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TV on different aerial causing interference?
"Ian Jackson" wrote in message
... In message , Woody writes "Al" wrote in message . 1.4... Strange one this ... Parents got a new TV for their kitchen recently (Samsung LE19R8) and sure enough their indoor aerial wasn't good enough as expected. So, they had another aerial installed and a seperate downlead to the kitchen. The aerials are both on the same chimney mast and the downleads run along side each other until they reach a lower level and go their seperate ways. (No, I don't know why they didn't get a booster and a splitter). 2 TVs in the front room, one old analogue and an IDTV fed from one aerial with a passive splitter (yes, I know). There's a VCR in there somewhere also. Kitchen TV on it's own aerial. Everything works fine ... Until the kitchen TV is put on ITV on digital, and then Channel 4 in the front room is unwatchable on analogue - Snowy vertical rolling. Fine on digital on the IDTV. Change channel on the kitchen TV or go to ITV via analogue and everything is fine. If I swap the kitchen TV and the analogue TV over there is no problem. It sort of implies that there's something weird happening when the 2 digital TVs are on different aerials. I wanted to remove the VCR and the splitter and try some more combinations but the parents are paranoid that it won't work again (nice to be trusted!). I can't believe that the kitchen TV is putting interference up the aerial lead and that it's cross coupling with the other aerial. The coax looks to be good quality foil shielded and both aerials seem to be giving good signal strength. I'm baffled :( Al. Likely that the local oscillator (or possibly the computer clock) is getting back up the aerial and coupling across to the analogue aerial or downlead. If you swap the TVs you said yourself that there is a VCR in there and if the TV is the last item in the chain then there is no path back through the VCR to the aerial - many VCR local outputs are amplified. As others have said relocate one of the aerials, or if you have enough signal fit an attenuator in the DTTV cable at the TV end. You will then maximise the interferring losses and possibly reduce it enough to remove the Ch4 problem. For analogue channels, the 'N+5' and 'N=5' allocations were strictly been abandoned? If so, I can see some muxes getting clobbered by an analogue TV tuned to a channel five channels down. But maybe they have still avoided this relationship? For example, I see that, with the Crystal Palace allocation, no digital mux is N+5 wrt an analogue channel. However, there are three allocations where there is something N+5 wrt a digital mux (25 on 30 analogue, 28 on 30 analogue, and 29 wrt 34 digital). But do the digital STBs and TVs have the same local oscillator and IF as analogue TVs - or do they use something different? If they are the same, do the digital tuners simply have much less radiation of the local oscillator? -- Ian Emley (which I use) is analogue 37, 41, 44, 47, 51 and digital is 40, 43, 46, 49, 50, 52. My simple maths suggests that the N+5/N=5 rule is truly no more. -- Woody harrogate three at ntlworld dot com |
TV on different aerial causing interference?
In message , Woody
writes "Ian Jackson" wrote in message ... In message , Woody writes "Al" wrote in message .1.4... Strange one this ... Parents got a new TV for their kitchen recently (Samsung LE19R8) and sure enough their indoor aerial wasn't good enough as expected. So, they had another aerial installed and a seperate downlead to the kitchen. The aerials are both on the same chimney mast and the downleads run along side each other until they reach a lower level and go their seperate ways. (No, I don't know why they didn't get a booster and a splitter). 2 TVs in the front room, one old analogue and an IDTV fed from one aerial with a passive splitter (yes, I know). There's a VCR in there somewhere also. Kitchen TV on it's own aerial. Everything works fine ... Until the kitchen TV is put on ITV on digital, and then Channel 4 in the front room is unwatchable on analogue - Snowy vertical rolling. Fine on digital on the IDTV. Change channel on the kitchen TV or go to ITV via analogue and everything is fine. If I swap the kitchen TV and the analogue TV over there is no problem. It sort of implies that there's something weird happening when the 2 digital TVs are on different aerials. I wanted to remove the VCR and the splitter and try some more combinations but the parents are paranoid that it won't work again (nice to be trusted!). I can't believe that the kitchen TV is putting interference up the aerial lead and that it's cross coupling with the other aerial. The coax looks to be good quality foil shielded and both aerials seem to be giving good signal strength. I'm baffled :( Al. Likely that the local oscillator (or possibly the computer clock) is getting back up the aerial and coupling across to the analogue aerial or downlead. If you swap the TVs you said yourself that there is a VCR in there and if the TV is the last item in the chain then there is no path back through the VCR to the aerial - many VCR local outputs are amplified. As others have said relocate one of the aerials, or if you have enough signal fit an attenuator in the DTTV cable at the TV end. You will then maximise the interferring losses and possibly reduce it enough to remove the Ch4 problem. For analogue channels, the 'N+5' and 'N=5' allocations were strictly been abandoned? If so, I can see some muxes getting clobbered by an analogue TV tuned to a channel five channels down. But maybe they have still avoided this relationship? For example, I see that, with the Crystal Palace allocation, no digital mux is N+5 wrt an analogue channel. However, there are three allocations where there is something N+5 wrt a digital mux (25 on 30 analogue, 28 on 30 analogue, and 29 wrt 34 digital). But do the digital STBs and TVs have the same local oscillator and IF as analogue TVs - or do they use something different? If they are the same, do the digital tuners simply have much less radiation of the local oscillator? Once again, correcting my mistake... Should be 28 on 33 analogue. Emley (which I use) is analogue 37, 41, 44, 47, 51 and digital is 40, 43, 46, 49, 50, 52. My simple maths suggests that the N+5/N=5 rule is truly no more. You're dead right. A41 hits D46, and A47 hits D52. I'm surprised that this does not cause the occasional problem. D46 also hits A51 but, assuming that digital tuners are engineered to a much higher standard, and don't radiate much local oscillator, that might be OK. Maybe the whole N+5/N-5 was a complete myth! -- Ian |
TV on different aerial causing interference?
