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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.

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In this section
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Friday, 6 April 2012
3:26 PM

We live near Orpington and tune in the Crystal Palace. When we first bought an Integrated DigiTV we had a new aerial installed and had all the Digi programmes. Then we started to have problems with some channels missing. OFCOM couldn't find a problem when I called them in.
Anyway, we then got all the channels back with no changes to the equipment until recently when MUX2 (Freq Ch22) totally disappeared. Signla strength Zero. But we still had the channels listed.
Of course, on 04 April, I had to resan both my TV and PVR, so MUX2 listings (ITV, CH4, CH5 etc) are no longer listed.
I can't see why we get perfect reception on all other MUXs but zeroz on MUX2.

Any ideas ?

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AndyH's 7 posts GB flag
Dave Lindsay

4:06 PM

AndyH: It's pretty likely that the situation will resolve itself on 18th April. Until then, keep manually tuning to C22.

Longer explanation:

Digital receivers have a signal threshold above which they will show a picture and below which they won't. For analogue receivers, the quality of signal is proportional to the signal strength and there is no threshold.

So let's suppose that when you previously received ITV, C4, C5 etc that the signal level coming down your aerial lead was "only just" above that which your tuner needs to resolve a picture. Now it is "only just" below that which it needs. The difference between the two may be quantified as being "tiny".

Perhaps with the other channels you were a "tiny" bit *above* "only just" having enough signal level and thus a "tiny" drop would leave you still with "only just" enough above the threshold and thus to use your description, "perfect" reception.

Signal levels vary a bit all the time due to changes in atmospherics.

Before switchover, digital signal levels are lower which means that whilst some will have good reception, others (on the outside of the transmission area) won't have any at all and those inbetween will sometimes have it and sometimes not.

For the ITV, C4 mux, with the aerial as you have it, you are evidently borderline now. The situation will change on 18th April.

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Dave Lindsay's 5,724 posts GB flag
Lesley Southern
6:47 PM

Lesley postcode L33 Kirkby I have lost all ITV multiplex 2, only happened today, any ideas? Thanks

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Lesley Southern's 1 post GB flag
8:53 PM


Thanks for your comment. I do realoise that a digital signal just above the threshold will give a perfect picture and one just belopw no picture at all, however,the signal level on C23 is 75-80% and on most of the other MUX (eg CH34) it's around 65%. MUX2 (CH22) is ZERO.

I've tried the attenuator suggestion made elsewhere on this group (in case C23 is desensitising the front-end of the set) and then had picture break-up on some of the lower power MUXs, but still no CH22.

All I can hope is that CH22 will, indeed, come good after 18/04 ! - unless anyone else has any suggestions ?

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AndyH's 7 posts GB flag
AndyH's: mapA's Freeview map terrainA's terrain plot wavesA's frequency data A's Freeview Detailed Coverage
Dave Lindsay

9:32 PM

AndyH: It is surprising that you get nothing on C22.

The Tradeview predictor for your post code says 92% served for C22 whereas the other standard definition pre-switcher multiplexes are 99%. There must be a reason that it has calculated it like this. There appears to be no other transmitter on C22 that could be interfering at your location.

I can only think that perhaps CP throws out in your direction less signal on C22 than on the other pre-switchover channels. Thus the contrast between the low C22 and C23 may be greater than another side of the transmitter that throws out more signal on C22.

Based on the predictor, try tuning to C41 for the equivalent multiplex from Sudbury and Rouncefall (which broadcast this together on the same channel as a single frequency network). This might give you some degree of service until 18th April.

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Dave Lindsay's 5,724 posts GB flag
Monday, 9 April 2012
9:54 AM

I have an LG32LT-75 with built in recorder,since the retune on 4 april recorder does not work and the tv locks up after about 5 minutes and you cannot change channel,in an on the Reigate Transmitter

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Pete's 1 post GB flag

5:09 PM

Pete: This is a known issue with this model and which was supposedly rectified with an over-air download, but though you should be aware that this model is extremely sensitive to the signal level received, and which should ideally be between 70-80% as the problem experienced can be triggered even if just under 70%, and at the top end with variations of the problem being witnessed if over, so have a look at the strength being received.

You might already know this, but the signal strength screen is accessed by pressing: Menu / Set up / Diagnostics.

That said, I would suggest that you wait until after the 18th before doing anything, as work is taking place all the time, but should you find that the signal levels presently seen on BBC are within the figure stated then you should have a word with LG support regarding the software issue, as unfortunately I don't really have knowledge of what the latest figure should be.

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jb38's 7,179 posts GB flag
Wednesday, 11 April 2012
Anthony Nash
1:07 AM


Only the otherday I changed from a separate TV and freeview box to a combined Sharp LC24DV510K TV/DVD/Freeview. From the looks of it I am missing all of rows 2 and C. My previous setup had no problems picking these up. My post code is CV34 4DX. I have re-tuned several times and removed devices such as games console. I can't tell you much about the aeriel, as this is rented property, however, there wasn't a problem yesterday with the old system.

Thanks in advance.

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Anthony Nash's 1 post GB flag
Anthony's: mapA's Freeview map terrainA's terrain plot wavesA's frequency data A's Freeview Detailed Coverage
Sunday, 15 April 2012
8:04 AM

I have a sony Bravia KDL26P2530. The number of channels that I can get on Freeview varies all the time. Sometimes I have 57, sometimes 40 and sadly I always loose the better one and NEVER the buying/selling channels!! I have re-tuned several times. Nothing has changed in the installation.. 3 years ago I got a count of over 80 channels.. today no chance. I have no games consoles, nothing not even a DVD player linked to it. Just the TV..

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Emma's 2 posts GB flag

9:36 AM

Emma: Could you give more information about the area in which you are having reception problems, preferably with a postcode?- so a check can be made of predicted reception after which more specific advice can be given.

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KMJ,Derby's 1,811 posts GB flag
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