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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
Saturday, 15 January 2022
C
christopher beacroft
1:43 PM
Matlock

We have intermittent sgnal ar de44ll is there a fault or is it going to be prmanent

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christopher beacroft's 1 post GB
Saturday, 19 March 2022
P
p griifin
5:23 PM

Channels 1 to 5 are void on my freeview and the picture somtimes breaks up. Also the local BBC 1 news is not available on 1 or 101

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p griifin's 1 post GB
C
Chris.SE
sentiment_very_satisfiedPlatinum

9:22 PM

p griifin:

It's current weather conditions - there is some Temperture Inversion/Tropospheric Ducting which will enable signals from more distant transmitters to be more easil;y received - and that will in a few instances result in interference to normal reception (you'll see the sort of thing you have with Signal Strength varying considerably and Quality dropping, often to zero)......"
FYI, such transmitters can be in the UK or Europe.

Both Freeview and the BBC have got warnings on their Update & Alerts/Works and Warning pages about possible disruption to reception.

This type of interference can be frequency dependent and/or depending on where the interfering signals are coming from, the identical channels to your normal ones may be different, so even if a broader spectrum of frequencies is affected, not all you reception will be disrupted. Sometimes they all could be.
The interference can last for seconds, minutes, hours even longer and can come and go seemingly at random.

The general advise is to NOT retune, as this invariably may cause you to lose your correct tuning and/or become incorrectly tuned to another transmitter whose signals can disappear when conditions change.
If you have become incorrectly tuned (check the UHF channels in your TV Tuning section) then it's best to try manually retuning each of your normal transmitter's UHF channels. You may have to try several times if interference is present.

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Chris.SE's 3,174 posts GB
Tuesday, 22 March 2022
S
SteveK
2:42 PM

Chris.SE: Aerial fitter says my installation is fine and cannot understand why C46 is rubbish considering all other frequencies are tickety-boo. Hey ho!

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SteveK's 15 posts GB
Wednesday, 23 March 2022
C
Chris.SE
sentiment_very_satisfiedPlatinum

12:24 AM

SteveK:

Hmm, is it the same fitter that installed it or a different one? Where is your aerial?
What precise checks did he do?

You didn't reply to my previous response, and didn't post any signal strength and quality (or error) figures as suggested. Has the problem been continuous or has it been OK on some weeks or even days during some weeks? Has any good reception been consistent with good weather? How is it now?

I've just done some further checking and the Heathfield transmitter was on Planned Engineering for some extensive periods, and is currently listed AGAIN w/c 21/03/22 ! so I'm not necessarily convinced all is well at the transmitter, but again it could depend on what checks the fitter did!

Did the fitter make any comment about Planned Engineering/Transmitter maintenance?
Previous listed dates are w/c 17/01/22 to w/c 07/02/22; and w/c 28/02/22 to w/c 07/03/22, and now w/c 21/03/22. The listed possible effects are "Pixelation or flickering on some or all channels" which can mean reduced signal.
But without further detail, I'm not sure what further constructive suggestions I can make.

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Chris.SE's 3,174 posts GB
Saturday, 26 March 2022
S
SteveK
11:59 AM

Chris.SE:
Same company as originally fitted. Aerial on mast/pole above roof. He checked feed behind TV with meter and again in loft above signal splitter. Same result - C46 rubbish. Visual inspection of aerial from ground. Indicated that tinkering around with alignment might cause deterioration of other channels. This particular local area has always had dubious reception and changes from house to house. Lots of aerials have now disappeared and satellite dishes are to the fore. My immediate neighbour never watches the C46 stations - only 1, 2, 3, 4 and 10 they say (......they have an HD TV!)

C46 reception has been variable but continuously rubbish. Sometimes that signal has some strength but zero quality.......according to TV's signal information. Second TV does not have quality indicator, just strength.

Reception of C46 improved with bad weather, if anything.

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SteveK's 15 posts GB
C
Chris.SE
sentiment_very_satisfiedPlatinum

5:14 PM

SteveK:

Well, I'm afraid to say I think he should have got up on the roof and inspected the aerial connections at close quarters to ensure that rain wasn't getting into the connector box and there was no corrosion.
I have noted that you've had problems with C47 as well as C46 in the past, this I'm afraid smacks of the POSSIBILITY of a bad connection or water in the aerial connector and maybe coax. The consequences of which are that "standing waves" can occur in the cable - this is frequency dependant and it in effect will cancel out some/all of a signal at the given frequency. This may not be the cause of course, but it's a possibility that SHOULD have been eliminated from simple inspection.

There is something you can do, have a look at the connector on the downlead from the aerial into your booster. If water has got into the cable, it may (and often does) work its way down to the connector. If there is any sign of any corrosion or the slightest dampness of the cable at that point then this is the likely cause.
Of course, now we've had this sustained period of dry weather, any damp may have disappeared, but any corrosion will not - detected by any "greeness" around or inside the plug or the end of the cable, remove the connector if need be, to inspect the cable.

Just to add though, there has been transmitter maintenance at Heathfield, the BBC have reported "From 10:01:43am to 11:11:54am on 22nd Mar 2022, BBC A, Low power due to essential engineering, and
From 10:02:11am to 11:12:12am on 22nd Mar 2022, BBC B HD, Low power due to essential engineering.
I would guess other multiplexes may have been similarly affected (the BBC only report on their own).

I guess you've recently got Freesat from your other post, good luck with it, I'll pop a post over there for you.

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Chris.SE's 3,174 posts GB
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