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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 by on UK Free TV

There are several different type of interference that cause problems. This page deals with the situation where:

  • Freeview reception is perfect or near-perfect most of the time
  • Several channels are missing, but they are all on the same 'multiplex'
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, www.ukfree.tv link icon 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 www.ukfree.tv link icon My Freeview reception and looking under the "Free RF channels" section.

Non-wideband aerial in some areas

In some places you will need a www.ukfree.tv link icon 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 www.ukfree.tv link icon My Freeview reception.





Your comments: most recent posts are at the bottom

firstFirst comments prevEarlier comments  ◊ 

Your comments are always welcome. Please use the form below to add your thoughts or questions to this page. We will get back to you as soon as we can.

Gary
Tuesday 29 May 2012 8:40AM Sevenoaks
I receive Freeview from Crystal Palace, and before switchover CH22 was the weakest signal and gave most problems. Now after switchover I see CH25 is showing the weakest signal strength. I am curious as to why this is.

I am also experiencing very short but frequent freezing of the picture, sound is not affected though. These little "blips" are very brief and only last about a second but are extremely annoying. Does anyone have any suggestions?
Dave Lindsay
Tuesday 29 May 2012 11:16AM
Gary: It could be that the signal is now on the high side and that a little attenuation may help you. See:

www.ukfree.tv link icon Freeview signals: too much of a good thing is bad for you | ukfree.tv - independent free digital TV advice
Robert
Saturday 16 June 2012 5:49PM
Gary: If you’re looking at the signal strength although important, Signal Quality (or bit error rate) is the more important for reception. It is an indication how much work the digital error correction the tuner has to apply to the data stream. Less error correction or better quality is what you are after.

There would have to be very extensive work to support DSO with probably a lot of hardware going live for the first time on the 4th and 18th April 2012. It is described on the Arqiva website as a man turning a big lever from ‘on’ to ‘off’ in one hall of equipment moving to the hall next door and turning another big lever from ‘off’ to ‘on’. Analogue went off on came the new Digital Mux(s). All I can say it must a moved very very slowly between the halls.

Frequent freezing would suggest that in some cases, the data is so badly damaged it gives up trying to produce a picture. The data is no longer correctable; it unrecoverable and we have gone way beyond an error pixel or two.

During these periods of freezing, you have a reception problem. Getting the best signal you can into aerial would a good start. You don’t say how close to CP you are and my own reception problems are documented under the interference section.

Good Luck
Chris
Friday 22 June 2012 9:33AM
Since retuning the TV on the 13th, all mux channels are OK except channel 55, which initially shows c. 50% signal strength and 100% quality but quickly drops to 0% for both (in stages of about 20% per second) and then stays at 0% until I reselect channel 55.

The PVR has no similar issues, and has a steady strength and quality for channel 55.

(Aerial lead is first into the PVR, and then RF out from there to the TV RF input)

Is this likely to improve on the next retune on the 27th?
Richard Randall
Thursday 12 July 2012 11:38PM
Is anyone experiencing interference to the ITV Freeview channels in postcode SO15.
Richard
Richard
Friday 13 July 2012 9:51PM
Ha, turns out the HDMI and RF cables must have been moved during cleaning and were too close together. All fine now.
Richard
Kathleen
Monday 3 September 2012 5:15PM
my freeview freezes when the neighbours use gardening equipment or heavy machinery what can I do to stop this
Mark Fletcher
Monday 3 September 2012 6:35PM Halifax
Kathleen.Without a full postcode preferably or a nearby location as such,we cannot be of any useful help to you.
Mark Fletcher
Monday 3 September 2012 6:36PM Halifax
Richard Randall.SO15 area.I would look up inversion effect as a likely culprit.
Mazbar
Monday 3 September 2012 7:51PM
Kathleen: There are a number of reasons that cause your type of problem but the two main ones are broken coax if the cable comes straight from the aerial to the tv have a look at the aerial plug for rust or water the other cause can be an amplifier picking up the interferance this can be harder to solve this needs a full check on your system hope this helps
John Cameron
Thursday 6 September 2012 10:11AM Isle Of Islay
On the last occasion, Sept 4th. that I "lost" the BBC A group + radio it turned out that engineering had been in progress.
At other times, however, I lose this group (only) during, I have noted, persistant rainfall. (water on slate roof).This may indicate the BBC group signal is weaker - could this be the case? Thanks for your attention.
B. O'Neill
Sunday 9 September 2012 10:27AM
We receive our signal from the Divis transmitter in Belfast. Until a month ago we could receive all the Freeview channels perfectly. Then all the programmes on channel 33 disappeared, reappeared and finally disappeared. We have a new digital aerial, have cleared the channel list completely and then rescanned but still no channel 33 programmes. The aerial is going straight into the back of the TV. As all the other channels are great why is channel 33 having problems?
Dave Lindsay
Sunday 9 September 2012 2:06PM
B. O'Neill: There has been engineering work taking place in preparation for switchover. We do not know what this was/is, but it is a possibility that it was something that may affect reception, particularly in areas where the current low-power signals are marginal (i.e. "only just" good enough).

