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Intermitent Signal Breakup


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#1 PhillT

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Posted 06 November 2011 - 01:58 AM

My problem is that I'm not sure where my problem really is. :huh:

Every few minutes, never less than 5 minutes apart, and rarely more than 7 minutes apart, the picture and sound breaks up for anything from a split second, to 4 seconds.

I have watched the inbuilt Signal Meter, and it shows that the signal strength (around 75) stays constant during these breakups, but the signal quality goes from a steady 96/99, to zero, then for a couple of seconds can be anything up to 40, then goes back to a steady 96/99 until the next "scheduled" breakup about 6 minutes later.

I am at a loss as to where the problem is, but it can only be the TV (Dick Smith) itself, the aerial (a good quality powered indoor dish type, also Dick Smith), or there is a problem with the actual signal being received.
The TV and the aerial are only a few months old, and all was fine until the last few weeks.
The fact that the signal strength does not waver during these events suggests that the aerial is OK, doesn't it?

I'm not sure exactly what can affect "Signal Quality" to that degree, and on such a regular schedule.

Any help would be greatly appreciated, so I can approach Dick Smiths with a reasonable argument if it is a component issue, and not a signal issue.

Thanks.
Phill

#2 mtv

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Posted 06 November 2011 - 09:02 AM

My problem is that I'm not sure where my problem really is. :huh:

Every few minutes, never less than 5 minutes apart, and rarely more than 7 minutes apart, the picture and sound breaks up for anything from a split second, to 4 seconds.

I have watched the inbuilt Signal Meter, and it shows that the signal strength (around 75) stays constant during these breakups, but the signal quality goes from a steady 96/99, to zero, then for a couple of seconds can be anything up to 40, then goes back to a steady 96/99 until the next "scheduled" breakup about 6 minutes later.

I am at a loss as to where the problem is, but it can only be the TV (Dick Smith) itself, the aerial (a good quality powered indoor dish type, also Dick Smith), or there is a problem with the actual signal being received.
The TV and the aerial are only a few months old, and all was fine until the last few weeks.
The fact that the signal strength does not waver during these events suggests that the aerial is OK, doesn't it?

I'm not sure exactly what can affect "Signal Quality" to that degree, and on such a regular schedule.

Any help would be greatly appreciated, so I can approach Dick Smiths with a reasonable argument if it is a component issue, and not a signal issue.

Thanks.
Phill



Phill,

Where are you located?

Where are you receiving signals from (which transmission site)?

Model of TV antenna?

From your description, it sounds like some form of electrical impulse noise interference.

#3 alanh

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Posted 06 November 2011 - 10:20 AM

Phill,
Go to the Geographic Forum where you live.
Read the "Get the best reception" the first post for your area.
Follow the instructions there, including the link to indoor antennas.

Post any further posts on this topic in that Geographic Forum as the answers are specific to your location.

AlanH

#4 PhillT

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Posted 06 November 2011 - 12:28 PM

Phill,

Where are you located?

Where are you receiving signals from (which transmission site)?

Model of TV antenna?

From your description, it sounds like some form of electrical impulse noise interference.


MTV, I am at Dardanup West.

The antenna is from Dick Smith Indoor TV Antenna with Built-in Amplifier
Model:
Cat#: DSAU_L4069
$59.99
Basically it is a mesh dish with a flattened oval loop which can be rotated for horizontal or vertical polarization, plus two telescopic rabbits ears.

Transmission is from Furguson Valley, only about 15 km away from me.

#5 mtv

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Posted 06 November 2011 - 01:21 PM

MTV, I am at Dardanup West.

The antenna is from Dick Smith Indoor TV Antenna with Built-in Amplifier
Model:
Cat#: DSAU_L4069
$59.99
Basically it is a mesh dish with a flattened oval loop which can be rotated for horizontal or vertical polarization, plus two telescopic rabbits ears.

Transmission is from Furguson Valley, only about 15 km away from me.


Phill,

Given your close proximity to the high-powered transmitters, it's possible your tuner is being overloaded by the amplifier built into the antenna.

Ideally, you need a wideband UHF antenna on your roof, pointed at the Mt Lennard transmitters.

The amplifier will also be amplifying any impulse noise interference.

Electric fences are commonly the culprit with impulse noise, as is industrial machinery and equipment.

Apart from installing the correct roof-mounted antenna, you could try an indoor antenna without an amplifier.

Just turning off power to your existing indoor antenna is not the same as removing the amp from the circuit altogether.

