18 replies to this topic

[alanh]

For more detail read Antenna Design Basics + Amplification

This list is selected on the basis of the channels covered only and quotes the appropriate website’s antenna gain.

The higher the number of dB the larger the antenna, the more sensitive and more directional it is. It is also more expensive. The advantage of getting gain from the antenna rather than an amplifier, is that the antenna becomes more focussed thus rejecting delayed signals and interference sources. Amplifiers can become overloaded which antennas cannot. Thus amplifiers can make reception worse.

If the antenna signal is too strong at the receiver, a low cost attenuator can be used. The advantage of this method is that any interference picked up by the cabling is also reduced.

Yagi – Band 3 Channels 6-12 and Band 4+ Channels 27-49
Horizontally polarised local reception and medium distance)
Vertically polarised diffuse reception (either long distance or blocked by terrain)

Matchmaster catalog, section 1
Nil

Hills Antennas
SMX14B4+ Band 3 6-8 dB Band 4+ 8-13 dB?
SMX24B4+ Band 3 7-9 dB Band 4+ 8-16 dB?

Laceys TV - Fracarro
Nil


WISI
Nil


Nationwide Antenna Systems
ANTSQUE2S/S Channels 6-12, 28-46 Band 3 7.5 dB Band 4+ 10.5 dB
ANTSGL2 Channels 6-12, 33-50 Gain ?
ANTSGA1-4/5 Channels 6-12, 28-46 Gain ?

Phased Array - Band 3 Channels 6-12 and Band 4+ Channels 27-49
Vertically polarised local reception and medium distance)
Horizontally polarised diffuse reception (either long distance or blocked by terrain)
Nil

Clipsal
2ANCOMD14 Gain Band 3 7.5 dB Band 4+ 12 dB
2ANCOMD24 Gain  Band 3 15 dB Band 4+ 8 dB?

AlanH
Please post any errors and omissions here

Edited by alanh, 19 March 2009 - 11:12 PM.

[Jeffry]

alanh, on May 15 2006, 12:00 AM, said:

For more detail read Antenna Design Basics + Amplification

This list is selected on the basis of the channels covered only and quotes the appropriate website’s antenna gain.

The higher the number of dB the larger the antenna, the more sensitive and more directional it is. It is also more expensive. The advantage of getting gain from the antenna rather than an amplifier, is that the antenna becomes more focussed thus rejecting delayed signals and interference sources. Amplifiers can become overloaded which antennas cannot. Thus amplifiers can make reception worse.

If the antenna signal is too strong at the receiver, a low cost attenuator can be used. The advantage of this method is that any interference picked up by the cabling is also reduced.

Yagi – Band 3 Channels 6-12 and Band 4+ Channels 28-49
Horizontally polarised local reception and medium distance)
Vertically polarised diffuse reception (either long distance or blocked by terrain)

Matchmaster catalog
Nil

http://www.hillsante...nnalo.pdf]Hills Antennas[/url]
SMX14B4+ Band 3 6-8 dB Band 4+ 8-13 dB?
SMX24B4+ Band 3 7-9 dB Band 4+ 8-16 dB?

Laceys TV - Fracarro
Nil
WISI
Nil
Nationwide Antenna Systems
ANTSQUE2S/S Channels 6-12, 28-46 Band 3 7.5 dB Band 4+ 10.5 dB
ANTSGL2 Channels 6-12, 33-50 Gain ?
ANTSGA1-4/5 Channels 6-12, 28-46 Gain ?

Phased Array - Band 3 Channels 6-12 and Band 4+ Channels 28-49
Vertically polarised local reception and medium distance)
Horizontally polarised diffuse reception (either long distance or blocked by terrain)
Nil
AlanH
Please post any errors and omissions here

Matchmaster B3, B4+, cross polarised is 01MM-D14-HVB. Very similar to Hills UV13 and virtually identical performance. Not shown in latest catalogue but still available; older catalogues show it as B4 UHF but it has been recut for Ch28-50.

Phaselink PL10-6/12 is very compact B3, B4, B5 (any polarity combination) that is very compact and often outperforms the Hills and Matchmaster items. Two of my suppliers have just advised me these are being discontinued -Don't know why as they are a very popular aerial (check any caravan park).