It is possible that whilst the other channels are perhaps "only just" above the threshold required to produce a picture, that C33 is now "only just" below the threshold.


There is no such thing as a "digital aerial". Aerials work based on the frequencies of the signals that they are installed to receive.

In the days of four-channel analogue it was commonplace for aerials to be fitted that are most sensitive to the group of channels/frequencies used by the desired transmitter.

For Divis this is "Group A" which is the first or lowest third of frequencies used for TV. Before switchover all digital channels are within Group A except Mux C which is up on C48. In some cases (at some locations), the lower power pre-switchover digital signals may not be strong enough to be received (or "heard") by aerials that are sufficient for analogue. Where this is the case, replacement with a more sensitive aerial may yield reception of those digital channels. However, it is expected for Divis that, generally speaking, (Group A) aerials installed for analogue will work for digital after switchover on 24th October. This is because all of Divis' channels will be in Group A. The stronger signals should also mean that aerials that are more sensitive (higher gain) that were installed pre-switchover aren't necessary.
philb
Wednesday 12 September 2012 9:16PM Bromsgrove
Hi - my postcode is B61 0JG. I should be able to receive transmissions from the transmitter in Bromsgrove at Worms Ash. However the aerial installer before switchover said I was getting a signal from Malvern but at least that worked fine. I have two cheap digital boxes and they both have the same problem. If I retune one (Goodman's) you just get what it gives you but the other (Grundig) is a choice of Gloucester Central, Gloucestershire West, West and West Midlands. All four settings tell me the transmitter is in Gloucester. I struggle with UHF 47. Tonight I can pick up nothing from that others times I generally get a poor picture. Most other frequencies esp. BBC, ITV and C4 are fine so I think the TV, box, and aerial are OK. The problem looks to be the signal I am picking up. Advice apprecaited. More info supplied if required.
Malcolm Watson
Saturday 15 September 2012 10:37AM Coalville
Malcolm Watson
I have spent a considerable amount of money on new digital TV's and arial system(signals received from Sutton Coldfield transmitter).The TV's have built-in Freeview receivers.I have read all the possible causes of loss of signal reception, but the fact remains that I am not getting the sevice I expect or am paying for. Over the last month or so the situation has become much worse. My neighbours are also having regular problems with reception. What, if anything, is being done to correct the problem.
Vik
Sunday 23 September 2012 8:28PM
Borehamwood, Herts. (23/09/12). Since the suggested retune last week the TV no longer receives any HD channels and all those on C25 have interference. Have retuned (manual and auto) a couple of times since but still no joy. Had enjoyed HD prior to this on the TV. The separate digi box recorder is not affected and all is fine and yet it runs off same aerial point (the TV is primary connection with dig box connected via a splitter). Any ideas? Think Crystal Palace is the transmitter.
Sarah Bramley
Friday 28 September 2012 12:41PM
We are in the Tyne Tees area and phase 2 of the switchover happened on the 26th Sept. We have now lost Really, Dave, 5*, 5 US, Pick TV and Quest. We have unplugged the aerial and re-tuned, then re-tuned numerous other times, done a factory reset on the recorder box, etc, but to no avail. Any suggestions?
Sarah Bramley
Friday 28 September 2012 12:41PM York
Forgot to say, my postcode is YO10 3EY
Dave Lindsay
Friday 28 September 2012 12:54PM
Sarah Bramley: You may need your aerial replacing if it is a group A one put up in the days of four-channel analogue. See here for an explanation:

Bilsdale (North Yorkshire, England) full-Freeview transmitter | ukfree.tv - 10 years of independent, free digital TV advice

Before you do this, if your receiver has a manual tune facility then use it.

For COM4 multiplex which carries ITV3, 5*, 5USA, QUEST and others, tune to UHF channel 43.