#6 steveb

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Posted 06 November 2011 - 05:12 PM

Can I suggest that if it is regular breakup, it sounds like an impulse noise problem (especially considering the use of an indoor antenna).

Check to see if the breakup coincides with the start up of a refrigerator motor. Maybe you have an old beer fridge somewhere, or an older fridge in the kitchen?

See if the breakup and the motor cycles line up.

#7 PhillT

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Posted 06 November 2011 - 07:05 PM

Phill,

Col,…..
Given your close proximity to the high-powered transmitters, it's possible your tuner is being overloaded by the amplifier built into the antenna.


Correct me if I'm wrong, but if that were true, wouldn't I get a signal strength far higher than 75, (with amplification) which is only three quarters full strength ?



Ideally, you need a wideband UHF antenna on your roof, pointed at the Mt Lennard transmitters.


Agreed, it would be ideal, but unfortunately not an option until renovations are complete on the room with the antenna feed.



The amplifier will also be amplifying any impulse noise interference.


This antenna does have an adjustment for amplification, which is set to about a third of the available range. This is the point where I get max signal strength at the lowest gain setting,….any higher makes no difference to strength, or quality.
The antenna is also extremely directional,…even 20 degrees off centre will result in a sharp drop off of signal, so I assume that this would limit it's ability to receive interference from any other direction to some degree?
All the electric fences that I have seen pulse every few seconds, not every 6 minutes, so can we rule them out?
Industry is about 1.5km away, and at about 90 degrees to the antenna direction, so is that likely or unlikely to be relevant?


Can I suggest that if it is regular breakup, it sounds like an impulse noise problem (especially considering the use of an indoor antenna).

Check to see if the breakup coincides with the start up of a refrigerator motor. Maybe you have an old beer fridge somewhere, or an older fridge in the kitchen?

See if the breakup and the motor cycles line up.


SteveB,…
Our fridges & freezers are not very new, and we run a pressure pump for water supply, so I will shut them all down and see what happens.

Thanks for the suggestions gents, at least I have some direction and things to try.

Cheers.
PhillT

#8 mtv

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Posted 06 November 2011 - 08:24 PM

Signal measurements from tuners are notoriously inaccurate.

What does 75% on your 'meter' equate to the industry standard of dBuV?..... exactly, there's no benchmark for comparison.

You could have ten tuners of the same make and model and chances are you would get ten different readings, so, no, a higher signal level on a domestic tuner may not necessarily increase or decrease.

This seems to be proven by your observation.. "This antenna does have an adjustment for amplification, which is set to about a third of the available range. This is the point where I get max signal strength at the lowest gain setting,….any higher makes no difference to strength, or quality.

Given the signals perform better at lower gain suggests there is too much signal.

There may also be a lot of reflected signals from surfaces in the room where the antenna is.

Could you not place an external antenna temporarily whilst renovating?

If the impulse noise is from an appliance in your house, an indoor antenna with an amp will pick up that interference more easily compared to an outdoor antenna.

#9 DrP

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Posted 07 November 2011 - 05:29 AM

SteveB,…
Our fridges & freezers are not very new, and we run a pressure pump for water supply, so I will shut them all down and see what happens.

Electric water heaters can also do it.

#10 DX Fan

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Posted 07 November 2011 - 09:37 AM

I would also suggest getting a long cable for the antenna and moving it to another location in the room (or house), preferably close to a window that faces the TV stations as high as possible.

#11 MLXXX

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Posted 07 November 2011 - 07:24 PM

Every few minutes, never less than 5 minutes apart, and rarely more than 7 minutes apart, the picture and sound breaks up for anything from a split second, to 4 seconds.
...
The TV and the aerial are only a few months old, and all was fine until the last few weeks.

Post any further posts on this topic in that Geographic Forum as the answers are specific to your location.

MTV, I am at Dardanup West.
...
Transmission is from Furguson Valley, only about 15 km away from me.

Alanh,
wouldn't it more appropriate to classify this query as likely to relate to the subject of local RFI as could arise anywhere in Australia; rather than being likely to be a topic unique to a particular geographical region in Australia?

PhillT,
another device to consider as a potential source of RFI is a pc. However what a pc would do every 5 to 7 minutes is not clear. Also a pc normally needs to be quite close to an antenna to be a problem. I agree with the suggestion of a refrigerator as a plausible candidate. It could start up every 5 to 7 minutes and cause a reception glitch.

#12 alanh

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Posted 07 November 2011 - 07:33 PM

The reason it is location specific is that the channels used for transmission require a band 4+ antenna not a wide band UHF antenna for the best rejection of interference. SBS34, SSW (GWN) 35, ABSW36, SDW (TENWest)37, vacant 38 WOW (WIN) 39 or Digital restack group C.

