All posts by Alan_C
Below are all of Alan_C's postings, with the most recent are at the bottom of the page.
Chris.SE:
Many thanks for you comprehensive and helpful response.
In answer to your questions and comments:
Aerial is XB10K from ATV, mounted in the loft (using the cradle and a short pole down from the rafters).
The channels I lost were on the mux COM4 at channel 48, so actually not the highest frequency - I regret I don't know whether I also lost channel 55 (or indeed whether I even had it before the retune).
Prior to the PVR box filing I was using the signal strength indications on that, but I have found you are right that signal strength is available in a manual tune of the set.
Postcode: TA11 6SH.
I followed your recommended procedure today (Sat) now that the pressure has dropped (automatic retune with aerial disconnected, then reconnect (without splitter) and manual retune one channel at a time. Here are the strengths and qualities for each:
32 Q 100 L 65
34 Q 100 L 65
35 Q 100 L 55
48 Q 20 L 50
33 Q 100 L 60
36 Q 100 L 60
55 Q 0 L 0
30 Q 0 L 0
I viewed one channel briefly from each frequency channel (if you see what I mean) and they were all good (but of course I don't have any channels from 30 or 55).
So that's fantastic and thanks. Do you have any recommendations about 55 and 30?
Alan
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Chris:
Oh, and I meant to say that although the one channels (Drama) that I've watched so far on frequency channel 48 is watchable, there is intermittent pixellation. I'd be grateful for any suggestions about improving the signal for this channel, which came up with Quality 20% and Level (signal strength) 50% .
Thanks again,
Alan
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Chris.SE:
Chris:
Figures with amp connected (Commtel 4 channel amp/distribution device) in the loft, connected between the aerial lead and the cable running down to the wall plate, built in to the wall):
32 Q 60 L 100
34 Q 65 L 100
35 Q 0 L 100
48 Q 55 L 100
33 Q 30 L 100
36 Q 35 L 100
55 Q 0 L 95
30 Q 0 L 0
Note the increase in signal level across the band (including ch55); but also note the loss of quality across the band, with the exception of ch48 which benefits.
I know the Freeview map shows good coverage in my locality but the truth is there are many pockets in Somerton where people are slightly lower down and do not get good signals. Our installation situated on the plateau doesn't have unobstructed LOS to Mendip. It is also notable that about 50% of the properties around have two aerials - the other being directed to Stockland Hill. While this could be because they identify with SW rather than W region, it also apparent that we're about halfway between the two transmitters - and the direction to Stockland isn't far from -180 degree endfire on my aerial (I wonder what its reception pattern is like out of the back?). And I would add we get very poor FM radio even with a separate dedicated outdoor antenna, and no usable DAB. But that's off topic except that it does indicate we're not so well served by Mendip.
Thanks for the suggestions re. VCR, etc. We do have a VCR connected using SCART - I'd forgotten about the RF modulators in these things. Switching off the VCR and a DVD player, and removing an HDMI lead, made no difference to the signal / quality measures.
Interesting thought about standing waves in the cables. I've checked and swapped around all leads; also tried a long cable from the loft instead of the installed cable and wall plate. No changes seen.
The position in the loft is rather constrained, it needs to point through the gable end rather than the tiles because we have solar PV, and there aren't many places with enough headroom. The DC cable for the solar panels does run perpendicular to the aerial axis, close to the pole.
I'll wait for any further thoughts and comments before attempting to realign the aerial or move it sideways., as without any kind of analogue meter up there with me this is a bit of a trial and error activity. Initial alignment was just based on the required bearing!
Slight change of topic, but are we to expect Com7 to be switched off sometime in 2020?
Again, very grateful for your inputs (were you really typing at 4-5am?!!).
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Chris.SE:
Same report - the background map appears, centred on Pen Hill, but there are no coloured overlays in either standard or Pro mode. And no buttons.
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Chris.SE:
A quick but partial answer...
I like the idea of seeing what signal I can pick up from Stockland Hill using side lobes, without realigning the aerial - I'll do that at the weekend (don't want to get in the bad books of my wife). That'll also be the best time for me to try some rotation / repositioning of the aerial. And that's probably my best time for switching other things off. Like most people I guess, I have a few things which are "always on", like the wifi router. I don't think there's anything which has been put in fairly recently, though, except central heating (which has all wired thermostats, nothing radio-connected). My neighbour has been doing a lot of work in his house - I hope he hasn't installed anything operating on 690MHz!
Going back to the amplifier; when I tested with the amp disconnected it was moved away from the leads and fully powered down, and the aerial lead and the cable to the wallplate joined using a female-female back to back connector. As you've said, the figures show that the amp does provide gain ;-) which is probably not needed, and causes overloading of the tuner. But they do seem to suggest that the signal out of the aerial on Ch 48 is genuinely quite a bit lower than other channels; which isn't in line with the aerial gain curve?
Actually I don't have any other TVs anywhere - I installed the amp when my daughter came back to live for a while, and I put in an aerial point in another room for her - but since she left we haven't had a second TV. So I can carry on without the amp, but do you think it might be worth trying to put in some variable gain and find a sweet spot where Ch 48 is improved without overload on the others?
I'll do some more playing around next weekend.
Thanks for your continued assistance. Is this a hobby? I am impressed by your tolerance and politeness when responding to people with a wide range of attitudes!
Alan
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Chris.SE:
An interesting and initially frustrating day spent tweaking things and hoping to improve reception of channel 48 from my loft aerial.