For COM5 multiplex which carries Pick TV, Dave, Really and others tune to UHF channel 46.
Ian Baty
Sunday 14 October 2012 10:48AM
I am having problems receiving channels on the D3+4 frequency, all other channels are fine. I live in Newcastle Upon Tyne. Is there a problem at the minute or can i do anything to the set to retrive viewing capability of these channels? I have tried a full Auto Scan without any luck already and have a TV with built in Freeview.
Many Thanks Ian.
Dave Lindsay
Sunday 14 October 2012 10:54AM
Ian Baty: There may be a number of transmitters that can be received from and automatic tuning functions are in no way infallible when faced with multiple transmitters.

Have you confirmed that it is tuned to the D3&4 broadcast from your transmitter?
Ian Stewart
Tuesday 23 October 2012 8:02PM Dundee
Why am I unable to get the channels (such as Film on 4) in Dundee from the craigkelly transmitter. When I do get them that are blocky and the sound is just sqeaks. Funnily when I tune into Film4 in the early morning and the teleshopping is on the signal is almost perfect. Also my Sony Bravia shows a "no signal" message whereas other "simpler" tvs in the house get the broken picture described above. We have used the same aerial trained on Craigkelly for about 6 years and it was only sometime in 2011 that we lost Film4, etc., which till then were perfect. Help please.
Anthony
Monday 29 October 2012 4:53PM
Hi
my postcode is BT221LJ

I have a hd panasonic digital tv.

i have 2 ariels one pointing to divis and one pointing to co louth.

the co louth ariel feed is passed through an vhf uhf inverter bot feeds are the combined in a 21-37 38-68 combining unit and then passed through a 4 output amplifier.
before switchover i had a poor but watchable quality picture from rte

At present I am recieving all digital channels in good quality apart from the rte ones.

I was hoping I could now get these from divis/black mountain rather than having to purchase a saorview box. Any ideas how I might get the rte channels
Dave Lindsay
Monday 29 October 2012 5:11PM
Anthony: Your Panasonic TV will probably need to a "Freeview HD" one. HD ready means that it will show HD pictures but doesn't have an in-built Freeview HD tuner. Full HD means that it will show the highest resolution HD pictures and doesn't necessarily mean that it will receive HD signals. Knowledge of the model number would allow us to check the specification.

Manually tune to UHF channel 52. This is the channel used by Clermont Carn, Co. Louth which I assume your RTÉ aerial is directed to. If the manual tune screen has a setting for DVB-T and DVB-T2 modes, then select the former. A Freeview HD receiver will probably be needed to receive Saorview.

If this doesn't work and you decide to attempt reception of the NI Mux, then the "inverter" (diplexer) you identify will have to be removed. This is because the NI Mux broadcasts on C39 which is therefore above the range allowed from your Divis aerial.

I say "attempt" because the Digital UK Postcode Checker doesn't "think" that you are in a good area. These things are never ever perfect and therefore should be taken with a pinch of salt. However, it may be touch and go as to whether it will work (fingers crossed though).

The NI Mux carries only RTÉ One, RTÉ Two and TG4, all in standard definition.
Anthony Murray
Wednesday 31 October 2012 8:54AM
Hi Dave
my panasonic is model TX-P42C2B
I thought it had a hd tuner
My second digital HD tv at the minute connected to sky is a sony KDL-40V4000

are eithier of them a hd tuner

Many thanks for your help
Anthony
earlier post copied below

earlier

Anthony
Monday 29 October 2012 4:53PM
1 day ago
Hi
my postcode is BT221LJ

I have a hd panasonic digital tv.

i have 2 ariels one pointing to divis and one pointing to co louth.

the co louth ariel feed is passed through an vhf uhf inverter bot feeds are the combined in a 21-37 38-68 combining unit and then passed through a 4 output amplifier.
before switchover i had a poor but watchable quality picture from rte

At present I am recieving all digital channels in good quality apart from the rte ones.

I was hoping I could now get these from divis/black mountain rather than having to purchase a saorview box. Any ideas how I might get the rte channels
Dave Lindsay
Wednesday 31 October 2012 11:27AM
Anthony Murray: It looks as though these two TVs don't have a HD tuner in-built.

I couldn't find the official specifications page on the Panasonic website, but I did come across listings on Play.com and eBay for it and both said that it is "HD Ready". This means that it won't receive HD signals, although I think that some people may have bought such sets prior to HD signals coming on air (i.e. before switchover) with the thinking that they will be "ready" to receive HD when it comes on air.

