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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?
Can I attach a Freeview digibox to a Combi TV/Video unit?1
My high gain aerial can't get all the Freeview channels I expected2
I can't get Freeview yet, when will it start in my area?3
Are there plans to extend the range of regional variations on Freeview?4
How can I Receive Freeview on two TVs using one box?5
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
Thursday, 28 December 2017
MikeP
7:42 PM

Allan:

To offer any useful advice we need to know exactly where you are in relation to the transmitter so please provide a full post code.

It may be local interference or it may be a few poor connections in your aerial system and the TV set.



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MikeP's 2,039 posts Platinum Platinum GB
Thursday, 8 March 2018
L
Lesley
7:40 PM

In the evenings I get interference from planes, motorbikes and the Docklands Light Railway and these vary at times. This hasn't always been the case but started about three months ago. My postcode is E14 0EF (Poplar transmitter) Apartment block with communal aerial

link to this
Lesley's 2 posts GB
Lesley's: Freeview map terrain plot frequency data R&TI Service digitaluk trade DAB coverage
Friday, 9 March 2018
MikeP
12:33 PM

Lesley:

Are you sure you are getting your signals from the Poplar Freeview Light transmitter? The information at Coverage Checker - Detailed View (the digitaluk trade link below your posting) shows you should get excellent reception from Crystal Palace and have the benefit of a Full Freeview service rather than the 'light' service from Poplar transmitter.

Check which channels your TV has tuned to, your User Manual will tell you how to find that as it's usually on the manual tuning page - but *do not* retune as yet. Crystal Palace currently uses channels 22, 23, 25, 26, 28, 30, 33 and 35. Changes are expected on 21st March 2018, mainly affecting COMs 7 & 8 which move from channel 33 and 35 up to channel 55 and 56. Poplar transmitter currently uses 39, 42 and 45 and these will not change yet.

Check which direction your aerial is pointing. For Crystal Palace it should be aimed at 204 degrees (a little west of south) and for Poplar it should be at 1 degree (roughly north).

Crystal Palace will need use of a wide band aerial, either a log-periodic or a Group T one (it used to need a Group A aerial which will not be any use for COMs 7 & 8 reception) and be mounted with the small bars horizontal. Poplar needs a Group B aerial with the small bars mounted vertical.



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MikeP's 2,039 posts Platinum Platinum GB
Monday, 30 April 2018
B
Bruce Wells
9:47 PM Brighton

Since about January this year stations drop in and out. I can have reception and watching a prpgram and then it switches in and out of being tuned. I retune a number of times. I am in BN2 1QA. We have the tallest building in the street. We have had the areal checked. I am in BN2 1QA. Oh and can no longer get BBC1. BBC4 can get occasionally.

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Bruce Wells's 1 post GB
Bruce's: Freeview map terrain plot frequency data R&TI Service digitaluk trade DAB coverage
Tuesday, 1 May 2018
MikeP
12:39 PM

Bruce Wells:

The symptoms you describe are those of an aerial system that has poor connections. I suggest you check all the aerial connections as far towards the aerial as you can safely reach. It is likely that there is either a problem with the cable itself or some poor connections along the way.

Since you have retuned, you need to check that the TV has tuned to the correct channels. Look at Coverage Checker - Detailed View and use the channels shown there for Whitehawk Hill. Also check that your aerial is a wideband type so it can receive all the available channels (your original group C/D type will give poor reception of several channels). Also check that it is aimed correctly at the Whitehawk Hill transmitter, which is at a bearing of 70 degrees from your location and only 1 km away. As you are so close, check what the reported signal strengths are, you do not want 100% but between 60% and 85% is ideal. If the signal is too strong that can also cause the symptoms you describe. Search for 'Too much of a good thing' on this website for ideas on how to deal with strong signals.



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MikeP's 2,039 posts Platinum Platinum GB
Friday, 8 June 2018
S
steved
11:48 PM

Since the DSO on 6 June we have lost all BBC channels on one of our two TVs. The Samsung is fine, with good signal strength and quality on all channels, but the Sony Bravia won't even find any BBC channels - it was fine before the DSO.

We have a rooftop aerial aimed at Tacolneston transmitter; have done several re-tunes and even a factory reset, all to no avail. There is no other equipment connected or nearby, and no other cables to cause interference.

Have tried a manual re-tune, but no luck. As the other TV is fine is it a problem with the Bravia? Seems odd if the problem only arose after 6 June.

Any ideas?

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steved's 1 post GB
Saturday, 9 June 2018
MikeP
4:06 PM

SteveD:

Please put your full post code into the Digital UK Coverage Checker website at http://www.digitaluk.co.uk/coveragechecker/main/index/dummy/NA/yes. That will show you the expected reception at your location. It will also give the current channel allocations so you can do a manual retune on each channel.



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MikeP's 2,039 posts Platinum Platinum GB
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