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TV on different aerial causing interference?
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. |
TV on different aerial causing interference?
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. -- From KT24 - in "Leafy Surrey" Using a RISC OS computer running v5.11 |
TV on different aerial causing interference?
On Feb 23, 11:52 am, Al wrote:
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. Well, I can. From what you're describing, it sounds like the second aerial has been mounted too close to the first one. Just as Charles has said. Cheers. |
TV on different aerial causing interference?
My mate was tuning his analogue TV some years ago, and as it was scanning
the stations it suddenly stopped and he could see someone typing in a Basic program on his TV screen! A bit snowy and wobbly, but perfectly clear enough to read. This was in the days when people used their TV as a computer monitor. Presumably a close neighbour was playing with his Spectrum or whatever, and something was leaking enough for my mate's aerial to pick it up, and his auto-tuning to lock on to it. SteveT |
TV on different aerial causing interference?
"Al" wrote in message
. 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. -- Woody harrogate three at ntlworld dot com |
TV on different aerial causing interference?
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. Aha! That's one thing that I forgot. My Dad said something about the VCR output being boosted, which made me suspicious and wanting to take it out of the equation. As others have said relocate one of the aerials I'm not sure how easy that would be. Next time I visit I'll take a look. Not sure how far away they should be spaced. This isn't a combined array, so the half wavelength rule is (probably) irrelevant. I'm still struggling to see how/why a TV would be pushing a signal *up* the feed, but my hunch is that the tuner impedance changes enough to effectively cause a load on the other aerial. fit an attenuator in the DTTV cable at the TV end. Good idea. Thanks to all that have posted - I'm much now somewhat wiser :) Al. |
TV on different aerial causing interference?
In message , Woody
writes "Al" wrote in message .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 |
TV on different aerial causing interference?
In message , Ian Jackson
writes 28 on 30 analogue, Oops! Should be 28 on 33 analogue. -- Ian |
TV on different aerial causing interference?
Al wrote:
I'm not sure how easy that would be. Next time I visit I'll take a look. Not sure how far away they should be spaced. This isn't a combined array, so the half wavelength rule is (probably) irrelevant. What half-wavelength rule would that be? IME multiple aerial installations like yours invariably have the aerials mounted too close. I'm still struggling to see how/why a TV would be pushing a signal *up* the feed, There's always some LO leakage, hence the N±5 rule for analogue. The problem here though doesn't sound like LO interference; that would show as herring-bone patterning and what you've described seems more like a noise-like signal coming out of the kitchen TV's tuner - an intermodulation product involving the LO and one or more DTT signals, perhaps? Are you in a high-signal strength area? As Charles said, the most important piece of information needed is the name of the transmitter site that the aerials are looking at. Things you could try: (i) attenuate the input to the kitchen TV: a 6 dB pad could make a big difference - it will reduce the level of any intermod products in the tuner's front-end as well as improving the effective isolation between the aerials; (ii) buffer the i/p to the kitchen TV using a set-back booster type amplifier, followed by a 10 dB pad (you don't need the gain, but the buffering effect of the amplifier should certainly help). -- Andy |
TV on different aerial causing interference?
"Al" wrote in message . 4... fit an attenuator in the DTTV cable at the TV end. When this sort of problem occurs, a small one-in one-out amplifier, followed by an attenuator if necessary, prevents anything getting back up the downlead. Bill |
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 |
TV on different aerial causing interference?
In message , Bill Wright
writes "Jim" wrote in message onet... 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 I bet the aerial on the wall is for the warden/manager. -- Ian |
TV on different aerial causing interference?
In article , Bill Wright
wrote: "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. by the time C5 appeared sets had got better. My aerial set up had CP on 33 & Hannington on 42. My original colour set, Thorn 3000 series (ISTR) , didn't like it - later sets didn't mind. But I had to remove the Hannington feed when Digiatl TV came along. Can't remember why - it might have been N+9 again. That was with the old ITV digital box. -- From KT24 - in "Leafy Surrey" Using a RISC OS computer running v5.11 |
TV on different aerial causing interference?
charles wrote:
In article , Bill Wright The n+9 rule hasn't been obeyed for ten years. Bilsdale analogue includes 26 and 35. by the time C5 appeared sets had got better. My aerial set up had CP on 33 & Hannington on 42. My original colour set, Thorn 3000 series (ISTR) , didn't like it - later sets didn't mind. But I had to remove the Hannington feed when Digiatl TV came along. Can't remember why - it might have been N+9 again. That was with the old ITV digital box. It would have been because from Nov 1998 until Aug 2000, both CP and Hannington each used E29 for one of the muxes. Hannington ditched the used of E29 in 2000, but Oxford now uses it. |
TV on different aerial causing interference?
In article , Mark Carver
wrote: charles wrote: In article , Bill Wright The n+9 rule hasn't been obeyed for ten years. Bilsdale analogue includes 26 and 35. by the time C5 appeared sets had got better. My aerial set up had CP on 33 & Hannington on 42. My original colour set, Thorn 3000 series (ISTR) , didn't like it - later sets didn't mind. But I had to remove the Hannington feed when Digiatl TV came along. Can't remember why - it might have been N+9 again. That was with the old ITV digital box. It would have been because from Nov 1998 until Aug 2000, both CP and Hannington each used E29 for one of the muxes. That makes very good sense - except that Hannington doesn't radiate digital in my direction. But perhas there was enouh to muck up cpCP. Hannington ditched the used of E29 in 2000, but Oxford now uses it. -- From KT24 - in "Leafy Surrey" Using a RISC OS computer running v5.11 |
TV on different aerial causing interference?
charles wrote:
In article , Mark Carver It would have been because from Nov 1998 until Aug 2000, both CP and Hannington each used E29 for one of the muxes. That makes very good sense - except that Hannington doesn't radiate digital in my direction. But perhas there was enouh to muck up cpCP. I've got a feeling the E29 mux had a different radiation pattern, to the present DTT transmissions. It had to be restricted towards the NW of Hannington, because of Cirencester analogue, so there might have been more radiation eastwards ? -- Mark Please replace invalid and invalid with gmx and net to reply. http://www.paras.org.uk/ |
TV on different aerial causing interference?
