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All posts by Tony Whyman

Below are all of Tony Whyman's postings, with the most recent are at the bottom of the page.


I have a problem with yesterday's COM7 retune at Rowridge. COM7 disappeared from channel 31 and has failed to re-appear on channel 55. The problem is common to two different TVs. The aerial was replaced in Jan 2018 with a Labgear LHG10T, so I doubt whether this is an aerial problem and both TVs report channel 56 (COM8) with 100% Signal Quality - all the other multiplexes are fine with a similar signal quality and all with good to 100% power levels. Even the LSO on channel 37 comes in at 100% signal quality.

It seems as if channel 55 is being filtered out somewhere - although I am wondering if as we are only Hannington/Rowridge boundary in SO24, the two signals may be cancelling each other out. Although on our side of the hill, Hannington is usually much the weaker signal.

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GB

I now tried adding a masthead amp and even at various settings up to the max 26dB, there is nothing on channel 55.

Is there anyone out there who is getting COM7 from Rowridge?

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colin1951uk:
Well, if you are getting 45% at Eastleigh, I'm not so surprised that by Alresford it gets down to 0%. However, there is something seriously amiss with COM7 (ch 55) from Rowridge. Com8 (ch 56) comes in here at a signal strength of 90% with a 0 BER and all the other multiplexes are up around the 98% mark. Before the switch, Com7 (ch 31)was always the worst at 74%, but never so bad as to be unavailable.

Pre-switchover, the signal strength of COM7 was meant to 24.4K with Com8 down at 18K. To get this bad, they must have reduced the signal strength down to sweet FA. Even before digital switchover we got all the multiplexes at often low power levels.

Maybe the transmitter output mask has been configured wrongly. That seems to be the only way COM7 could have got so bad compared with Com8.

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Well this is interesting. Looks like the power level has been increased on ch55 (COM7) from Rowridge. As I posted earlier, COM7 disappeared here in SO24 when it moved to ch55. This was no aerial problem as I had a new group T aerial and ch56 (com8) comes in at 90% signal strength, while ch55 was showing zero.

Checking ch55 again yesterday evening and lo and behold it's there with a signal strength of 86/90% and signal quality of ~70%. Indeed, better than the old ch31 and very similar to the COM8 figure. I have changed nothing here, so the improvement must be upstream.

If someone was listening and upped the power level or changed the directional mask, then a big thank you.

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MikeP:
I understand your point, but I doubt whether this is the case here. I suspect that the definition of "Signal Strength" varies between different TVs - 100% of what? BER is probably a better comparative measure.

On PSB1, 2 and 3, my TV reports a signal strength of ~98% but 0 BER. So I interpret that as a good quality signal and no more. I don't have a masthead amp and we are in a fringe area and so I doubt whether 98% signal strength means anything more than that. If I was seeing the same signal strength but a BER >0 then over-modulation may be taking place - but I have never seen that.

COM7 and COM8 are showing a BER of typically ~500 but with the high pressure this has gone up to ~1500 and last night both went over the 2K mark (and fell off the digital cliff). So all is not wonderful. Ch31 and Ch37 were more stable than this and I suspect that the higher frequency is to blame - and possibly Hannington.

The main point of my original post is that suddenly COM7 was there when it was not last week. Now it is showing "signal strength" and BER similar to COM8. So what changed?


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MikeP:
Sorry, I'm not convinced.

I have a 6db attenuator which I have put inline with the TV aerial in order to test out your point. That is enough to drop the reported signal strength on channel 21 (PSB3) from 96% to 92% (but still a reported 0 BER). On the other hand, COM7 (ch55) and COM8 (ch56) are behaving themselves this afternoon and without the attenuator are reporting 90% signal strength with a BER of around 500.

As soon as I put in the attenuator, channels 55 and 56 are completely trashed. Signal strength zero and 2000 BER - and this while PSB3 reports only a 4% drop.

I can only conclude that the reporting of 96% on a high power mux is not the same as 90% on a low power mux and reducing the signal strength is not going to help matters. Perhaps swinging the aerial round to point to Hannington might improve matters - but then there are trees and a hill in the way.

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