Problems receiving BBC 2/3/4 and Ch4

[Nalaselig]

Hi,
I have already posted my problem as a reply to a post by Jonny_no2 beginning 19-01-09 but as a new member I wondered whether I should have sent it as a new post given his problem seem to have been solved so here goes again!
Our system has worked without any problems and any change in the set up for 3 years. Sine January we have been having the same problems receiving BBC 2/3/4 as Jonny_no2 but also TV4 and with a notable twist, there is a temporal relationship. BBC 2 is fine during essentially day light hours (~07.30-~19.30) and rapidly goes off (first increasing picture and sound breaking up progressing to message 'no satellite signal'). As BBC 3/4 do not start broadcasting until 19.00 we almost always get the 'no satellite signal' straight away. BBC is back to normal the following day but of course we cannot check 3/4.TV4 is bad for 24 hrs. whereas TV4 + 1 is usually fine during the same interval, which would tie in with the suggestion by Kenedin to Jonny_no2 of separating out channels that receive H rather than V-polarized signals. Our service engineer is completely stumped. He changed the LNB and reported a much stronger (65 > 90%) and better quality (~40 > ~80%) signal. This solved the TV4 problem but only when there no splitters in the line. If these were included, there was significant interference. It did not solve the BBC 2/3/4 problem. Shortening the cable from the LNB to the decoder from ~ 30 to ~5m with no splitters on the way gave full reception on all channels but there was still significant interference of both sound and picture quality with BBC 2/3/4. I have noted the comments about dish distortion being a problem and our problems did seem to coincide with the major snow we had this winter. Our dish is an 'environmentally friendly' transparent (plastic) type but I can see no obvious deformity. Are these known to be problematic over time?Any suggestions as to where we and our engineer should go next would be gratefully received.

[sdd]

can i be stupid here and ask why have you got splitters? and what for

[Nalaselig]

can i be stupid here and ask why have you got splitters? and what for

I should have been more precise. The satellite signal first goes through a 'coupler' (I live in France and that is the translation of the French word for it but it may not be the exact/correct English technical term) which 'couples' the signal with the one received from our terrestrial antennae so that the combined signal can be sent by a single coaxial line from our basement via a splitter feeding 2 single cables routed to the 2 rooms where the TV outlets are sited. We only use one at a time (one is virtually never used) and the combined signal goes through a ‘de-coupler’ which feeds 2 separate lines, one to the Sky digibox (Panasonic TU-DSB40) and the other to the TV’s terrestrial socket. I know it sounds complicated but should emphasize that it was working perfectly for 3 years before the problems started in January this year. There was no difference between the feeds in the 2 rooms and the problem we have now is also not improved by switching rooms. The only thing that helps is having a completely uninterrupted and significantly shortened line from the LNB. However, even then the improvement is only complete with CH4 and BBC 2/3/4 are not much better. I am beginning to think that it has to be the dish but before getting into the expense of replacing it I would like the benefit of the wisdom of others particularly because of this temporal relationship of the problem. Thanks for your help!

[dms05]

BBC3/4 use the same transponder as CBBC and CBeebies. The latter transmit until 20.00 CET. Can you receive CBBC and CBeebies during the day?

I must admit I'm not at all sure what your description of your set-up means. However for what it's worth the problems you are describing are also seen in the south of Spain BUT people have much bigger dishes (1.8-2.4m) and use the very best LNB's to overcome the problem. It's worth asking where you are in France and what size dish do you have? Again in southern Spain it's common knowledge that all receivers are not equal and some are very much better than others for this problem. Maybe it's the receiver that's nearing the end of its useful life.

I'm told that problem effects very low frequency Horizontally Polarised trnasponders (such as 10773H which carries BBC2 England CBBC/CBeebies and others) and one solution is to tune to another transponder carrying a regional version of BBC2 ie BBC2 Scotland (10803H). Most BBC1 regional variations on on Vertically polarised transponders and don't have the same problem. The same applies to ITV who use Vertical polarised transponders.

A good start would be a larger dish.

[Nalaselig]

BBC3/4 use the same transponder as CBBC and CBeebies. The latter transmit until 20.00 CET. Can you receive CBBC and CBeebies during the day?

I must admit I'm not at all sure what your description of your set-up means. However for what it's worth the problems you are describing are also seen in the south of Spain BUT people have much bigger dishes (1.8-2.4m) and use the very best LNB's to overcome the problem. It's worth asking where you are in France and what size dish do you have? Again in southern Spain it's common knowledge that all receivers are not equal and some are very much better than others for this problem. Maybe it's the receiver that's nearing the end of its useful life.

I'm told that problem effects very low frequency Horizontally Polarised trnasponders (such as 10773H which carries BBC2 England CBBC/CBeebies and others) and one solution is to tune to another transponder carrying a regional version of BBC2 ie BBC2 Scotland (10803H). Most BBC1 regional variations on on Vertically polarised transponders and don't have the same problem. The same applies to ITV who use Vertical polarised transponders.

A good start would be a larger dish.