I tried checking for signal from Stockland Hill and Wenvoe (without turning the aerial) and unamplified, I found nothing on any of the relevant channels (26+ etc.).
I tried isolating any possible source of interference, switching various things off - I think I found all the switch mode power supplies in the house. A search online suggested that the solar PV inverter in the loft (which is a switching design) was a potential problem, and I considered where I might add ferrites - but turning it off made no difference to the signal on Channel 48.
So I looked at the effects of rotating the aerial. I checked signal quality and strength as reported by the TV for Channel 48, and also Channel 33 as a reference. As well as rotation, I also moved the aerial a small amount along its axis (up to about 15cm) and sideways (about 5cm) but these didn't seem to make any difference. What did make a difference was when I lowered it a small amount (7cm) to allow enough room for it to turn. This resulted in noticeably lower signals on my reference channel.
I plotted all the results on a graph and it showed that the signal strength on Channel 33 had a maximum at 22 degrees; Channel 48 seemed to indicate a peak around 30 degrees but it never rose enough to get a decent signal quality; the maximum was about 25.
So I concluded that the aerial was already pointing in the best direction possible for that location, but then I thought again about the height effects and put it as high as possible while horizontal; then angled it up by 15 degrees. The results are as follows:
Channel Horiz. Quality Horiz. Strength +15deg Quality +15deg Strength
32 95 60 100 70
34 100 70 100 75
35 45 60 60 60
48 50 65 95 70
33 95 70 100 70
36 55 65 85 65
As you can see, angling it upwards has improved the signal across the board, presumably because it is capturing signal which is coming through the tiles rather than the gable wall.
So I now have satisfactory reception on Channel 48, as well as the others. It hasn't explained why that channel was so much more affected by the wall than the others.
In closing, very many thanks for your help and support, and I'm glad to say the outcome is looking good.
Alan
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Chris.SE:
I've obtained an attenuator (-20dB max) and done some more experiments. I connected aerial to amplifier to attenuator to TV and recorded signal quality and level at every whole turn of the attenuator knob - assumed to be a change of about 4dB per turn. Disappointingly, there was no attenuation setting at which the signal quality on Channels 35 and 48 was improved. I also tried it with the connections the other way around: antenna-attenuator-amplifier-TV; the results weren't any better.
I still don't understand why I'm getting poor reception on channels 35 and 48, yet 36 is excellent. I'm fairly sure that the LOS to Mendip transmitter grazes the top of a heavily-wooded hilltop. I think it looks as though I shall have to venture outside and try installing the aerial on the gable end wall, or failing that the chimney.
I suppose there's still one other thing I could try, and that's turning the antenna to point to Stockland Hill (you may remember I looked to see whether there was any signal on the Stockland channels but I did this without turning the aerial, just to see whether it had any sensitivity out of rear lobes!). Or I could knock a hole in the gable end!
By the way, I'm not clear about 55 - is it correct to say that this has now gone for good?
Alan
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Chris.SE:
Hi Chris, thanks for commenting back. I've only got a few notes to add at the moment; it seems I need another session of trial-and-error to see whether there's any way of getting an improvement. Unfortunately I don't think I have enough nerve to go up on the roof, so I'm stuck with trying the loft!
Thanks for clarifying the Ch55 story. It's academic to me at the moment, since I'm not getting anything on that channel, but I shall keep checking it and include it when I make comparisons!
I don't recall describing the aerial I bought as 48 element - it's an XB10K, "12 element" (10 directors, dipole and reflector), X-beam design (but I might have to go up and do a recount).
We've been getting worse reception / more pixellation the last couple of days, even though the weather is now dominated by a weak low pressure system. So I really will have to try changing the position. I guess the small changes I've tried aren't really enough in wavelength terms. Unfortunately it is very hard to find space for it to move - the reflector is right against the rafters as close to the apex as it'll go, so any attempt to move it means I have to position it lower.
I did wonder whether all cable on the market these days is 75 ohm impedance, and hence matched to the antenna (which has a balun)? If not, then maybe I've got a rogue length of 50 ohm or something!
I don't think all the trees have lost their leaves yet.
Best wishes,
Alan
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Wednesday 4 November 2020 9:15PM
A couple of unrelated comments. First the 5G clearance - changed the type of aerial needed to wideband. I could not find out anything about how to get assistance with aerial replacement, eligibility etc. - just a phone number. But as I work there was no way I would be able to hang on the phone for hours, go through the retune exercise multiple times etc. even though I'd already done that, so I bought one myself. Not happy that selling off the bandwidth has been at my expense.
Second, the channels on the mux which moved to the edge of the band have started to be pixellated and unwatchable in the last couple of weeks. Checked all my connections, etc. and found that some channels are better if I reduce the signal strength (removed aerial amp); even better when I added a splitter to introduce some attenuation. My PVR box strength and quality readouts were strength 85, quality 10 with amp in; with amp out 25,100. The mucking around involved switching the PVR off and on again several times and in the end it failed (Humax T1010 PSU fault) so now unable to check strength with splitter added. Does this make some sort of sense, does it suggest a distant transmitter interference? I suppose the amp could have been starting to fail and developed higher noise?
Third: Freeview swapped some channels on 4 Nov, forcing a retune. After the retune, all the channels on that mux have dropped off the EPG list. Presumably because they don't meet the threshold signal strength for the tuner and the previous information has been wiped?
So the main question: what's my best move to recover the missing channels? Should I try replacing the amp and retuning to get them back in the EPG list, then remove the amp again? Or try realigning the aerial (it is in the loft so has not been affected by storms, etc.). Or...?