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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?
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In this section
Official aerial installers guide to the TV spectrum future1
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Digital Region Overlap4
Freeview reception has changed?5
Two frequency interference 6

Friday, 18 August 2023
Andrew Steele
2:54 PM

We get our TV signals from the Stockland Hill transmitter in Devon. We have to use an aerial in the loft due to restrictive covenants on the properties. Until April or thereabouts we had great reception. The transmitters were retuned when the BBC added HD to local news.

At that point, after the retune, we have found that the signal strength was poorer across the board but particularly so on the COM4/SDN multiplex.

A masthead amplified which included 4G/5G filters fixed everything except for SDN.

For BBC1 on channel 101 we get Signal Strength 96-98% Quality 98-100%

For 5USA on the SDN multiplex we have Signal Strength 90-92% Quality 0-45%

The Arq multiplexes are fine.

I'm not sure where to report the issue. Any suggestions or, indeed, thoughts on options to fix...?

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Andrew Steele's 2 posts GB flag
Steve Donaldson

5:30 PM

Andrew Steele: Retuning following the change to regional BBC One HD wouldn't make any difference to the signal, providing when the retune was carried out it tuned to the signals from Stockland Hill, and not those of another transmitter.

You may have already confirmed this, but just in case, the channels from Stockland Hill are PSB1=C26, PSB2=C23, PSB3=C29, COM4=C25, COM5=C22 and COM6=C28.

Without know where you are it isn't possible to specific, so it is only possible to be general. This is why a postcode is requested.

A tree or trees could cause degradation of reception, this quite possibly affecting one or more but not all channels (multiplexes). This could be a tree close by, in the immediate vicinity or on ground, typically a hill, somewhere between you and the transmitter. April and May is when the leaves grow on the trees which could impede reception. It sounds like this was the time when you noticed degradation in your reception. You say that the mast-head amplifier resolved some of the issues. If you need an amplifier when you didn't before, it sounds like something has changed in the path between the transmitter and your aerial.

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Steve Donaldson's 211 posts GB flag

6:57 PM

Andrew Steele:

If this issue has suddenly got worse this week, Stockland Hill transmitter is currently listed for Planned Engineering with, quote, "Pixelation or flickering on some or all channels".
This could be the cause of current issues and it looks like it's going to be listed again next week!
If it's been more of a continuous issue, apart from checking out everything in Steve Donaldson's excellent post, make sure all your coax connections/plugs are good, clean and free from corrosion, also check there's nothing like scaffolding very near or solar panels etc fitted that may be having an effect.

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Chris.SE's 4,187 posts GB flag
Saturday, 19 August 2023
Andrew Steele
3:45 PM

Chris.SE: Many thanks. The issue has been for a couple of months following a retune required by the addition of local news to BBC HD channels.

Had a different aerial chap in yesterday and found a slightly better position for the loft aerial and seems to have resolved things for now. Thanks.

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Andrew Steele's 2 posts GB flag
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