In article ,
Mark Carver wrote: charles wrote: In article , Mark Carver It would have been because from Nov 1998 until Aug 2000, both CP and Hannington each used E29 for one of the muxes. That makes very good sense - except that Hannington doesn't radiate digital in my direction. But perhas there was enouh to muck up cpCP. I've got a feeling the E29 mux had a different radiation pattern, to the present DTT transmissions. It had to be restricted towards the NW of Hannington, because of Cirencester analogue, so there might have been more radiation eastwards ? at least Circenceter was VP -- From KT24 - in "Leafy Surrey" Using a RISC OS computer running v5.11 |
TV on different aerial causing interference?
charles wrote:
In article , Mark Carver wrote: charles wrote: In article , Mark Carver It would have been because from Nov 1998 until Aug 2000, both CP and Hannington each used E29 for one of the muxes. That makes very good sense - except that Hannington doesn't radiate digital in my direction. But perhas there was enouh to muck up cpCP. I've got a feeling the E29 mux had a different radiation pattern, to the present DTT transmissions. It had to be restricted towards the NW of Hannington, because of Cirencester analogue, so there might have been more radiation eastwards ? at least Circenceter was VP So is Guildford ;-) -- Mark Please replace invalid and invalid with gmx and net to reply. www.paras.org.uk |
TV on different aerial causing interference?
Bill Wright wrote:
"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 The aerials were all mounted vertically on a single mast, all with vertical polarisation. In your example, the aerials are mounted on horizontal spars and the vertical separation is greater. Which would be worse for overlapping fields? |
TV on different aerial causing interference?
"Jim" wrote in message net... Bill Wright wrote: "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 The aerials were all mounted vertically on a single mast, all with vertical polarisation. In your example, the aerials are mounted on horizontal spars and the vertical separation is greater. Which would be worse for overlapping fields? It's hard to say really, but in general I would have thought that if the dipoles were broadside on there would be more chance of signal passing from one to the other. Bill |
TV on different aerial causing interference?
On Feb 25, 8:40*pm, "Bill Wright"
wrote: "Jim" wrote in message net... Bill Wright wrote: "Jim" wrote in message ronet... 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 The aerials were all mounted vertically on a single mast, all with vertical polarisation. *In your example, the aerials are mounted on horizontal spars and the vertical separation is greater. *Which would be worse for overlapping fields? It's hard to say really, but in general I would have thought that if the dipoles were broadside on there would be more chance of signal passing from one to the other. Bill- Hide quoted text - - Show quoted text - Could be coupling between the two sections of coax running alongside each other, this is likely to be comparable to the coupling between the two antennas. I believe many modern digital tuners use a zero IF technique with the recovered I & Q signals being applied directly to the demodulator chipset. So the avoidance of channels for fear of Local Oscillator re- radiation problems imay no longer be necssary. UKM |
TV on different aerial causing interference?
Bill Wright wrote:
"Jim" wrote in message ronet... 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 The aerials were all mounted vertically on a single mast, all with vertical polarisation. In your example, the aerials are mounted on horizontal spars and the vertical separation is greater. Which would be worse for overlapping fields? It's hard to say really, but in general I would have thought that if the dipoles were broadside on there would be more chance of signal passing from one to the other. Bill- Hide quoted text - - Show quoted text - Could be coupling between the two sections of coax running alongside each other, this is likely to be comparable to the coupling between the two antennas. I believe many modern digital tuners use a zero IF technique with the recovered I & Q signals being applied directly to the demodulator chipset. So the avoidance of channels for fear of Local Oscillator re- radiation problems imay no longer be necssary. U&V are the un-weighted R-Y and B-Y in the case of the PAL system. I&Q are near equivelents for NTSC. In eather case you are going to need a Y signal as well. -- Graham. %Profound_observation% |
TV on different aerial causing interference?
"Ian Jackson" wrote in message ... In message , Woody writes "Ian Jackson" wrote in message ... In message , Woody writes "Al" wrote in message 3.1.4... 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 My guess is that it's not been a problem since we routinely left the screening cans off the PC86 and PC88 valves so they ran cooler! -- Graham. %Profound_observation% |
TV on different aerial causing interference?
When this sort of problem occurs, a small one-in one-out amplifier,
followed by an attenuator if necessary, prevents anything getting back up the downlead. Digging up an old thread, but finally got back to the parents. Tried a variable attenuator on it's own. No good. Too much signal loss. Tried a cheap one-in two-out amp on it's own. Perfect. No need for any attenuation as the 'new' TV seems quite happy with way too much signal stuffed into it. Result: Happy parents, cost to me 7 or 8 quid for the amp and a flylead. Thanks for all of the input on this thread, it was really helpful and educational :) Al. |
TV on different aerial causing interference?
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. Replying to myself just to put this one to bed for anyone searching for similar problems. Sorry about digging up an old thread! Tried a variable attenuator on it's own. No good. Too much signal loss. Tried a cheap one-in two-out amp on it's own. Perfect. No need for any attenuation as the 'new' TV seems quite happy with way too much signal stuffed into it. Result: Happy parents, cost to me 7 or 8 quid for the amp and a flylead. Thanks for all of the input on this thread, it was really helpful and educational :) Al. |
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