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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
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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

Wednesday, 2 February 2011
4:00 PM

hello Brian, can't believe the amount of help you have provided to people on this website - you must be commended!!

Hopefully you can help me.

Dont know how old my aerial is. I've done the check on analogue teletext p284 & all the white bars are fine. It tells me i'm getting a signal from Waltham. My postcode is NG8 3HL. I have a new tv with built-in freeview. Previously i had a freeview box & i have always had missing channels.

Current freeview has missing channels block 2 & 3. Previous freeview could receive ITV, CH4 etc, but it wasn't worht watching as it was very very choppy & intermittent.

Are you able to point me in the right direction or advise if i need a new aerial, or do i need to do something else? Got someone here this week with a long ladder so i can sort it if need be. I dont have a booster or anything. I've just removed connections to external devices & retuned the tv, but the channels are still missing.

Do you know if i need to point my aerial to the nottingham one? The cable from teh aerial is split between 2 rooms, the 2nd one isn't a digital (but will be in future...)

If i do need a new aerial, i guess it's a wideband i need?

Thanks for any advice :)

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DG's 3 posts GB flag
DG's: mapD's Freeview map terrainD's terrain plot wavesD's frequency data D's Freeview Detailed Coverage
4:48 PM

I went into my sky box and the Rf was set as in the guide 68 and off. I didnt know what to set it to so I changed the RF channel to random channels and it didn't make any difference. Now, on the tv upstairs there is picture/sound break up even after turning off all the equipment downstairs.

Somethings i forgot to mention in my last post, the aerial extension is connected to a wall socket which goes through a booster and up to the bedroom. There is still a tv signal without the booster power on.
what channels should i be changing the RF to?

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rob's 6 posts GB flag
rob's: mapR's Freeview map terrainR's terrain plot wavesR's frequency data R's Freeview Detailed Coverage

4:55 PM

DG: I realise you have directed the question at Brian, and whom I am sure will appreciate your comments, but if I could intrude into your posting to say that indications I have seen suggest that you might well be better pointing your aerial at the Nottingham multiplex transmitter as you are only 3 miles away from it.

The point about using Nottingham though is that as well as your aerial having to be turned around to face that direction (308 degrees from you) it also has to be turned to its vertical mounting position from its present state of being horizontal.

I really feel though that you would be best just replacing the aerial, especially when you have access to a ladder, I would recommend changing it to a log periodic type as these are capable of giving deceptively good performance in practically every type of location I have used them in, plus another bonus being that they have a low wind resistance and are not so likely to get moved by high winds. (Logs by the way are wideband)

As far as signal distribution is concerned, only use a powered splitter / booster to feed another room and "never" the "Y" shaped type which can kill the signal strength to both places.

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jb38's 81 posts GB flag

5:46 PM

rob: There is a list of frequencies in use in at your location here - Find out how to receive Freeview and Freeview HD | - independent free digital TV advice - pick one not in use.

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Briantist's 38,899 posts GB flag

7:25 PM

jb38: I don't mind the intrusion at all.

I would be very shocked to find that DG required much more than a contract aerial and passive splitters, come Wednesday 13th April 2011, to receive perfect reception from the Nottingham transmitter, as it is less than 3 miles away.

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Briantist's 38,899 posts GB flag

8:13 PM

Briantist: Yes! quite agree, as the increase in power to 400watts on all multiplexes after switchover should in theory blast in at the location mentioned.

I really meant to add to my reply (but forgot) that the aerial replacement should only be considered after a test has been carried on completion of repositioning the present one, but as DG was unaware as to the age etc of the present one thought it prudent to advise replacing it whilst having the chance of a ladder.

And of course without wishing to insult any one's intelligence, I likewise also meant to mention to DG not to forget and carry out a re-tune of his new freeview TV immediately after repositioning the aerial or Nottingham wont be picked up, as when one is involved in swinging aerials about its sometimes easy to forget this vital task.

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jb38's 81 posts GB flag
11:55 PM

thank you very much to both JB & Brian. Really helpful!

Please forgive my ignorance and advise me what a 'contract aerial' is?

If i do buy a new aerial, i have found this website here:

ease of reference, i find the above website useful. If you do know of anywhere in particular i should buy from, please do recommend. Otherwise i may just google the aerial i need, or pop to argos/b&q/screwfix.

Many thanks once again.

PS - the splitter is powered. oh, also, Nottingham is quite hilly in parts, would this affect which mast to aim for? (NG83HL)

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DG's 3 posts GB flag
Thursday, 3 February 2011

7:31 AM

DG: Sorry, yes, a "contract aerial" refers to a generic standard Yagi aerial (see Freeview reception - all about aerials | - independent free digital TV advice ) .

You can get better quality products from a professional store, compared to the high street stores, but for the basic type of aerial you need B&Q or Argos would be fine.

Your aerial should be mounted up as high as possible to ensure a line-of-sight to the transmitter. The Nottingham aerial is very tall to deal with the terrain in the area.

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Briantist's 38,899 posts GB flag

9:03 AM

DG: Well I do admit to being somewhat biased in favour of using logs at every opportunity, this basically because I have very seldom ever found that replacing one with a yagi etc type brought any significant gain over the previous log, and indeed over the many years (very!) of being involved with RF equipments (both Tx & Rx coupled to Dx TV having been a hobby) took great pleasure in demonstrating this fact to the many classic doubting Thomas types who live their lives besotted with manufacturers Db gain specs, and likewise feel that a massive piece of metalwork on their roofs just has to be better because a manufacturers spec says so. (Rant over!)

Anyway, ATV (Sheffield) on the link provided are a very good practical company and the DM log on their advert (@ £25.00) is an extremely good aerial and which I feel could not be improved on in the majority of locations it might used in if tested side by side with a much larger Yagi, but its really your choice "if" you decide to update after having tested your present aerial once its been repositioned.
(Of course aerial tests always having to be conducted with the same hour)

Briantist: I have to say that knowing the Nottinghamshire area there are as DG states some hilly areas hence why Waltham is bad in many places, and even although I did agree that after switch over DG's present set up would possibly be OK I did qualify this by saying "in theory", as even the few miles from the transmitter might well have some dastardly terrain obstruction.

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jb38's 81 posts GB flag

9:07 AM

jb38: I've checked the terrain map and it looks OK.

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Briantist's 38,899 posts GB flag
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