by the arcing I mentioned every autumn. At one stage they lost power to a major city for more than a week! Just because you have not experienced it does not mean it does not happen. I would not expect Melbourne to have much of a problem with this because it is not on the ocean.

You should remember that the first radio transmissions were from spark gap transmitters which is what all arcing sources are. They have a wide bandwidth right up into the VHF band. The way they affect the BER is that the arcing signal is going to change the data being received. Error correction can only work so far. The measurement of BER would have to be instantaneous and not average values to pick these effects up.

Impulse interference is so bad this is why the ACMA made the decision not to allocate any digital transmissions below 174 MHz. (channel 6)

I would like to reiterate that I have recommended Fracarro products on my lists and would be happy to recommend any amplifiers which have filtered inputs to the channel combinations we use.

Finally you mentioned in another post that the Fracarro Log Periodic antennas have the CAI seal of approval. This is straight from the Fracarro Website. Unfortunately the CAI is an British organisation. The UK does not use band 3 for free to air TV. The European scene is so croweded with stations that band 4-5 antennas are mostly used. In Australia we have band 3 predominating, and the ACMA has selected band 3 & 4 only for capitial cities, band 4+ for high powered regional areas (where possible) and band 5 for low powered repeaters. We can optimise the antennas required. We also have a huge country where as in Europe congestion is a big thing and long distance is not considered.

We also use mobile communications, UHF CB and pagers in the European channels 21-28 which can also cause poor BER due to interference.

We also use vertical polarisation extensively which changes antenna requirements.

So do not blindly quote other countries' experiences that should apply in Australia.

AlanH

AlanH and DoktorDigital

What's going on here gents. Lots of advice, diagreement and yet where there's agreement you are both wrong

Firstly I smell a rat here somewhere, I cannot conceive of someone have a piece of Rohde and Schwarz equipment and making such an abysmal effort in spelling the name.

One glaring error is that the fact is on amplification is that you don't always have to have the filter before first amplifier. You two have pressed the opposing view so often either you simply have no idea what you are talking about or limit your experience to what you can get from a Dick Smith or Jaycar catalogue.

Wake up you two, if you don't know what you are talking about, keep it to yourselves.
The poor sods whose only reference is this web site just need the facts.

James

Alanh,

Hmmm...



Actually masthead amplifiers are also used in Metro areas where the signal is extremely low such as valley like areas in the CBD (sydney melbourne brisbane). However, it should be mentioned that you should ALWAYS measure the signal at each and every job. If an installer is using a portable tv to check the signal, then they are not a professional installer and should go and do something else because it just gives our specialized profession a bad name.

The technical term BEHIND could be explained by:
Imagine you have a spike or another digital carrier, which could be referenced as interference (ie: 2MHz wide/bandwidth) and at a channel power of 50dBuV with CNR of 30dB referrenced to 235MHz. The actual placement or frequency of this "interference" is at 225MHz on the terrestrial band.
Now combine this "Interference" into a signal that is received from your antenna and lets use channel 12 Digital for this example..
Now tell me how to filter this "interference" with a normal filter???
I bet you can't - and no, you do not know where the interference carrier is coming from but let's just say it is some uni student playing around with some rf gear but you cannot tell him to turn it off.
Also because this is an example, you can not answer this by saying that you will call the ACMA and ask them to terminate this interference. This example is only to help you understand the point I am trying to get across to you.



actually you said in the earlier post...

so I don't understand what you are saying here???

Then...


Actually, what causes poor BER are many things but I think you are trying to say is LOW CARRIER to NOISE, NOT Signal to Carrier (maybe you made a typo here???). But Impulse Noise and Earth/system Noise (related to physics) are two different things here. Maybe you are tired today...
But...the fact of the matter is that the smaller the Carrier To Noise Ratio (that is the smaller the Carrier in Relation to the Noise), the worst BER you will have. Remember that the CARRIER is the messenger of data to the receiver. If there is not enough data (ie: large enough carrier in relation to the noise factor) then the receiver cannot display an image.
Impulse noise is different but will have the same effect as the "Interference" as stated above.



How do you know where I live and where I have lived in the past. In one of my earlier posts I mentioned that I lived on some islands and other countries along the coast. So why do you say that I have not experienced anything ???

And

well, this is a subject that posess great passion for in this country. In actual fact, just by putting 7MHz carriers in the VHF band just made life all the more difficult for everyone.
NEARLY the whole world runs on 8MHz channels (and no i did not say everyone) and where digital is concerned, MOST countries have allocated them in UHF @ 8MHz.
I don't know what it is but we always have to do things the hard way here in Australia...for what reason??? God only knows...