Secondly the area has SSW3 and ABSW5 analog which are in the FM band There are high powered FM transmitters on this transmission site. In other areas of Australia these channels are not used, so FM filters can be switched on in masthead amplfiers to remove FM interference. If you do this in the Bunbury area, you loose a pair of TV signals, leaving only SBS33, WIN40 analog.

Bunbury is now the only location in the world, using a high powered channel 5, 101 - 108 MHz TV transmitter (300 kWerp)

The assumption of impulse interference may not be correct, it may be FM interference?

This means that existing analog antenna installations often give problems which is peculiar to this area, particularly the use of RF channel 5.

AlanH

Edited by alanh, 07 November 2011 - 07:48 PM.


#13 MLXXX

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Posted 07 November 2011 - 07:52 PM

The reason it is location specific is that the channels used for transmission require a band 4+ antenna not a wide band UHF antenna for the best rejection of interference.
Secondly the area has SSW3 and ABSW5 analog which are in the FM band There are high powered FM transmitters on this transmission site. In other areas of Australia these channels are not used, so FM filters can be switched on in masthead amplfiers to remove FM interference. If you do this in the Bunbury area, you loose a pair of TV signals, leaving only SBS, WIN analog.

Those considerations are valid if the source of the offending RFI cannot be located and reduced; and if does not actually occupy the bandwidth of the desired signal and lie in the direction of the desired transmissions. I think that at this point in time, energy is being devoted to tracing the source of this particularly regular glitch in reception.

#14 alanh

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Posted 07 November 2011 - 08:22 PM

MLXXX,
You need to learn about intermodulation distortion.
The glitches you talk about are are generally generated at frequencies under 1 MHz, so should never affect TV transmissions. This is not true, because of intermodulation distortion.

Intermodulation is problem in any amplifier including audio amplfiers.

So there is justification for making specific geographic forum to recommend the most appropriate antenna, so that it can be used as a filter to minimise the pick up of non wanted transmissions. This will depend of the channels used and the polarisation.

AlanH

Edited by alanh, 07 November 2011 - 08:31 PM.


#15 DrP

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Posted 07 November 2011 - 09:04 PM

The OP's opening post gives sufficient information to rule out inteferrence from other permanent transmissions in the area. If certain people would spend a tad more time actually understanding the content of posts instead of wandering off on tangents this forum may well become useful again.

The TV and the aerial are only a few months old, and all was fine until the last few weeks.



#16 MLXXX

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Posted 07 November 2011 - 09:07 PM

MLXXX,
You need to learn about intermodulation distortion.

Why assume that amplifier non-linearity (THD/IMD) has produced high order harmonics or intermodulation products when the commutator of an electric motor can produce an extended range of RFI directly?

As you would know, a spark gap generates radiation over a broad range of frequencies. A short-lived broad spectrum RFI can be produced by the arc created when a mains device is switched on or off. Even a thermostatically controlled fish tank heater, domestic iron, or coffee maker can result in brief arcing, though inductive loads such as electric motors tend to be more problematic. These forms of interference are worse at VHF, and only weak at UHF frequencies. This webpage shows RFI produced by a treadmill motor at up to 150MHz: http://randombio.com/interference.html

I have an old domestic electric fruit juicer that produces a very wide range of RFI products when the on switch is depressed, enough to unsettle a DAB+ radio at close range, and to cause broad spectrum RFI right across the FM broadcast band, not just if the FM radio is nearby. It creates visible interference to analogue UHF TV reception (Channel 28) even though the TV is 10 metres away and is connected by coaxial cable to an external antenna. I presume something is fauity as regards RFI suppression. The juicer would be about 30 years old.

What we are looking for as the the most likely explanation of the reception fault is a source of RFI with a periodicity of 5 to 7 minutes, and which lasts for a short time, but long enough to unsettle a DTV receiver. It is of course possible that RF overload is being triggered by high intensity RFI at frequencies much lower than the DTV frequencies involved. I note that one of your favourite suggestions alanh for RFI is FM radio interference, not the FM radio transmission that accompanies the video of an analogue TV broadcast, but FM stations in the 88-108 MHz FM band. In fact you have raised this possibility at post #12 above, but what we are dealing with here is reported interference at regular intervals of 5 to 7 minutes. It seems unlikely FM radio transmissions would create interference with such precise regularity and so briefly.

