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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

Saturday, 24 October 2015

2:35 PM

Bill: I suspect your problem isn't with interference, but something much more basic - the state of of your aerial system. Becuase you put your postcode into the site, we can see how far you are from your transmitter. Although the terrain plot does bring up an obstruction about a km from you, DigitalUK reckons you should have a great signal from Pontop Pike, which is less than 30km from you. Indeed, if anything, you'd expect too strong a signal to be your problem.

However, your getting between 44% and 49% - just enough to allow you to pick up the ITV mux, but the BBC is just too low a lot of the time. That makes sense if therer is aproblem with your aerial, at least somewhere along the line. Start with the lead from the wall to the TV. They can have breaks, etc, and getting another one is pretty cheap. Swap out, and see if that helps. Obviously make sure your tuned into the proper transmitter (your kit might have picked up Bilsdale or Fenham first), and the logically follow the signal path back. Could be a cracked connection, which is letting in water.

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MikeB's 2,579 posts GB flag
MikeB's: mapM's Freeview map terrainM's terrain plot wavesM's frequency data M's Freeview Detailed Coverage
Monday, 2 November 2015
Kevin Holley
4:42 PM

Today my Aunt's redistribution in-house stopped working because of significant interference on Channel 23 487MHz. The internal redistribution was using Channel 24 but the (analogue) signal was all but obliterated. Unplugging the roof antenna removed the interference. Has something happened at Sudbury today or could this be due to 800MHz 4G implementation by EE? I moved it to C66 and that seems to be working for now.

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Kevin Holley's 2 posts GB flag
Kevin's: mapK's Freeview map terrainK's terrain plot wavesK's frequency data K's Freeview Detailed Coverage
Tuesday, 3 November 2015
Doug Z
2:05 AM

So tonight (Mon 2nd Nov), again we lost all channels on com6/ArqB from about 20:30 on both the TV and Humax Freeview PVR. All other channels are showing 100% quality - 85% signal strength.
From looking at these pages, outside of transmission problems, I'm assuming 'single frequency interference' is the cause.
I have checked all connections, and checked the possible problem points suggested.
Local Analogue Interferance;
We don't have a 'Sky Digibox'.
The only 'loop through' is via a Humax Freeview PVR to a digital LG TV, they are also connected via an hdmi cable for normal viewing. The 'loop through' is only used to view the TV when the PVR is recording two programs and we want to watch one that is blocked by recording.
We have a VCR/DVD player connected via a scart lead.
We have a Humax Freesat box connected to the TV via an hdmi cable.
We do not have a games console.

Non-wideband aerial;
We have a 32 bay high gain wide band aerial installed externally above the chimney, aimed as best as is possible at the Selkirk transmitter, there are no line of sight obstructions, there is a signal amplifier in the down lead at the PVR, all cables are copper core/copper shield/copper foil screen and all joints are connected with F connectors. Due to the hills either side of us we are unable to receive signals from Pontop Pike or Chatton without raising the aerial another 7M. Our postcode is TD12 4XN.

Reading what channels we should/shouldn't be able to receive, I note Selkirk is not an 'extended HD' transmitter, we cannot receive the channels mentioned except we do receive Motors TV?
Grateful for any help given.

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Doug Z's 1 post GB flag
Doug's: mapD's Freeview map terrainD's terrain plot wavesD's frequency data D's Freeview Detailed Coverage
Friday, 1 January 2016
8:29 PM


Could anyone help. We have had problems with are Freeview reception. We have one aerial which feeds 2 tvs upstairs, these have no problem. But recently another aerial which feeds into a recorder box then into a tv has had problems with interference on certain channels mostly on the ARQA multiplex, also BBC on the odd rare occasions So a while(6months) ago we replaced the cables and it was fine, but now it seems as the winds blow strong(which recently it has I'm sure you know) it causes pixilation and sound stuttering.

We bought a new aerial and installed it today which has fixed the problem, after finding the right position. The signal quality seems to be around 75-100 on all channels but the strength is about 50-70 on all channels. Its not 100 but there seems no problems.

The problem is now all the channels on the AQRB multiplex have very poor or no signal. The recorder box and tv pick them up but its very bad and unwatchable. What could be causing this.

Any help. Thanks Carl

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Carl's 2 posts GB flag
Carl's: mapC's Freeview map terrainC's terrain plot wavesC's frequency data C's Freeview Detailed Coverage

9:17 PM

Carl: The question has to be, have you mounted your new aerial on horizontal polarity in order to be able to pick up the COM7/8 multiplexes? as ArqA/ArqB on horizontal is only radiated at 50Kw, whereas its 200Kw on vertical.

As far as the ArqB signal is concerned, multiplexes are not necessarily always received at the same levels as each other, sometimes corrected by slight raising or lowering of the aerial if mounted on a vertical pole. However, a poor or no signal is inclined to suggest other problems such as can be caused by HDMI leads (if used) running to close to the aerial input coax.

By the way, although signal strength indications are never the same when measured on different brands of equipment , the ideal strength should be around 80% or so, quality aimed as being as near to 100% as possible.

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jb38's 7,179 posts GB flag
Saturday, 2 January 2016
11:23 AM

jb38: Ok thanks jb38, moving the aerial up the pole has improved this a lot. Quality on all channels it near perfect, strength is down for your recommended 80, they vary between 55-75. But much better than before. Thanks for your help.

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Carl's 2 posts GB flag
Tuesday, 9 February 2016
8:02 PM

Hi. Until a few weeks ago we had good reception from Tay Bridge relay transmitter using a (non-amplified) indoor aerial. We are 3 miles away from the transmitter, which we can see as we are on a high level on Dundee Law. We now get intermittent daily interference on the BBC 1 etc group (C41 - 634.2 MHz.) Fitting a filter supplied by a800 seemed to help a bit but doesn't stop major picture and sound break up on these channels at certain times of day - e.g. 11.00 a.m., 4.30 p.m for 1-2 hours at a time. I'm trying to identify another filter which may do a better job. a800 people are very circumspect so it's difficult to either confirm or eliminate 4G as the source of this. Any advice on this would be much appreciated.

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Robert's 2 posts GB flag

11:06 PM

Robert: You might still get too strong a signal - check it and see. 75% is sort of perfect, but it might be just too high, even with an indoor aerial. A cheap attentuator could do the trick, less than a fiver at Toolstation/Screwfix.

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MikeB's 2,579 posts GB flag
Wednesday, 10 February 2016
4:11 PM

MikeB: Thanks Mike. Signal is around 49% - 50% so probably not too strong. I should perhaps add that we have other TVs elsewhere in the house with indoor aerials and so far these have been unaffected. Have also since heard reports of others in Dundee with BBC1 and BBC2 HD affected by G4 so it's looking very much that this is the cause of the problem.

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Robert's 2 posts GB flag
Thursday, 3 March 2016
3:53 PM

Problems with HD. Signal normally about 60% from Caldbeck Mast and can suddenly drop to zero. Programmes recorded are about 70% incomplete ie a hour recording might give me a 10 minute jumpy recording. Have done freeview reset and seems to improve for a while but soon starts degrading again. Have tidied up and checked cables etc to no avail.

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phil's 2 posts GB flag
phil's: mapP's Freeview map terrainP's terrain plot wavesP's frequency data P's Freeview Detailed Coverage
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