And as far as what other countries do, I have lived in many countries (I am 45 years old) and I can tell you that there are other countries that use Band 3 for FTA TV. If you like I can provide you with links to different sites if you want to be convinced or even better, google search the stuff and you can try and prove me wrong. Good luck... However yes, the CAI have approved the LP45N Log periodic, but that doesn't mean that the LP345 will not perform in a similar manner. I believe you understand what I am saying but maybe you don't like it because I am not talking about hills or something???
Finally, I will have you know that many countries use Vertical Polarization, including Italy, so don't be so quick to quote on other countries if you do not know anything about them.

Doktor Digital

James T Kirk,

Mate, I never said I am perfect and I am the first to admit it...
And sure, I made a typo (Rhode & Schwarz) sure I forgot the "ch" and ??? what is your point here?

Can you give a constructive REASON why you think that if it is an error that you don't ALWAYS have to put the filtering behind the first amplifier?
Give us all an example of your reason and intelligence why this is the case!

Go on, please enlighten all of us... I am eagerly awaiting your interesting and enlightening reply !
(of course you must follow the same context of what was said)

P.S. And there is no rat here. Just a very interesting debate. No hard feelings, just trying to get to the facts...

Cheers

DoktorDigital

Smelling a rat:

I looked at the quality of your written word, very few spelling mistakes and those that are there can be attributed to typo's. Then there's "Rhoden Swartz", spelt it as if you have never seen it written before, it just doesn't gel.

It is a point of particular frustration when I am challenged to explain something that if you had any real grasp of the subject you would know when to back off. However for the purposes of assisting those others reading here the reason is as follows.

The advice to place a filter before the amplifier is general and good advice that will give significant improvement in the huge majority of cases. It is also the safest option for installers with little experience.

There are however situations where the amplifier should be used first.
Classically these are situations where there is very marginal wanted signal levels and yet C/N (carrier to noise ratio) is reasonable and at the same time some local significant signals are present. In this situation if the filter is placed before the amplifier, the filter's insertion loss eats into the already marginal signal.
By originally placing a very linear low gain (10-20dB) amplifier stage prior to the filter and careful positioning of the receive antenna, these losses are overcome and the resulting signal will present the receiver with a better C/N ratio without the intermods the uninitiated might expect. This is no theory, it's in use and delivers superior results in this application.

James

Docktor Digital,
I have not disagreed with you about measuring signal levels, and have recommended it in posts.

As for behind see the post on about Penrith. The interfering signal can easily be removed by a filter provided it is before any non linear circuit. Ie an amplifier. Afterwards its too late.

As for separate filters, it is much easier to add the small coils and surface mount capacitors with the amplifier on the same circuit board, than house them separately and it will perform better.

You are right about carrier to noise ratio. As far as this is concerned we are saying the same thing. If the carrier to noise ratio is low the BER will be high, however if the C/N ratio is large and the BER is high it is likely to be delayed signals & interference and reflections in the cabling.

As far as RF band width is concerned all transmissions in the Americas are 6 MHz wide, in Europe VHF is 7 MHz wide and at UHF it is 8 MHz. This then requires all receivers to have 2 SAW IF filters for dual bandwidth.

Here we have the same number of channels available as in Europe but we have 56 MHz for mobile communications.

If you look at the Geographic Viewers' Forums you will find viewers receiving signals over large distances 80 km is not uncommon.

The salt story is true.

AlanH

James, you are just trying to wind me up. What alterior motive could I possibly have behind a spelling mistake? You are taking this totally out of context and you sound like one of those ignorant so and so's who say that they've been in the industry for 40 years, and they know everything...

Yet when I ask you a very simple question to give an explanation on why the filter before the amplifier is not important, you answer it with such a rediculous example. You obviously have no idea of how RF works and you should go back to school and learn before you open your mouth or write about such silly things.

You say that you analysed all my previous posts and how the majority of the spelling is correct, yet you have failed to understand what was written and the context of the discussion.
If you had read properly, you would have understood what we were talking about and that is completely different to what you have mentioned here. And still, you have no idea what you are talking about. But I like a challenge, so I will back my comments up with fact! Not like you do

Here is why...
If you have two carriers (but each carrier is a DIFFERENT service ie: Channel A & Channel B ) on the same frequency, there is no way you can take out the un-wanted channel with the type of filtering you described.
The only way you can eliminate the unwanted channel is by positioning the antenna so that it receives the least amount of the unwanted carrier. As to what you are saying, its absolutely crap! There is no way you can filter out that channel (IF ON THE SAME FREQUENCY AS DESCRIBED ABOVE) by inserting a filter after an amplifier stage of any gain. By Amplifying the particular Channel (ie: the full 7-8MHz bandwidth where BOTH carriers are present) all you are doing is just that...AMPLIFYING BOTH CARRIERS !

