Two frequency interference
Brian Butterworth published on UK Free TV There are several different type of interference that causes problems. This page deals with the situation where:
- Freeview reception is perfect or near-perfect most of the time
- Several channels are missing, and they are all on the just two 'multiplexes'
Transmission mode problem
If you are unable to receive the channels on BOTH multiplex 2 and multiplex A, this will be down to the transmission mode. See Freeview modes.This is a particular problem for people using Loft aerials and Indoor aerials .
Non-wideband aerial in some areas
In some places you will need a wideband aerial to receive all the Freeview multiplexes. To find out if you need an aerial upgrade, see My Freeview reception.Help with Freeview, aerials?
Monday, 3 January 2011
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Mark7:51 PM
Woodford Green
Three of my neighbours and I have been suffering in silence over the past 8 months (approx) with the reception of MUX 2 & A channels, all assuming the problem was within our individual houses / setup. I can see from this site that the problem appears to be 'two frequency interference' but cannot see what is recommended to fix the problem.
Both a neighbour and I have consulted professional arial installers and both have indicated that newly erected buildings in the area are likely to blame and suggested the only solution is to switch to using satellite or cable feeds. Although I am not disregarding this advice entirely I am sceptical that this interference would result in the loss of MUX 2 & A channels only. Also worth noting is that these new buildings are about 6 floors each and roughly quarter of a mile away so I'd be surprised if these were in direct line of our transmitter at Crystal Palace.
My testing so far has included using two different televisions, both with built in freeview, directly to arial sockets and via PVR, from different rooms. My arial is 4 years old and roof mounted with a Triax booster/splitter in the loft space. As stated at the outset I am not the only one who has encountered this issue so doubt it is a setup issue but am happy to be enlightened!
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Mark's: mapM's Freeview map terrainM's terrain plot wavesM's frequency data M's Freeview Detailed Coverage
Tuesday, 4 January 2011
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Tony Conquest12:16 PM
Sudbury
My sky HD box is stopping me receiving anything on Multiplex 2, I've tried various RF out put channels on my sky box but other than by-passing the sky box I am unable to receive Multiplex 2.
If I by-pass the Sky box the digital signal is great on all channels (Multiplex's).
I am using the Sudbury Suffolk signal as I live only 7 miles from the transmitter
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Tony's: mapT's Freeview map terrainT's terrain plot wavesT's frequency data T's Freeview Detailed Coverage
Thursday, 6 January 2011
Tony Conquest: You are probably just degrading your signal enough to block multiplex 2.
I would just bypass your Sky box until the high power signals come online on 20th July 2011.
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Mark: You are not predicted to receive Multiplex 2 with anything like a stable service until switchover in 2012, I am sorry to say.
I wouldn't waste any additional money trying aerial things to deal with this, as you will be spending good money after bad.
I would strongly suggest you add a Freesat receiver and dish to your system - this will get you all the missing channels. All about Freesat | ukfree.tv - independent free digital TV advice has the details.
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Sunday, 8 May 2011
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Rudy Walker8:26 PM
Two frequency interference
What to do when Freeview reception is perfect, but several channels are missing, and they are all on just the two 'multiplexes'.
So... what is the solution??????? (53.0916,-1.2495)
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Mike Dimmick10:32 PM
Nottingham
Rudy Walker: the page really talks more about why it might be two frequencies that are a problem, and not really anything to fix it.
The mode used by Mux 2 and A before switchover requires higher signal-to-noise ratio than the other four multiplexes, which means that if your reception is deteriorating you would tend to lose these first. After switchover, all five SD multiplexes use the same mode.
The location you've provided is near NG17 8RH. That postcode appears to be problematic: Digital UK's predictor does not offer a six-multiplex prediction from any transmitter, at the moment. This might be a reduction of coverage due to interference from other transmitters having switched over, but it's more likely that you've never really been in reliable coverage and the current conditions mean it's not working right now.
You're between three main transmitters: Waltham, Sutton Coldfield and Emley Moor. Waltham provides the East Midlands service, but it's less powerful and there's a terrain problem which means the probability of finding reliable reception is lower than from the other two. There will also be a channel clash between the ArqB multiplex from Waltham and the D3&4 service from the Bolehill relay - both using C57 - which would likely mean you couldn't get reliable service on this multiplex.
You should get best results from Sutton Coldfield. Emley Moor is a slightly poorer alternative but there's not a lot in it.
The Nottingham transmitter has already switched over, but terrain blocks line-of-sight and the radiation pattern is concentrated to the east and south.
If the aerial currently points to Waltham, you would have needed to retune on 30 March and 13 April, as Mux 2 and A have changed frequencies for the last six months before switchover. Make sure you do a full device reset - some boxes will ignore a new location for channels that they already have stored. See how well it performs after switchover, and if it's not reliable enough, consider changing to one of the other transmitters.
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Mike's: mapM's Freeview map terrainM's terrain plot wavesM's frequency data M's Freeview Detailed Coverage
Tuesday, 10 May 2011
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Rudy Walker12:57 AM
Rudy Walker: the page really talks more about why it might be two frequencies that are a problem, and not really anything to fix it...
Mike Dimmick
Thank you for your prompt response.
The mode: Yes understood
The location: Post code is NG17 8RJ... a brand new street, and am not altogether confident in the predictor! The coverage here has since moving in, in January, been perfect (from Waltham) on all DTV and analogue channels, until 30 March when I re-tuned as advised and lost Mux A and again on 13 April where I lost Mux 2! I can't see a clash on C57 as it is currently not used, well not until August anyway.
The Nottingham transmitter: Would it be beneficial to switch to this transmitter, bearing in mind I am only 7.3km away from it, albeit slightly NW?
The Twist: I performed another complete re-tune this evening (as advised by the note appearing on my screen)... and picked up Mux A (C29) with a 'good' signal quality & a 'very strong' signal level (but still no Mux 2(C31)... signal quality 'poor' & signal level '0-50% fluctuating'
Conclusion: It seems that without doing very much myself, half the problem has solved itself!!! Are they still working on the "problem"?
Once again many thanks for your input (53.0916,-1.2495)
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Rudy Walker1:24 AM
Mike Dimmick
Does this mean I now have "single frequency interference"
I am not sure how to proceed here as;
Local analogue interference: I don't have Sky, Virgin etc, just a DTV with built-in Freeview. No VCR or PVR, but I do have an X-Box games console, however this is turned off and unplugged.
Non-wideband aerial: I have a brand new wideband aerial, however it's use seems somewhat redundant as I understand it Mux 2 is not an 'out of group' multiplex on Waltham transmitter.
Any suggestions or should I just wait it out for all engineering works to be completed
Best regards (53.0916,-1.2495)
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Saturday, 14 May 2011
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Rudy Walker9:19 PM
Nope spoke too soon... lost Mux A (C29), only had it for a day!!! (53.0916,-1.2495)
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Sunday, 15 May 2011
Rudy Walker: I note that Bisdale also uses C29, it is possible that you are getting periodic interference from there.
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