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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
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, 19 April 2012
Peter Danckwerts
6:42 PM

Thanks. It comes down to what my wife asked and what the salesman told her and I don't suppose she asked the right questions.

However, there is definitely misselling. I saw an ad for this model yesterday and it was advertised as 'Freeview HD' (OK, it is HD and it is Freeview, but 'Freeview HD' would suggest to most people that it had a Freeview HD-compatible tuner). I think in general those selling these televisions are only too glad to take advantage of customers. Also, I can't see why anyone would knowingly buy an HD TV in the UK with built-in Freeview tuner which didn't decode the HD signals. If they wanted an HD TV to use with cable, for instance, they'd have no need for a Freeview tuner at all.

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Peter Danckwerts's 3 posts GB flag
Peter's: mapP's Freeview map terrainP's terrain plot wavesP's frequency data P's Freeview Detailed Coverage
Friday, 20 April 2012
9:12 AM

Mux D is now fine in OX10 on PVR as well as TV.

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Ian's 3 posts GB flag
Sunday, 22 April 2012
1:43 AM

Hope you can help me - and hope this is the right place to put my query.

I've been using a digital set top box in my rented room in a shared house for a while - it's a fairly basic Sagem box, not sure of a particular model - I inherited it from a friend who didn't need it a few years ago. It's plugged into my TV with a scart and uses a basic metal hoop indoor aerial (there's no aerial connector in my room to the aerial on the roof) - but I've never had any problems at all with my freeview reception.

Since the morning of the switchover this week I've not been able to receive any of the channels on Multiplex's 4, 5 and 6. I'm in Streatham (SW16) about four miles from the Crystal Palace transmitter, and I've been reading conflicting information about what might be causing this and what to do about it...

I've done factory resets and channel searches every day to see if the problem would resolve itself, with no luck. Checking my signal information on each channel - C23 and C26 both have good signal strength in the mid-60% and excellent quality (91-97%), but C22, C25 and C28 all fluctuate dramatically and generally remain in the red "poor" zones anywhere between 50% and 80%, even though the signal strength for all three is also in the mid-60% - green for "good".

Judging from that info do I need a signal booster? A new aerial? A signal dampener? A new set top box? I'm looking to get a freeview+ or freesat+ box anyway, but I'm hesitant to do anything until I know what's happening with the signal in my room in case the same issue arises with a new box.

All help will be greatly appreciated. Thanks!

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Dominic's 3 posts GB flag
Dominic's: mapD's Freeview map terrainD's terrain plot wavesD's frequency data D's Freeview Detailed Coverage
12:10 PM

We are served by the Crystal Palace transmitter here near Orpington and have a new Humax PVR.

Before the switch off of BBC2 analogue all was working well. When it was switched off all channels deteriorated, the reception being sometimes better from both Cambridge and Anglia. We decided to wait until the switch off on the 18th to see if things improved.

During the day it is fine, 81% signal strength on all channels and 100% quality, but in the evening, although the signal strength stays the same, the quality fluctuates continually between 40% and 100%, making it almost unwatchable.

I have checked your site for an answer. We have switched off all lokley culptites suich as central heating to no avail.

Does anyone else have this problem?

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Catherine's 2 posts GB flag
Robert Dallenger
2:58 PM

I've recently bought a Humax PVR to replace my old Pace Twin. I had it installed for a week via RGB Scart which appeared to be ok, although I did not test for long the HD Multiplex (BBCB). Since switchover, I have just bought an HDMI extender to make use of these channels on another tv in a different room. The extender uses cat5 cabling.
The problem I am having is with all the HD Multiplex pictures either breaking up or disappearing completely. When the Humax video format is set on 576i or 576p, ALL is ok, but as soon as I select either 720i/p or 1080i/p I lose the signal. I can however play back recordings OK from those channels, which I had recorded pre-switchover. I have tried plugging my PS3 into the HDMI extender and that works fine too, so I don't believe it is the HDMI extender that is at fault here. I believe it could be a problem with the downlead from the aerial splitter as the one which goes to the living room appears to be fine because when plugging the HDMI directly into the living room tv and using the aerial connection in there, there is no loss of signal.
I have remade the connection, but the problem still persists. Can anyone tell me why though, it is ok in 576i/p and it is also ok for a minute or two in 720 or 1080. Could it be an overheating problem with the Humax?
I'm usually pretty good when it comes to this stuff, but this one has me stumped. My next move is to try my Panasonic Freeview PVR on that same downlead to see if the same thing happens on that.
All other frequencies appear to be ok, although some do give a lower quality of signal than others. It is a wideband aerial fitted a couple of years ago with new cabling.

If anyone else can input anything into this problem, it would be much appreciated.

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Robert Dallenger's 3 posts GB flag
Robert Dallenger
3:05 PM

Robert Dallenger: Forgot to say that I am on the Crystal Palace Transmitter.

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Robert Dallenger's 3 posts GB flag
Robert Dallenger
3:08 PM

Catherine: Is this happening on ALL frequencies or just one in particular? I'm having a similar problem with a Humax PVR myself post Crystal Palace switchover but mainly on HD Channels.

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Robert Dallenger's 3 posts GB flag
9:22 PM

Hello, just moved into a new house, we have Sky set up in the living room and we were given a gift of a digital TV to put in the kitchen. We have an aerial socket so plugged it in and got no signal, tried the same in bedroom socket and no signal. Went into the loft and can't see an aerial lead or booster went out and bought an internal aerial and low and behold the TV is still not receiving any signal. Can you help?

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Dave's 1 post GB flag

11:09 PM

Dave: Its quite impossible to offer any advice on this problem without having knowledge of the location involved, this preferably in the form of a post code or one from nearby (e.g: a shop)

But though when you went into the loft and found no aerial, did you then run a new coax cable from the loft to the kitchen?

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jb38's 7,179 posts GB flag
Wednesday, 25 April 2012
4:03 PM

Robert Dallenger:

We don't have HD but the problem is on all channels. I don't watch much during daytime but find the problem also exists then to a lesser degree.

Sometimes it is better to watch the transmission from Cambs and Beds.

I see a Humax update is due to be transmitted over the air at the end of the week. I don't suppose this will help.

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Catherine's 2 posts GB flag
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