The specs on the Sony website say that it is "Full HD" rather than "Freeview HD". Full HD means that it will show HD pictures to the highest resolution of 1080p:

www.sony.co.uk link icon http://www.sony.co.uk/pro…#tab

The Sony website also says that the digital tuner supports MPEG2 so it won't show pictures with Saorview (as this uses MPEG4).

Freeview HD receivers are expected to work with Saorview.

Try a manual tune on C52. The TV may tune it but show no picture but will nonetheless indicate if you can receive Saorview.

In order to receive the NI Mux from Black Mountain on C39 you will probably need the diplexer removing (and hence the Clermont Carn aerial disconnected).

Realigning the Clermont Carn on Black Mountain "may" work (this includes retaining the diplexer), although as the diplexer "splits" at C38, adjacent channels are attenuated quite a bit so this could perhaps be doubtful:

www.aerialsandtv.com link icon Online TV Splitters, Amps & Diplexers sales

In a stronger signal area, this attentuation might not have been such an issue.
Lesley Gyford
Saturday 10 November 2012 4:30PM
Until last weekend we had very few problems with our freeview. Last weekend all the channels disappeared and I had to retune. since then we have not been able to get the HD channels and the PSB2 Mux keeps coming in and out, often dissappears completely or is so badly pixelated we cannot watch any of the channels. I have a Humax Fox T2 HD box, our aerial is pointing towards the Nottingam transmitter. I have to manually tune otherwise I get interference from Waltham transmitter. This is getting tiresome - does anyone know why this is happening and how I can fix it?
jb38
Saturday 10 November 2012 7:30PM
Lesley Gyford: Anyone advising on a problem such as yours cannot do so with any level of accuracy without having knowledge of your location, this in the form of a post code or one from somewhere nearby (e.g: a shop) as only then can the reception predictor be accessed, this facility giving an idea of the signal levels expected in your area.
Andrew
Monday 24 December 2012 4:08PM Wallingford
I can not receive itv1and channel 4 and the other stations on the same multiplex. Has been fine for years but channels are pixelated and unwatchable? Have tried both auto and manual retunes.

This has happened in the laste few weeks. Postcode is ox10 9hp.
jb38
Monday 24 December 2012 6:53PM
Andrew: Oxford is indicated as your best bet for reception although Crystal Palace and Hanningtom are also shown as being possible, but if you are receiving from Oxford then try manually tuning in mux Ch60 as the programmes mentioned as missing are on that transmitter.
Mazbar
Monday 24 December 2012 6:59PM
Andrew : as you have said you have allready tryed a manual tune if your coax comes straight from the aerial to your tv or stb have a look at the coax plug for rust or a milky white this could mean your coax is damaged this can start problems on one channel befor affecting others. Trees can also affect only one channel more than others .
Andrew
Tuesday 25 December 2012 9:51AM Wallingford
Thanks to both jb38 and Mazbar for taking the trouble to respond on Xmas eve. I discovered that my immediate neighbour lost the same channels a few weeks ago but was able to recover them a day or so later. He has a rather recent freeview tv whilst I am still using a set top box which is 4 to 5 years old. I will check the aerial as well which is also not new.