Still don't believe me...ok, just set up two analogue modulators (reason for analogue is because Digital modulators are out of most people's budget) and set BOTH modulators for channel 50 (681.25MHz).
Now connect the RF output of One of the modulators to a 2 way splitter (in reverse) and connect the output (which was the input) of the 2 way splitter to your spectrum analyser and view the actual TV picture (which the modulator is obviously connected via A/V to a video source different to the second modulator).
Now without taking your eyes of the picture, connect the RF output of the SECOND modulator to the Second port of the 2 way splitter (in reverse) and turn the modulator on and see what happens to the picture now.
This is with analogue! and you can imagine what happens to the data in digital. (This of course is just an example but I believe gets the message across).
Now try and use that silly filtering example that you made before to fix the picture...I bet you cannot!
Now who looks silly?

Also, CNR, In Digital scenario, is not the most important factor. You can have a fantastic CNR and channel power but if you have an interference behind the wanted carrier, your BER will suffer.
Also CNR measurements are referenced to another frequency which has NO carrier, but just noise present.
And if you have carrier A that has a CNR of 40dB and carrier B (which is behind carrier A so to speak) which has a CNR of 25dB (if you could measure it that is - or turn off the transmitter that is transmitting carrier A), then your true CNR would be 15dB by rights.
And although BER and CNR are mathematically related, doesn't mean that if you have a good CNR you will necessarily have a good BER.

You just don't know what you are talking about and suggest you go back to school to learn RF and English and stop trying to baffle people with bulldust. Your example makes absolutely no sense whatsoever!
So if you want to continue to make a fool of yourself, keep tit for tatting... But I CHALLENGE YOU TO PROVE WHAT YOU SAY IS CORRECT! Good luck Otherwise give it a rest!

AlanH...this could go on forever...

Just a quick one before I stop posting on this subject...

I agree with you about filtering MUST be BEFORE the amplifier so we are saying the same thing but in a different way. It's just good ol james.t.kirk that can't get his brain around the concept. Not sure he ever will

Same goes for Carrier to noise, we are saying the same thing.
And yes, in the USA is 6MHz just like Japan, all the way through all bands (of course NTSC). And Europe is 7MHz VHF and the Superband (PAL). But 8MHz in the Hyper/external Superband and UHF so no gripe with you there either.
And yes I agree that viewers are receiving channels from 80km away is also possible. I never said it wasn't. Even further with the right antenna and optimal atmospheric conditions...the ionosphere can do marvelous things with RF in the right conditions!

But, although your salt spray example could be real, it is not the reason why everyone that is near high voltage powerlines experience pixelation.

Anyway...

DoktorDigital

Not even close my friend. Try another forum to wind people up. Knowing you cannot filter out in band interference with a filter is pretty basic. Try reading what was written and with experience over time you may learn how to describe it technically.

James

James,

hehehehehehehehe...Very poor comeback...try telling us how to ACTUALLY filter it out rather than a meaningless reply like that...
It just shows that you are full of BS and nothing constructive to say!

Go on, I challenge you to tell all of us how to filter the second carrier WITHOUT removing the number 2 input and putting a filter AFTER the splitter or imaginary amplifier...Try to PROVE me wrong instead of just saying I don't know...I want to know how to do it because you are such a knowledgeable person...
GO ON we are all waiting

DoktorDigital

I didn't come down in the last shower sonny, stop trolling and wearing out your keyboard with very long explanations of what the technically savvy can pass on in a few lines.

By the way, who were you last week before you decided to try DoktorDigital?

On the other hand, if you are genuinely unable to grasp what I have already described fully in very simple terms, then I apologise because there is little I can do for you!

James

Doktor digital
I,m only a mere TV technician /antenna installer and not an RF engineer like yourself or James but I interprete from what James is trying to say is that as a typical filter has an insertion loose of around 1-2dB,If you put it after the amp you would get a better carrier to noise at the outputthan if you put it before the amp.
I also interprete that he is suggesting that this is only suitable where unwanted singals will not be so high as to overload the amplifier and he recommends using amplifiers that a very linear so that intermodulation is minimized.
He is not saying that it will remove the "behind signal".Infact he mentions careful positioning of antenna to address this issue.

There is logic in this method especially if you are in a very terminally weak area to squeeze out the last drop from the antenna.

Otherwise you have said some intersting things.

I liked and finally understood your last description of the "behind signal" ,Der finally get your point.

This sounds like the argument of why MER is more important than CNR because it is a measure of the channel and the behind the channel interferrer.

James...get a life...you have got no idea what you are talking about and now everything is getting out of hand. There is no need to offend me by calling me a troll.

But you are yourself so ignorant of RF that you have not understood one word that was written in my posts.
They are long because if I don't bloody cover every single possible angle, there will always be a smartass like you to pick on a hole that I have left out. This is typical of people that know nothing and profess that they know everything...Like YOU James!

And if you continue to reply on this thread, you will see that you are only showing everyone how silly you are for the simple FACT OF THE MATTER THAT YOU CANNOT EVER ANSWER ANY OF MY QUESTIONS OR CHALLENGES WITH ANY REAL TECHNICAL FACTS... ALL YOU DO IS INSULT!

You either give some constructive arguments so we can debate this like civilized persons or just shut the hell up! Simple like that!