charles wrote:
In article , Al wrote: Strange one this ... [Snip] I can't believe that the kitchen TV is putting interference up the aerial lead and that it's cross coupling with the other aerial. The coax looks to be good quality foil shielded and both aerials seem to be giving good signal strength. not knowing where you live, and therefore which transmitter you receive, make a proper diagnosis difficult. I would think that your kitchen tv is indeed sending a signal back up the aerial lead and that is getting across into the other aerial. This does happen, or certainly used to in the analogue days. The solution is to move the two aerials further apart. What would be a recommended minimum separation? When some houses near my home were being re-roofed, the contractors re-fitted aerials up to 6 to a mast, barely a foot apart. They were all pointing at an analogue relay within line of sight (and with no Five), so there might have been less of a problem. The greater problem was the masts all bent over in the first gale, though the signal was probably still OK. |
TV on different aerial causing interference?
A similar query was posed some years ago and the answer then was that
when too many TV aerials are placed closed to each other they interfere causing them, and I quote, "to detune each other". Move the aerials apart, or remove one aerial and have both TVs fed off the same aerial. John |
TV on different aerial causing interference?
Ian Jackson wrote:
Emley (which I use) is analogue 37, 41, 44, 47, 51 and digital is 40, 43, 46, 49, 50, 52. My simple maths suggests that the N+5/N=5 rule is truly no more. You're dead right. A41 hits D46, and A47 hits D52. I'm surprised that this does not cause the occasional problem. D46 also hits A51 but, assuming that digital tuners are engineered to a much higher standard, and don't radiate much local oscillator, that might be OK. Maybe the whole N+5/N-5 was a complete myth! No it's not a myth, but there are two things to remember. Firstly the image rejection performance of modern tuners is very good, secondly the whole rationale behind fitting DTT into the UHF band alongside the analogue channels was to make use of what were previously 'Taboo' channels. i.e. N+/-9, N=/-5, and indeed N+/-1. |
TV on different aerial causing interference?
"Woody" wrote in message ... "Ian Jackson" wrote in message Emley (which I use) is analogue 37, 41, 44, 47, 51 and digital is 40, 43, 46, 49, 50, 52. My simple maths suggests that the N+5/N=5 rule is truly no more. The n+9 rule hasn't been obeyed for ten years. Bilsdale analogue includes 26 and 35. Bill |
TV on different aerial causing interference?
"Ian Jackson" wrote in message ... You're dead right. A41 hits D46, and A47 hits D52. I'm surprised that this does not cause the occasional problem. D46 also hits A51 but, assuming that digital tuners are engineered to a much higher standard, and don't radiate much local oscillator, that might be OK. Maybe the whole N+5/N-5 was a complete myth! Some of these very cheap flatscreen supermarket sets have brought it back! I always get the impression that the manufacturers know how to make a screen, but have no idea about adding the RF bits! T'other day the customer had a 19" set which had cost £89.99. The performance of the analogue tuner was truly dreadful. Incidentally, the customer thought (asumed?) that the set was 'all ready for digital' but it didn't have a digital tuner. I added a DTT set top box (because the picture on analogue was so bad) and bugger me the picture via the (composite) scart had a pattern of fine lines (looked like internally generated interference) and the RGB scart was very dull and couldn't be adjusted. Bill |
TV on different aerial causing interference?
"Jim" wrote in message net... charles wrote: When some houses near my home were being re-roofed, the contractors re-fitted aerials up to 6 to a mast, barely a foot apart. Like this? http://www.wrightsaerials.tv/roguesg.../061.html#img1 Bill |
TV on different aerial causing interference?
wrote in message ... A similar query was posed some years ago and the answer then was that when too many TV aerials are placed closed to each other they interfere causing them, and I quote, "to detune each other". Move the aerials apart, or remove one aerial and have both TVs fed off the same aerial. It won't help if the problem is IF going up the cable from one set. Bill |
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