All posts by Nigel Johnson
Below are all of Nigel Johnson's postings, with the most recent are at the bottom of the page.
Since the beginning of July 2012, CH27 on Sandy Heath has produced weak and poor quality signals. especially during the day. All other mux channels are producing 10/10 signals.
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Further to my last comment on the poor quality of channel 27 from Sandy Heath.
I have noticed that all other Sandy Heath channels can be received without a problem, both with frequencies above and below channel 27. A closer examination of the reported signal strength and quality, indicates that even with a very strong signal, the quality is extremely poor, but only at certain times of the day.
I am beginning to wonder if the channel is subject to external interference.
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Sandy Heath (Central Bedfordshire, England) Full Freeview transTuesday 17 July 2012 10:52PM
Wisbech
Thank you for your suggestions. A mains network is certainly a possible source of the RF noise. As the problem is restricted to a single RF channel,I am reasonable confident that it is due to external interference rather than multi-path reception, which I assume would not be so frequency channel selective.
My receiver equipment reports a high signal strength on CH27, but intermittently very poor quality. Changing from a 10 down to a 1 or 2 every few minutes.
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NigelJ: The quality problems I have been experiencing with Sandy Heath channel 27 have for the moment spontaneously disappeared. I cannot say if this was due to the switch off of a local interference source, a corrected fault at the Sandy Heath transmitter or changes in atmospheric conditions reducing co-channel interference from some other transmitter.
Th fact that the problem was specific to CH27 and that the signal strength was consistently high, seems to rule out multi-path and fading due to atmospheric conditions, as these effect were unlikely to be restricted to only one MUX transmit frequency and would be associated with changes in signal strength.
I would be interested to know if there are any likely candidates as a source of co-channel interference, since this would mean that similar reductions in signal quality can be expected whenever the weather conditions match those of the past few days/weeks.
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Sandy Heath (Central Bedfordshire, England) Full Freeview transSaturday 21 July 2012 1:34AM
Wisbech
NigelJ: After a brief period of good reception of CH27 from Sandy Heath, I am back to the strong signal and unusable quality situation. I am now convinced that the problem is due to co-channel interference from other TV transmitters. In my case, most likely from Crystal Palace.
I can only conclude that during the system planning, an insufficient frequency reuse distance was defined to cope with adverse weather conditions.
If the co-channel interference source is in the direct line of the receiving aerial, there does not appear to much that can be done at the receiver to improve the Cr/Ci ratio.
Maybe a few more frequency channels should have been allocated to DTV and fewer to GSM4 LTE.
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Judging from the comments in recent postings, I am not the only one whose TV reception quality is being affected by weather related co-channel interference.
The clue to this type of interference is a strong signal associated with a very high error rate as reported by the signal quality display.
In my case such interference is at its worst just after sunrise and during the morning. As I reported in my earlier postings, the interference is mainly confined to CH27, which means I lose all the BBC channels.
Retuning when this happens, results in the TV finding the BBC mux from Belmont, which I assume is a normally weak signal, received from the side or back of the aerial.
At night signals from Sandy tends to recover and I see messages reporting "New Service Found".
It is interesting that for 30+ years I received TV signals from Sandy without any problem, except under extreme high pressure lift conditions. Now we have digital TV, the channel planning is so bad, Co-channel interference is common. Could it be that pressure from Government, keen to sell off RF spectrum, has resulted in too few channels being allocated to poor old Free-View?
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Sandy Heath (Central Bedfordshire, England) Full Freeview transSaturday 4 August 2012 1:36AM
Wisbech
I would be interested to know how many people are experiencing single RF channel interference. i.e. problem receiving all the logical channels on the same RF MUX frequency. I would like to establish if the reported problems are due to weather and time of day related co-channel interference. Should this be the case no amount of adjustment of the receiver or aerial is going to improve the situation.
Such interference is characterised by a high signal strength, which may change rapidly in value, and poor quality as measured by bit error rate.
Symptoms include picture freeze, pixelation and breaks in sound with associated pops and squeaks.
The tuning menu of most TV sets allow the user to check both the signal strength and quality on a scale of 0 to 10. This menu option also displays the frequency and/or RF channel number.
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It is not so much that the frequencies are dropping out because they are too weak, it's more a case of receiving several transmitters on the same frequency. You only need to look at the signal strength to understand that.
It is unfortunate that the best content, namely the BBC channels, is on the frequency with the highest level of interference. I would not miss some of the rubbish on the other MUX frequencies.
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Channel 27, which carries the BBC mux, on Sandy Heath is still unusable most of the time. All other Sandy Heath channels are received without a problem.
This is strange as the channels paid for by the TV licence are the only ones we cannot receive. I think it is time that BBC mux is switched to a better aerial on the Sandy Heath transmitter.
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Friday 11 May 2012 1:16AM
I cannot receive Sandy heath channel 48, all other channels received at 10/10 quality and signal strength. My postde is PE132EG