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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
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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

Thursday, 3 February 2011
11:28 AM

Thanks once again to you both :) i've taken photo's of my aerial & some others in my area. All aerials are pointing either NW or SE. Mine is SE (Waltham) To clarify something i said earlier - one of the teletext pages said i was using the waltham transmission (or a relay of waltham). Link to photos here: ImageShack Album - 2 images image with a single aerial on is mine. The other image is a mash of the ones on local houses incase it helps. I have marked which transmittor they point to - N for Nottingham, W for Waltham. I've read up on the link you provided about the different aerials. Reading the 'groups' chart leaves me a little confused. Does this mean that unless i get a 'wideband' aerial, i'll never get all the groups? The ladder isn't here yet, but once it is i'll look at getting mine realigned then see how it is then. (NG83HL)

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DG's 3 posts GB flag

2:11 PM

DG: Yes, just to confirm, both Waltham and Nottingham will require a wideband aerial to get the all of the Freeview multiplex, both before and after switchover.

"Wideband" means the aerial will receive signals on all TV frequencies, rather than just a restricted group.

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Briantist's 38,915 posts GB flag

2:30 PM

DG: Well it would certainly appear as though Nottingham is the favourite choice for reception where you are located, I also noticed that all the aerials around you are seen to be mounted on normal poles and not extensions with this rather suggesting that there aren't any particular problems with reception from the Nottingham multiplexes, as indeed as Briantists check has revealed, so if you simply alter your aerial to being vertically mounted I feel that you may well not require to do anything else other than that.

As far as picking up all of the multiplex channels is concerned, its never really a case of not picking something up but more one of how efficient its done, and in your particular case "if" your aerial was originally installed for analogue TV from Waltham then it wont quite cover all the channels you will be requiring as the aerial will likely have been a C/D type, albeit of course it will "still" work with Nottingham but not quite so efficiently as it requires a wideband aerial for satisfactory reception as is stated by Brian in the last posting.

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jb38's 81 posts GB flag
4:33 PM

Hi Briantist, I tried channels 65,55,36 and still no improvement in signal. What else can i do?

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rob's 6 posts GB flag
rob's: mapR's Freeview map terrainR's terrain plot wavesR's frequency data R's Freeview Detailed Coverage
4:39 PM

I'm new to this forum and there's a lot of useful discussion here.

A problem that's cropped up here a lot, I've been trying to diagnose for my daughter for some time. Namely picture and sound break-up, at peak times, on all 4 TVs. The analogue picture is fine.

A new aerial (pointing to the Waltham Tx, her post code is LE9) and 4-way booster(Wolsey Amp WFAV 425-in the loft & Power Supply 100/1 in bedroom) servicing 4 TVs with Freeview Boxes was fitted about 5 years ago and has worked fine until about September last year and gradually getting worse.

After various checks, I suspect either the aerial or the amplifier/splitter. So this evening I'm going to bypass the amp with an F-connector adaptor to the main TV in the lounge and see what happens.

I've asked Dawn if her neighbours have had similar problems and 2 to the left have said not.

I've heard that the Wolsey set-up is not the preferred one for some and I understand why. If the amp does prove faulty then I will wire a 13Amp socket in the loft and get her a new amp. Could anyone recommend a good one?

Any comments or suggestions would greatfully received.

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Tony's 3 posts GB flag

5:15 PM

DG: Under no circumstances should you put an aerial for Freeview reception in the loft. It must have a clear line-of-sight to the transmitter.

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Briantist's 38,915 posts GB flag

5:30 PM

Tony: Just a little point regarding your daughter enquiring at her neighbours, did she ensure that they are viewing on the same mode as her, that being on freeview? and not either analogue or even satellite.

Reception from Waltham has been problematic for many (inc myself) for some time now and although a booster can fail its just not a common thing to happen, especially a Wolsley which is a quality make.

Regards to testing it, a good reliable test for any booster is whilst viewing a TV on analogue mode switch the mains supply to the booster off, if the picture quickly fades to being highly speckled but immediately picks up again on booster re-powering then its almost 99.9% guaranteed its OK.

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jb38's 81 posts GB flag

7:07 PM

rob: Ignoring the bit about the multiplexes, can you see the suggestion on the Single frequency interference | - independent free digital TV advice page?

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Briantist's 38,915 posts GB flag

9:17 PM

Tony: On taking a further look at what you have reported another question I have regarding the problem is, as you mention the break up generally occurs at peak times and affects all four TV's, would it be correct in assuming that they will not all be operating on the same channel and that the problem affects all?

Another line I was thinking along is the possibility of some domestic equipment being used in an adjoining property which is causing severe mains interference, this either being of an airborne carried nature or running along the power lines and entering the booster amp via its mains input, the usual types of domestic appliances guilty of this sort of thing being food mixers or vacuum cleaners with worn motor brushes.

If your analogue signal is good then this type of interference might only be seen as faint white broken lines across the picture, but however capable of devastating freeview "if" the signal level received was not very far above the reception threshold on your equipment, which in your case could possibly apply at times for some reason out with your control.

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jb38's 81 posts GB flag
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