I will try and let you know if I resolve it ...or not!
jb38
Tuesday 25 December 2012 12:27PM
Andrew : Yes thanks for the update, but with regards to the mux transmitter used by these programmes, its most likely still there in your boxes memory but is sitting at a level just under the reception threshold for your receivers tuner hence why you are unable to see anything, and this being something you can check by carrying a signal strength test, because provided that you have not carried out a retune (which might lose it) then it will still give an indication of strength / quality even on a blank screen.
Dave
Wednesday 9 January 2013 3:06PM
We're receiving from Pontop Pike. As of last night 8 Jan, our 2 yr old Panasonic TV reports "No Service" on any of the previously perfect CH50 stations (10-ITV3, 38-Quest, etc). They still appear in the Program Guide & Signal strength and quality are both maximum; I've tried resetting, retuning, and confirmed that everything's still tuned to Pontop Pike.
Annoyingly, our Humax PVR (on the same aerial) is unaffected, (I've disconnected it to eliminate possible problems). Our two other small TVs (Samsung and Asda cheapie) are also still working perfectly.
A neighbour with a similar Panasonic has exactly the same problem.
Any ideas?
Dave Lindsay
Wednesday 9 January 2013 3:25PM
Dave: See the page for Pontop Pike where two other people with Panasonics have reported exactly the same issue with the same channel.
Dave
Wednesday 9 January 2013 3:56PM
Thanks Dave, I've just spoken to the retailer (John Lewis) who spoke to Panasonic while I was on hold who, in turn, said they've had several complaints about this; I was assured they'll be looking into this and there may be a s/w update in the near future.
Perhaps this post could/should be moved onto the Pontop Pike page?
Dave
Dave Lindsay
Wednesday 9 January 2013 4:12PM
Dave: I have posted a link on the Pontop Pike page referring back to your posting.
Mike
Wednesday 13 February 2013 2:53PM Loughborough
I receive my tv transmissions from the Waltham mast. My Sony tv on autotune finds all channels but ITV is for Lincolnshire not East midlands resulting in incorrect local news programs and pixellating (no pixellation on other channels) Can anyone tell me correct frequency to manually tune ITV to sort this problem?
Dave Lindsay
Wednesday 13 February 2013 3:04PM
Mike: ITV from Waltham is on C54 (737.8MHz).

The other alternative is to have the aerial unplugged for lower channels which will prevent it from finding the East Yorks & Lincs signal from Belmont. Get the aerial in at about 50% or C45.

Once you've done this, go to the manual function and add C29 (538MHz) which is COM4 (ITV3 etc) from Waltham.
Trevor
Wednesday 27 February 2013 11:25PM Banbury
Ox17
Film4 etc (com6/arqB) have variable signal quality throughout the day, from watchable to 'no signal' on both my Sony TV and BT box. The aerial is new and the signal amplified for house distribution.
Is this one type of single frequency interference or should I be looking elsewhere for the problem?
Thanks
Liz Biron
Friday 29 March 2013 8:50PM
Hi,

Despite endless factory retunes, we have had no reception of any BBC channels in the centre of Taunton since the retune. We are also missing some but not all channels from the multiplex with ITV3, five star and five USA on, but not all becuase we do have E4 channel 28. I am absloutely dumbfounded by fact that nothing has yet been done about it and how little we are being told - or may be that's going out on BBC channels! One of our neighbours has all channels, another like us is missing loads. Is the issue with our aerial? if so, why weren't we warned that this will be a problem. We had perfect reception on all BBC channels before the retune.

Please respond with likely timescales for resumation of normal service, else what we need to do to get reception again.

Unbelievably pissed off.
KMJ,Derby
Friday 29 March 2013 10:03PM
Liz Biron: Can you give some details about your aerial? Is it a communal aerial, or if it is your own is it a single aerial connected directly to the receiver, or is it combined with a second aerial in order to receive a relay plus a main transmitter or two different main transmitters? If you are trying to receive from Mendip you are missing C48 and C49 for some reason. If manual tuning is available on your tuner try entering each of the missing frequencies, taking note of signal strength and quality for each before storing any channels, that is, if any are found!
Chris Johnson
Saturday 27 April 2013 3:29PM
Dear UK Free TV,
I own a Humax PVR 9150T. Generally it's great. I have a problem with poor quality on some channels. Eg ITV4. The signal strength on all channels is about 75%. BBC1 etc are 100% quality. ITV4 Etc cycles between 10% and 100% quality. The same signal comes out of the humax box into the TV and the quality is fine with the TV.


Dave Lindsay
Saturday 27 April 2013 3:36PM
Chris Johnson: If this is a request for help then as it is a signal related issue you will have to provide an idea of your location, preferably in the form of postcode or nearby postcode (such as that of a shop).

The Commercial (COM) channels which carry ITV4 and others do not have as good a coverage as the other Public Service (PSB) ones which carry BBC, ITV, Channel 4, Channel 5 and others. This is the reason why knowledge of your location is imperative.
tim
Saturday 18 May 2013 2:57PM Norwich
we live in east harling (tacolneston transmitter) and use bt vision, but since 1 May, when i understand some frequencies changed at tacolneston, we haven't ben able to get a proper picture on UHF channel 39, which now carries all the ARQB channels, including film 4 and sky sports 1 and 2 (prior to 1 May, all was fine). We have no vcr, games console, thus ruling out local band interference, so guess we are going to have to buy a wideband aerial to get the channels back? am i right?what is the likely cost of installation and is it guaranteed to work?
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