Another way PhillT could monitor the situation would be with a portable AM or FM radio tuned to a vacant frequency. If the DTV reception glitch occurred simultaneous (or nearly simultaneous, allowing for DTV decoding delay) with a burst of AM or FM broadcast band interference, the radio could then be moved closer to suspected sources of RFI. This could help if it is a neighbour's device that is causing the problem (a device that cannot be heard to start up when listening for it in PhillT's residence).

Edited by MLXXX, 08 November 2011 - 03:30 AM.


#17 M'bozo

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Posted 08 November 2011 - 04:46 AM

Any help would be greatly appreciated


Since analogue transmissions are still available from this site, I would be watching them to see what artefacts (if any) are there, or occur in the same time frames.

#18 alanh

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Posted 08 November 2011 - 07:36 PM

MLXXX,
The only way you can prove whether intermodulation is occuring is to use a spectrum analyser which will give you the actual frequencies. I am aware that a wide range of frequencies are produced, however the strongest are at the lowest frequencies and the strength reduces as the frequency increases.

In your link levels of -70 dB is very weak.

All but one of the graphs in your link show what I have stated above. The treadmill has a chopped DC power supply. It operates continuously producing interference. This is not the intermittent nature which is the subject of this post.

#19 MLXXX

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Posted 08 November 2011 - 10:46 PM

...
The treadmill has a chopped DC power supply. It operates continuously producing interference. This is not the intermittent nature which is the subject of this post.

It is indeed very curious what would cause a momentary glitch in DVB-t reception every 5 to 7 minutes. If a computer network fired up briefly every 5 to 7 minutes that could do it.

Perhaps PhillT will discover what has been going on, and enlighten us.

#20 clipper

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Posted 09 November 2011 - 07:43 AM

I would also suggest getting a long cable for the antenna and moving it to another location in the room (or house), preferably close to a window that faces the TV stations as high as possible.


As well as the appliance check, this will be the next 'easy' option. The cable extension needs to be good quality- RG6 quad, you can get one made up for you at an electronics shop. Unfortunately, your indoor antenna is not band specific and is also amplifying everything including RFI ( noise).

#21 PhillT

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Posted 16 November 2011 - 03:20 PM

Firstly, thanks to all who took the time to share ideas on this problem.

It has finally been solved. It turns out that my wife was running an incubator in a spare room, (which I knew nothing about).

The incubator switches on at about 6 minute intervals, depending on ambient temp etc,.....anyway, the incubator has (had) a rouge CF globe in it which was causing the problem.
Changed the globe for a fresh one, and the problem is no longer. :-)

Cheers everyone.

#22 M'bozo

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Posted 16 November 2011 - 03:49 PM

a rouge CF globe in it which was causing the problem.


I hope it was a rogue lamp, and not a red one. :D

Thanks for letting us know the outcome.

Been there, done that, sort of. (But didn't think of it in your case).

Long story short had a problem with a dodgy CFL on a 3 way switch in a house which was causing intermittent AM radio interference every 5 seconds or so when it was switched off.

When the lamp was on, there was no interference.

Changed the lamp, and the interference went.

#23 PhillT

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Posted 16 November 2011 - 07:36 PM

I hope it was a rogue lamp, and not a red one. :D

Thanks for letting us know the outcome.

Been there, done that, sort of. (But didn't think of it in your case).

Long story short had a problem with a dodgy CFL on a 3 way switch in a house which was causing intermittent AM radio interference every 5 seconds or so when it was switched off.

When the lamp was on, there was no interference.

Changed the lamp, and the interference went.


Yep, rouge not red ;)

I guess if my case was not the only one, then they have to be added tot the list of suspect appliances.
We have a house full of C.F.s and none of the others is a problem, but the problematic one was a real cheapie. You get what you pay for maybe?

M'bozo, hope to be moving to your part of the world early next year. :D

#24 mtv

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Posted 17 November 2011 - 08:50 AM

Yep, rouge not red ;)


rouge is red.... commonly referring to a cosmetic used to color the cheeks and emphasize the cheekbones. :wub: <<< too much rouge :P

rogue... an undesirable variation from a standard.

#25 MLXXX

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Posted 17 November 2011 - 11:47 PM

Firstly, thanks to all who took the time to share ideas on this problem.

It has finally been solved. It turns out that my wife was running an incubator in a spare room, (which I knew nothing about).

The incubator switches on at about 6 minute intervals, depending on ambient temp etc,.....anyway, the incubator has (had) a rouge CF globe in it which was causing the problem.
Changed the globe for a fresh one, and the problem is no longer. :-)

Cheers everyone.

It did sound like nearby interference fron your own place or a neighbour's. Good to know you've tracked it down.