In fringe areas, like here (Gulgong), combo units just don't hack it. Any of the normal yagi B3 antennas (from many manufacturers) are fine but signal test recommended to determine which is required. Why Buy a 14 element when 6 elements will suffice?
Fracarro also do single channel yagis for any B3 channel in 6 or 11 element. Could be ideal for Ch12 from Mt Cenn.
For UHF any of the common 18 element B4+ aerials are good all-round performers but the one I have found outperforms any other is Hills SF91B4+. Not cheap but, hey, what did you expect?
For digital only the Fracarro narrow band yagis are best value for money. !0 element gives 11 to 12 dBd gain and 20 element gives 12 to 14 dBd (genuine too -I have tested them). But.....(always a downside) they only cover a restricted frequency range -not enough for combined analogue and digital but perfect for a digital only installation. Very reasonably priced too. 4046 version (Aus Ch34-49) ideal for Canobolas etc.

cheers
Jeff

[alanh]

Jeffry,
There is a link for all combinations of bands and polarisations.
There is a link to caravan and mobile antennas (typically marine) into which I would have put the Phase Link antenna. It would not be in this section because it is not supposed to receive band 5.

A single channel antenna will always give the best and strongest signal for its size. So the Fracarro single channel antennas you mention would be in the Band 3 only link.

What I dislike about the specifications from manufacturers' is that they quote the maximum gain but no minimum gain or a graph would be better. Of course the gain is relative to a dipole at that frequency so the testing becomes more laborous, because the "transmitting" antenna has to have its length changed for each channel tested.

Check this out Comparative DTV signal outputs from antennas

AlanH

[bellotv]

Alan
Your link to Hills isn't working for me

[alanh]

BelloTV,
It worked for me, however it should not have displayed the whole address, so I have edited it to look like all the others.

Do you have any comments about Comparative DTV signal outputs from antennas whose link is in the previous post.

The reason for the non band channels was to see what channel ranges are required for all bands to have a similar output from a dipole.

To get the high Q to restrict channel 69 to 7 MHz would require a large surface area to minimise the resistance due to skin effect.

AlanH

[bellotv]

That worked.
No comments as I only use B4+ or B5 on transmitters arount here for digital.
Unfortunately we still have B1 for ABC analog so band 3/4 only is not used

[Neil_Moe]

G'day Alan & others,

alanh, on Mar 10 2007, 08:23 PM, said:

A single channel antenna will always give the best and strongest signal for its size.
Check this out Comparative DTV signal outputs from antennas

Based on the above information (sepecially the graph in the pdf)  it seems to show that multiple channel antennas suffer a 20 to 25dB signal loss when compare the single channel antenna for same channel.

It would appear that for ppl who are out on the deep fringe, (ignoring costs) they should get a single channel antenna for each channel they want and then diplex them to create a single feed. ????

The only variable would be the insertion loss of the diplexing arrangement, assuming your could diplex 4 VHF antennae & one or two UHF together.

Is such an installation possible?

Ta,
    Neil.

[alanh]

Neil,
You can get single channel band 3 antennas, but not UHF. So all you can do is to use the ones with the smallest number of channels in their band. With UHF phased arrays, they only make them for the whole UHF band.

Read Antenna Design Basics + Amplification, Terms and comparison of types will give you the advantages of phased arrays.

Diplexers are really a set of filters so for their pass channels they have much less losses than splitter/combiners.

AlanH

[wahroonga farm]

alanh, on Mar 10 2007, 08:23 PM, said:

Check this out Comparative DTV signal outputs from antennas
AlanH

alanh, on Mar 10 2007, 08:21 PM, said:

All,
Attached is a graph of the signal output vs channel number. Its calculation includes the fact that as the channel number increases, the width of the antenna decreases, decreasing the signal output.

If the range of channels to which the antenna is designed is reduced to a single channel the signal strength remains the same. However if an antenna is designed to receive all digital channels from channel 6 - 69 the sensitivity to any individual channel drastically drops.

This is the reason I have made different antenna type recommendations for every viewing area in Australia.

The best reception occurs when the antenna used is one designed for only the channels to be received. In weak cases separate antennas for different bands give a better result such as band 3 and band 4.

http://www.dtvforum....t...ost&id=2807

AlanH

Alan, I don't understand the "DTV Comparative Signal Strengths" graph. Can u explain a bit more and the maths behind it?

Tks

[bellotv]

Neil_Moe, on Mar 17 2007, 01:54 PM, said:

G'day Alan & others,
Based on the above information (sepecially the graph in the pdf)  it seems to show that multiple channel antennas suffer a 20 to 25dB signal loss when compare the single channel antenna for same channel.

It would appear that for ppl who are out on the deep fringe, (ignoring costs) they should get a single channel antenna for each channel they want and then diplex them to create a single feed. ????

The only variable would be the insertion loss of the diplexing arrangement, assuming your could diplex 4 VHF antennae & one or two UHF together.

