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Inability to receive Local multiplex
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To help a friend with an old analogue TV this week, I dug out an old DTT receiver I bought from Lidl many years ago, a SilverCrest (re-badged Comag) SL-65. Even though ten years old, this worked almost perfectly, except that it doesn't see the Local multiplex, and hence London Live, POP, and QVC Extra. I wondered if it was because the multiplex is just QPSK and not QAM, but a friend who is a radio amateur, and happens to have a DVB-T modulator and the same Lidl receiver, set up the modulator with his local video sources, and found that the receiver worked fine.
Has anyone come across this before, and hence know why this receiver doesn't work? Maybe it's just an unusually low data-rate that it doesn't expect and can't lock on to?
Has anyone come across this before, and hence know why this receiver doesn't work? Maybe it's just an unusually low data-rate that it doesn't expect and can't lock on to?
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Check out your friend's prediction (detailed view) on http://www.digitaluk.co.uk/postcodechecker/ to see if they are meant to get it or not.
Of course this does assume your friend uses CP and not another transmitter (like Reigate or Hemel Hempstead).
Peter
I am however predicted to get zip on that frequency (and Tacolneston has a very directional aerial for it). Other TVs in the house are fed off the other port by an DA and none get the local mux.
So, yes, the tuner on the Panasonic is likely to be performing better than the cheap Lidl device's one!
PS My Panasonic shows a much lower signal level on the local than the 10/10 for all the other muxes, so using it's built in metering may give you some clue to the received levels?
What are the predicted (S)erved and (M)arginally-served numbers for your 100mx100m location square from digitaluk? I did a prediction for Horley, Surrey, recently that gave excellent numbers for all CP's muxes - except the Local where it predicted no reception (not even mentioned).
PS QPSK https://en.wikipedia.org/wiki/Phase-shift_keying#Quadrature_phase-shift_keying_.28QPSK.29 can also be expressed 4-QAM, as it uses the same principle as 16-QAM, 64-QAM and 256-QAM modulation... just labelled a different way. So it would be unlikely that the Lidl box cannot decode the simpler format.
Thanks again for your input.
TTFN, Peter
Ah, of course, OK. Yes, I was comparing like with like. Thanks - I wasn't aware of the actual figure.
Ha ha! Your original statement seemed so ludicrous it gave me pause, and I'm now so relieved that I was polite in my response! :-))
Now I suspect that the London local does not come from the main antennas on CP ... Checking the Ofcom spreadsheet confirms that:
LonTV is @129m agl and the main muxes are at 209m agl.
Coverage will be radically different and poorer as a result.
BTW The Panny's numbers are not dissimilar to mine for the Norwich mux.
What is required is line of sight ,plus a additional margins for terrain impedimemnts and although the usual increase in power is 10dB what is used on the main muxes on many sites is a margin of 20 dB .
So if a local mux is 10dB down at QPSK it will provide similar coverage and levels relative to the radio horizon to the main muxes.
Not yet Sue, he is busy re-decorating, but hopefully soon.
Yes, aerials are shown here.
http://tx.mb21.co.uk/gallery/gallerypage.php?txid=1&pageid=1719
Also don't forget that the service is transmitted as an SFN with Croydon too.
Crystal Palace coverage is shown in this document
http://d2a9983j4okwzn.cloudfront.net/downloads/ofcom-uk-local-tv-report-2011.pdf
That doesn't show what Croydon contributes, but mb21 shows the Tx array beams a signal south and east of the site,
http://tx.mb21.co.uk/gallery/gallerypage.php?txid=1259&pageid=2118
Excellent bit of engineering on these sites by the Arqiva engineers .
Importantly we still don't know what the digitaluk predicted coverage is... if it is not predicted to be reliably received at the location of Barney-Wol and/or his friend this is all just an academic exercise... albeit one that's keeping my old grey matter occupied for a change
4kw ERP as you know is the same as just under 40kw ERP at 64 QAM
Need to check using the cordinates of the TX and RX the path and refraction loss .
It then can be worked out the rooftop antenna gain needed .
Ham radio anoraks have the tools to do this as I am sure many on this forum do this also as most of my freinds in Arqiva are ham radio anoraks ,many who are very smart and make me feel like a dumb shmuck
Just looked at this thread starting with the OP and noticed something very odd which seems not to have been mentioned. I also have a SilverCrest (re-badged Comag) SL-65 which I bought from Lidl many years ago. I can assure you it is a FTA satellite receiver which at this moment is working well - connected to the satellite dish which came with it as a kit! So Barney-Wol is either confused over the model number or he is watching satellite channels. The latter would of course explain why he cannot receive the local DTT mux.
Edit: Looking at my notes from back in 2007 when I bought it, I see that Silvercrest also made an SL65 version for terrestrial digital reception (model with a T suffix) but this was intended for use in Germany, not UK. If this was also sold by Lidl in the UK it would definitely now be a non-standard UK DTT receiver.
Hello misar - definitely terrestrial! :-) The full model number is "DVB-T SL 65". Yes, Comag do now only seem to do satellite receivers, and confusingly use the same type number!
Dr.Oliver: I have looked at the coverage map, and I am JUST outside the purple zone for the main CP signal. I'm popping over to my friend's house on Friday which is on the other side of the hill, and has a much stronger feed from CP - will report back then.
I enlisted the aid of a friend who is a Radio Amateur, and has a UHF spectrum analyser. This showed the level of the Local Multiplex here in mid-Surrey was very low, only 8dB above the analyser noise-floor (unlike the main multiplexes which were 25-30). We then had a look at his aerial feed, from a much better location near Wimbledon, and saw levels about 20dB greater, with Local multiplex on channel 29 being a good clean signal (albeit 10-12dB lower than the main multiplexes). But still my old Lidl-sourced Comag receiver wouldn't decode the signal. It has a manual tuning feature, and telling it to look at channel 29, it showed a signal with 100% quality, but was unable to see any PIDs or Transport Stream :-(
What a shame Comag don't support it any more - I'd love to know what is going on.
8dB above the noise floor .
I am sure Arqiva have got it in hand and will sort it soon.
The engineers are very good and they will have it in hand as they do do tests around the coverage area.
If you have a standard rooftop antenna ,change it to a high gain wideband type and if the downlead is long fit a antenna pre amp .
This should lift the local TV multiplex sufficiently out of the noise floor so it should work.
Also some set top boxes have a lower noise tuner than others so improvements could be made if the model you are using has a poor noise level.
I am sure others on this forum have experiance on the best type of set top box.
Usually and I mean usually those with Philips (NXP) tuners work best ,or they did when I was doing such things .
You rather seem to be missing the point?, you keep making claims that 64QAM is 10dB 'better', yet the entire idea of local channels is to use the low power to restrict the coverage to a much smaller area (hence the name 'local').
This is borne out by 'real life', and Arqiva certainly won't be going round trying to figure out why coverage is much less than the main multiplexes, because that's how it's supposed to be.