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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
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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

Comments
Thursday, 25 August 2011
J
jb38
sentiment_very_satisfiedPlatinum

9:21 PM

Stephen F: But that's the very point I am making, being, that your box doesn't show any interference when receiving channels from the Mux still on the original 2k operating mode, whereas it does with channels which are on a Mux now operating on the 8K mode, such as the BBC and Ch5 etc.

8K is known to cause a variety of problems on some older equipment, these ranging from either not working at all to erratic performance if it does, so I only take account of the programme channels you mention to cross check them with the technicalities of the multiplex they are on.

The main other possibility for the problem, that of the signal being too strong, has already been discounted when you tried the set top aerial, this only leaving the possibility of 8K incompatibility as the main suspect, that is unless your box has developed some other odd fault, which I doubt it has. Local interference also being excluded as your TV works perfectly OK on the same aerial.

In other words, "you" would have discounted the 8K problem theory if you had seen the same type of interference on programmes using Mux Ch49, which you say you haven't done.

Needless to say "if" 8k is indeed the cause then you cannot really do anything about it, as its a software issue.

PS: Just spotted your latest posting when I scrolled up the screen. Although these can cause problems, however you having witnessed the interference using a set top aerial means that the problem is nothing connected to the aerial system.


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jb38's 7,179 posts GB
S
Stephen F
9:33 PM
Colchester

jb38: Thanks I think you are right. I will contact BT and see what they can do for me. Thanks for your help.

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Stephen F's 10 posts GB
M
Mike Dimmick
sentiment_very_satisfiedPlatinum

11:03 PM

Stephen F: Channel 5 is carried on the D3&4 multiplex on C41 (634 MHz), while the BBC channels are on the BBC A multiplex on C44.

What sort of interference are you seeing? For digital interference you would see picture break-up - blocks or lines tearing, or a frozen picture with moving blocks - and/or breaks in the audio (possibly accompanied by clicks). If you're seeing snow, as you would on analogue, this would probably be cross-talk on the SCART connection - try a different SCART lead. If that doesn't help, it could be cross-talk inside the receiver and you should have the box replaced.

If the BT Vision box itself has an RF modulator, and you're tuning the TV into the box as if it were an analogue TV station, try selecting a different channel for the modulator, or using a SCART cable.

If it was a problem with not supporting 8K mode, I would expect it to not be able to tune in BBC and ITV channels at all, not just have interference.

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Mike Dimmick's 2,486 posts GB
Thursday, 1 September 2011
J
jb38
sentiment_very_satisfiedPlatinum

5:17 PM

jg: In your particular location it will nearly be impossible to receive Waltham without doing so by manually tuning in the various Mux channels involved, that is unless your TV has a "region" facility within its tuning menu, if it has have you tried using that?

The reason for your problem being that its likely you are picking up Sutton Coldfield on some channels and Waltham on others, as Sutton is shown as being not too far off the same reception level as Waltham.

To manually select the channels you first of all blank out everything stored in the memory, this done by carrying out a re-scan without the aerial being connected, then once done re-connect the aerial and manually tune in the channels required using the add channels facility, storing what's received if not done automatically by the set.

Waltham's Mux channels being: 29 - 54 - 56 - 57 - 58 - 61.

(Note: Ch 29 is presently on low power)


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jb38's 7,179 posts GB
Tuesday, 6 September 2011
S
sue
11:32 AM

Hi there
Bought new tv in June..Had the old fashioned aerial on the chimmney, this picked the bbc and itv channels as well as she shopping channels, quest, challege,5*, itv2+1, itv3 and lots of radio.Other channels came up but did not tune.
After a strong wing the black disk on the aerial with the cable attached broke, so bought a new high gain,wide aerial, this was ok for 1 day. I can now only get some BBC, and some ITV, the other channels do not even come up on the screen. I have re-tuned.
Any thought. Thanks

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sue's 1 post GB
Wednesday, 7 September 2011
L
louise
6:41 PM

hi all
im hoping someone can help me. i am having problems with my freeview box. as of last week i lost all the channels on 'group c' how do i go about getting them back? i have re-tuned about 20 times now and they are still missing. also im having signal problems from time to time on some of the channels. i have never had any problems before. i live s42 postcode.

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louise's 4 posts GB
J
jb38
sentiment_very_satisfiedPlatinum

7:26 PM

sue: Its impossible to assist with any reception query when your location (post code) has not been provided.

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jb38's 7,179 posts GB
J
jb38
sentiment_very_satisfiedPlatinum

7:30 PM

louise: The S42 post code area indicates that (in theory) a number of different stations can be received, so in the interests of accuracy you really have to provide a full post code.

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jb38's 7,179 posts GB
Friday, 9 September 2011
L
louise
4:45 PM
Chesterfield

JB38 my postcode is s42 5jw. i have retuned again and still cant get the channels in 'block C' (on the table above)
how do i get them back?

link to this comment
louise's 4 posts GB
J
jb38
sentiment_very_satisfiedPlatinum

9:41 PM

louise: Well on having a look at the trade reception predictor, although Sheffield (@ 15mls) is showing as a possibility for reception as well as Chesterfield (@ 7mls), I feel that its more likely to be Emley Moor you are receiving from, the problem there being that you are not forecast as being able to receive "C" (ArqA) until the 21st of this month when switchover stage 2 takes place.

This said taking it that when you say block "C" you are meaning the one containing programmes like - Pick TV / Dave / E4+1 etc? these presently being on Mux Ch50 from Emley but changing to Mux Ch52 on switchover.

Although a long shot, you could try a manual tune on Sheffield's Mux Ch45 or Chesterfields Mux Ch46 to see if anything comes up, as the programmes referred to are on the two channels mentioned.

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jb38's 7,179 posts GB
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