Thanks for your comments and suggestions. I am sorry that the description of my system was not clear. To clarify, presently a single uninterrupted co axial line, ~30m in length, goes from the dish/LNB mounted on the wall of the second floor of our house to the basement where it goes through the circuitry I described in my first response. When I referred to getting significant but not complete resolution to the problems with a shorter (~6m) uninterrupted line, I did this by taking a line directly from the LNB through the window of a bedroom, close to the mounting, to the digibox/TV set up there temporarily. With regard to your other questions comments:
1. Other BBC channels/polarisation – As you and others have pointed out it is very clear that it is a polarisation-related problem. None of the BBC and all other channels (ITV/Sky) transmitting with vertical polarisation (BBC Transponders 48, 46 & 50) are affected but all except 3 BBC TV and 2 BBC radio channels with horizontal polarisation are affected (Transponder 45 / Freq. 10.77325 - BBC1 London, BBC2 England, BBC3, BBC4 & BBC1 NI; Transponder 47 / Freq. 10.80275 – BBC1 Scotland, BBC2 Scotland, BBC1 Wales, BBC2 Wales, BBC2 NI, BBC Radio 5 Live & BBC Radio 5 Live Sports Extra.). Interestingly, 3 BBC TV Channels (BBC Parliament, BBC News & BBC Alba) and all the remaining BBC radio channels apart from the 2 already mentioned, which transmit on Transponder 13 (Freq. 11.95350) and has horizontal polarisation, are fine. You will note that I have not included CBBC and CBeebies, which do transmit on Transponder 45. I am sure these would be affected but I cannot check as they broadcast during daylight hours and my problem only occurs after dusk and before dawn! BBC3/4 are the exact opposite!
2. Dish Size – I take your point about this. We live in a small sub-alpine village (alt. 550m) 10k south of Grenoble. Our dish diameter is 80cm. and our engineer assures that our LNB is the best available. I think, however, that I should re-emphasize that the system has worked perfectly well for 3 years until the problems started in January after significantly greater than usual snowfall. I am virtually convinced that we do have a dish ‘distortion’ or dish/LNB orientation problem. The temporal relationship is a bit bizarre but I am in the process of checking if we are dealing with voltage fluctuations, when the local community increases and decreases its power demands. as a cause for this. Either way, it appears to me that what I am dealing with is a marginal quality signal from horizontally polarised transmitters and that any other factor that compromises this, e.g. length of coaxial line, splitters or couplers in the circuit, voltage changes, etc., push it over the edge.
3. Receiver – By this I assume my digibox and or TV. I have the same problem using other TVs and when I take my digibox to a friend living in the same village who has the same setup, it works perfectly with his. Conversely, his digibox is if anything more susceptible to the problem than mine when substituted into my system

Apologies for the length of the response but may be my experience and testing will be useful to others as well as answering your very helpful contribution. Thanks again.

[dms05]

You seem to have established your digibox is OK if it works on another installation locally. The question is what length of cable do they use from LNB to digibox.

I'm still concerned about your splitter as you have to remember the satellite part not only carries the signal down to the receiver but also sends a voltage upto the LNB to switch polarity. This is either 13 or 18 volts and this switches the LNB from V to H. If the higher voltage is falling much below 18v then you will not see correct polarity switching and the LNB will default to V rather than switch to H. Also splitters will reduce the satellite signal, they always do.

You have established replacing the long cable with a shorter cable helps. I suggest your problems is partly due to the length of the cable. Normally an in-line amp isn't recommended for satellite (they don't boost a week signal) but if placed close to the LNB one may give you enough power to compensate for the long run and splitting. Remember any cable splitting will reduce the strength of the signal.

Having said all that the fact that the problem occured after heavy snow does support your comment about the dish deforming. This could effect the polarisation of the signal fed to the LNB. You should always adjust the LNB scew so thet it isn't vertical but is slightly turned in it's holder - close to the 0 deg meridian I set mine to be at 1 o'clock (ie turned slightly clockwise so the centre line points to the 1 position on a clock).

I must repeat the experience of those in S Spain. They have weak and variable signal depending upon the time of day - they overcome this with larger dishes and VERY expensive LNB's not the usual LNB fitted to a small 80cm dish.

I'd personally start by stripping out the splitter/coupler as that will always degrade the signal. Then I'd replace the dish.

Good luck.

[Woodster]

I think he has a terr/sat diplexer, not a splitter, and another one to seperate the sigs at the stb. These components will ony give a 2dB through loss on satellite. I would agree that the dish size or distortion is the most likely cause, it may even be the cable or connectors, but there could be some other external source causing the loss of channels. Taxi company's, ham radio, that kind of thing.

[Nalaselig]

I think he has a terr/sat diplexer, not a splitter, and another one to seperate the sigs at the stb. These components will ony give a 2dB through loss on satellite. I would agree that the dish size or distortion is the most likely cause, it may even be the cable or connectors, but there could be some other external source causing the loss of channels. Taxi company's, ham radio, that kind of thing.

Thanks guys,
Woodster is correct, it is a terr/sat diplexer, which literally translated from the French term is a coupler, i.e. it couples the signal received from the LNB with that received from our terrestrial antennae. However, there is also a splitter in the circuit enabling the combined signals to be split to 2 alternative locations for plugging in our TV & digibox. When we do this Woodster is also correct that we use a second terr/sat diplexer or ‘de-coupler’ to separate out the 2 signals again. However, having said all that, cutting out either the terr/sat diplexers or the splitter or both improves but does NOT cure the problem. As far as the length of the line is concerned, my friend’s is probably longer than ours! I am checking for voltage fluctuations in our power supply at the moment and preliminary observations suggest that this may indeed be an issue but I doubt that this is a recent phenomenon whereas my problems with reception are. There are no ham radio operators in the vicinity that I know of and our village is too small to support a taxi service! I will certainly try the suggestion of rotating the LNB but I strongly suspect that I will be investing in a new dish. Thanks again for your input. I shall keep you posted.