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Single frequency interference

What to do when several channels are missing, but they are all on the same 'multiplex'

What to do when several channels are missing, but they are all
published on UK Free TV

There are several different type of interference that cause problems. This page deals with the situation where:

There are two main causes of this type of intermitted interference: The current Freeview mulitplexes are shown in this diagram. If all of your missing channels are on a single row, you have "single frequency interference":



Local analogue interference

Local analogue interference is caused by household video devices that you can attach to a television such as:
  • Sky Digibox;
  • Video cassette recorder (VCR);
  • Personal digital video recorder (PVR);
  • Games console;
If you have any of these devices, you will need to work out which of these is blocking the reception of a Freeview multiplex by turning off the suspect device and then rescanning for channels on the Freeview box.

If powering off the device restores the Freeview channels from the blocked multiplex, you will need to either stop using the problem device's RF output by disconnecting the RF output cable permanently, or by changing the RF channel number that that device uses. See, for example, How do I change the RF output channel on a Sky Digibox?

You can find a list of the frequencies that are not in use at your location by putting your postcode into the My Freeview reception and looking under the "Free RF channels" section.

Non-wideband aerial in some areas

In some places you will need a wideband aerial to receive all the Freeview multiplexes. For example in Central Birmingham, the Sutton Coldfield has multiplex D on an 'out of group', so you cannot view Film4 or ITV2+1 without an aerial upgrade.

To find out if you need an aerial upgrade, see My Freeview reception.

Help with Freeview, aerials?
How do I get a test card with Freeview1
I would like to know if it is possible to receive UK terrestrial Freeview servic2
I have been told I would receive too much singal from my Freeview tansmitter as 3
Can my Freeview box receive more than one BBC and ITV region?4
Is it true that my 87 year old mother is entitled to a FREE upgrade when the ana5
In this section
Official aerial installers guide to the TV spectrum future1
Which free digital TV system will give me the most reliable reception?2
High pressure causing channel loss through "Inversion"3
Digital Region Overlap4
Freeview reception has changed?5
Two frequency interference 6

Comments
Saturday, 5 July 2014
J
jb38
sentiment_very_satisfiedPlatinum

1:38 PM

RC: As the other TV's in your system are unaffected, then you should test the aerial outlet point used by your recorder / Sony TV using one of those, if though the TV's used on your other system are of different brands to each other then its best to try both to allow for variations in tuner sensitivities.

It would also assist if your location was known, this being to access info on the transmitter covering your area.

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jb38's 7,179 posts GB flag
R
RC
2:59 PM

Thanks JB, I'm in Crawley (rh11) - is that Crystal Palace? Will have a look at swapping tv's round tomorrow - not looking forward to the aggro though....

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RC's 3 posts GB flag
J
jb38
sentiment_very_satisfiedPlatinum

4:14 PM

RC: Indications are that Crystal Palace is the most likely transmitter dependant on where you are located within the RH11 postal code area, as in some places Reigate might provide a better signal.

However if your aerial is mounted horizontally then it will be Crystal Palace as signals from the Reigate TX are vertically polarised, the latters ArqB Mux being on C27 whereas C28 from Crystal Palace.



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jb38's 7,179 posts GB flag
R
RC
7:15 PM

How bizarre ... when I switched the box on again this afternoon, I got that 'new channels found' message and suspected it might be the ARQB set. Hit 'ok' and next thing I know I'm watching Tour de France coverage on ITV4 for two hours without any problems whatsoever. Still OK now, and those extra channels have magically reappeared on the TV too - ie when the box is switched off.
Will see how long this lasts, but one thing's for sure, I won't be responding to any more 'new channels' messages - so frustrating when it actually loses them rather than finds them...
Anyway, it's a horizontal aerial, so it's C28 - will be handy to know that for future manual tuning purposes if the reception starts going wonky again. Thanks for your help JB!