Is such an installation possible?

Ta,
    Neil.

Nei
As far as I'm aware there is no diplexor available that can combine VHF channels.EG 6,8,11,12.
Your theory is good to use single channel antennas however they are NOT single channel ONLY antennas and therefore do pick up the other channels as well but obviously not as well.

If you combine them in a VHF combiner (say a splitter in reverse) ,you may find that the residual channels picked up by other antennas combine in an unpredictable way giving an end result which is better/worse on various channels than using a single wideband antenna.

The only way that I can see that single channel antennas on the VHF band (where several channels are used) can be efficiently used is to connect each single channel antenna to a single channel amplifier EG the Fraccarro K120 series .Fraccaro also have masthead single channel amps which are cheaper but still you need 4x $170 from memory + 4x Single channel antennas + UHF antenna =UHF mast head .

K120's  ultimate but cost prohibitve to general household installation

[alanh]

Wahroonga Farm & BelloTV,
I have posted this reply with the graph for the use of others. Comparative Signal Strength Graph

AlanH

[wahroonga farm]

Hi alanh,

I'm still unable to find the correlation between your graphs (showing an alarming 20-40dB loss for a wideband antenna vs a single channel antenna) and typical manufacturers antenna gain charts.

Isn't widebanding what Yagi-Uda's are so good at?

What are the actual design specifications of the single channel and wideband antennas used in the plots?

[alanh]

Wahroonga Farm,
The antennas you are looking at are designed for mulitple channels. The graphs are relative to a dipole at the frequency of measurement. So as the channel number increases the output from a dipole will drop. This is not shown in manufacturers' graphs.

Yagi-uda antennas are essentially narrow bandwidth, you have to detune them to widen the channel range.

The plots of direction are for the channel specified on the the graph. Single channel antennas have a bandwidth of one channel of 7 MHz.

AlanH

[wahroonga farm]

alanh, on Mar 18 2007, 02:29 PM, said:

..... So as the channel number increases the output from a dipole will drop ..... AlanH

Yep I get this part cause it's due to physics ... but not the rest. Oh well

[bellotv]

wahroonga farm, on Mar 18 2007, 09:28 PM, said:

Yep I get this part cause it's due to physics ... but not the rest. Oh well

The rest is also due to physics
A yagi Designed for One particular frequency will be resonant at that frequency have a high Q.
High Q resonant curcuit Has a very narrow bandwidth.IE it has maximum gain at its center frequency and drops rapidly either side of this.

Great  say if you want to use it on 146.75Mhz only.

Since our TV channels are so wide 7Mhz each and several per band ,a single frequency optimized yagi wont do ,so we have to lower its Q to widen its bandwidth but as per Physics ,If we lower the Q,we also lower the gain at resonance but it gives us a flatter bandwidth which is what we want for TV .
Unfortunately we have to lower the Q by detuning the yagi from perfection by altering the length and spacing of elements away from resonance


If we design an antenna for say about 400Mhz
A 20 el yagi has a gain of say 20dB at  2Mhz bandwidth
A 20 el yagi has a gain of say 15dB at 20mHz bandwidth
A 20 el yagi has a gain of say 10dB at  200Mhz bandwidth

Which is what AlanH's  Graphs are trying to show
Your 20 el yagi will give the most bang for your buck if you purchase it to cover only the channels you need.

[alanh]

BelloTV,
I agree

Q = resonant frequency/bandwidth = Reactance/Resistance

AlanH

[wahroonga farm]

Yeah but yeah but yeah but.

The graph very specifically shows 20-40db loss for all sorts of 'odds 'n sods'.

What are the design parameters for the thing(s) the graph is plotting. It has to be quantified.

[alanh]

Wahroonga Farm,
A single dipole to the centre of the channel range stated, for all graphs. The thickness of the dipole will determine its Q, hence the amount of magnification at that frequency. I have converted the change in voltage to dB which is more realistic. I have also included the increase in radiated power used by the TV stations.

AlanH

[bellotv]

Alanh

After rechecking graphs and re reading all I to am confussed Like wahronga farm.

Is each antenna the same in each band group .IE are they all 10 element yagis pehaps ?

If so,is this what you are referring to about the dipole being center tuned to ?

Or is this graph about using a diople  like rabbit ears and adjusting length to center of required band?This I dont think so as I would have expected curved ( bell more like) shaped graphs instead of the straight lines
In fact I would have expected all the graphs to be this way however maybe you did the straight lines for simplicity and this have caused me confussion

Does this graph include log periodics ? If so how does this correspond to cener tuning as they consist of multiple tuned elements.