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RC's 3 posts GB flag
J
jb38
sentiment_very_satisfiedPlatinum

7:54 PM

RC: Many thanks for your update, pleased to see that the problem has seemingly been rectified, although another couple of days will soon reveal if your problem was simply down to a glitch having occurred in your box, or maybe not as the case may be! because if indeed it was the box then the channels should not have vanished on your Sony TV if ITV4 was being received via the TV's tuner.

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jb38's 7,179 posts GB flag
Thursday, 31 July 2014
J
Jeremy Flint
12:23 PM
Mansfield

A strange problem - we have Humax HDD recorder (PVR9300) which intermittently fails to record audio content. The original box has been replaced and still the problem exists. The problem has be there for over a year now. The box is manually retuned and everything can be ok for anything upto a couple of weeks then the problem reoccurs. It can happen on any channel and at any time of day. My aerial, which is brand new, is on Waltham transmitter with a masthead amplier fitted. I have asked and am informed that no 4G masts are near me.Yesterday the audio dissapeared while I was actually watching the channels through my box as well (not when recording) The picture is fine with no pixelation or break up. Any ideas?
My postcode is NG20 8LP......

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Jeremy Flint's 1 post GB flag
Jeremy's: mapJ's Freeview map terrainJ's terrain plot wavesJ's frequency data J's Freeview Detailed Coverage
Friday, 1 August 2014
J
jb38
sentiment_very_satisfiedPlatinum

12:36 AM

Jeremy Flint: Out of interest, what strength / quality indicates do you see if you leave the box sitting on either the BBC or ITV and carry out a signal condition check? this achieved by pressing "menu" and selecting then pressing on the bottom icon on the left.

View the indications for about a couple of minutes for the purpose of observing if any fluctuations are seen in either the strength or quality indications.

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jb38's 7,179 posts GB flag
Monday, 25 August 2014
B
Barrie Perkins
11:41 AM

I live in NN4 Northampton, having erected a wide band aerial on a pole on my bungalow , yesterday I tuned in four televisions of which one told me I had about 70plus channels all with a quality of 10. Today Monday I have no signal on all televisions. If I put my aerial meter a on any television the lights are the same as yesterday. I have now connected a television on the end of the aerial lead, before the distribution amplifier and have the same message NO SIGNAL. If I put my meter at the same point it is showing the same as yesterday with a good signal..I am now running out of ideas. Can anyone advise where I go from here.

link to this comment
Barrie Perkins's 1 post GB flag
J
jb38
sentiment_very_satisfiedPlatinum

3:28 PM

Barrie Perkins: If, as I suspect, the aerial meter being referred to is of the type that provides dB level indications by means of LED's, then those types are only useful for signal "strength" reference purposes and not, as far as DTT reception is concerned, the most important indication of "quality", plus of course they cannot differentiate between the frequencies etc of signals being picked up, but just the fact that RF signals are being picked up.

If you receive Freeview from the Sandy transmitter and not the more local Dallington Park, then if any of your TV's indicate strength and also quality (not combined) go into the tuning menu / manual tune and enter but "do not scan" Ch24 (BBC), as on most equipment if anything is being received, no matter how low, the strength and quality of will be indicated on the level bars.

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jb38's 7,179 posts GB flag
Monday, 1 September 2014
B
Barrie Perkins
4:30 PM
Northampton

Hi jb38
Ch24 as per your instructions shows a signal strength of 50-70% but no signal quality.
I have approx the same readings for Ch21, and slightly lower on 27 and 32. No channels have any signal quality at all. Why occasionally when I turn the televisions on do they work OK. The aerial to the mast amplifier, and the mast amplifier to the distribution amp in the attic have been rewired with quality satellite cable, and I have connected a television in the attic before the distribution amplifier. Confused!!!

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Barrie Perkins's 1 post GB flag
Barrie's: mapB's Freeview map terrainB's terrain plot wavesB's frequency data B's Freeview Detailed Coverage
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