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cellphone? interference to satellite IF
Some of you might remember me asking if anyone knew which Astra 28E
transponder NASN was on. The answer turned out to be D9S. The frequency is 11623MHz. Today I investigated the complaint that started me on this trail. A very nice US citizen living near here in a large apartment complex had intermittent reception of NASN. No-one else in the block had a problem, but there again no-one else is American, and the other channels in the mux would only be of interest to lunatics. When I asked the analyser to analyse D9S it said that the channel power was just fine, but it refused to even consider decoding the datastream. I turned the line power off, thus disabling the polarity switch at the repeater. Exactly where D9S had been there was a large spike, only a few dB below the transponder power. The IF frequency is 1873MHz. I suspect a local cellphone mast. In theory nothing should get into the TV system thanks to heavy screening, but of course that's theory for you. I walked right round the block with a screwdriver shoved into the analyser's input. The spike peaked at one corner. Above my head was a hideously rigged point-to-point microwave aerial -- one of those things that looks like a length of pipe. Dunno whether that was the culprit or just a red herring. Has anyone any experience of this sort of problem? Bill |
Yes Bill, exactly the same thing here in coventry (bedworth to be precise),
and more interestingly it started at 5pm on a friday and finished between 9-10am on the following monday morning every week, across about 5 transponders, in a very small area, covering about 5 houses (outside this the Sky boxes worked fine) ended up resiting the dishes at ground level (etc.)after an unsuccsefull visit from the RA investigation team who refused to attend when it was actually doing it!! Alan telespeed Bill" wrote in message ... Some of you might remember me asking if anyone knew which Astra 28E transponder NASN was on. The answer turned out to be D9S. The frequency is 11623MHz. Today I investigated the complaint that started me on this trail. A very nice US citizen living near here in a large apartment complex had intermittent reception of NASN. No-one else in the block had a problem, but there again no-one else is American, and the other channels in the mux would only be of interest to lunatics. When I asked the analyser to analyse D9S it said that the channel power was just fine, but it refused to even consider decoding the datastream. I turned the line power off, thus disabling the polarity switch at the repeater. Exactly where D9S had been there was a large spike, only a few dB below the transponder power. The IF frequency is 1873MHz. I suspect a local cellphone mast. In theory nothing should get into the TV system thanks to heavy screening, but of course that's theory for you. I walked right round the block with a screwdriver shoved into the analyser's input. The spike peaked at one corner. Above my head was a hideously rigged point-to-point microwave aerial -- one of those things that looks like a length of pipe. Dunno whether that was the culprit or just a red herring. Has anyone any experience of this sort of problem? Bill |
Yes Bill, exactly the same thing here in coventry (bedworth to be precise),
and more interestingly it started at 5pm on a friday and finished between 9-10am on the following monday morning every week, across about 5 transponders, in a very small area, covering about 5 houses (outside this the Sky boxes worked fine) ended up resiting the dishes at ground level (etc.)after an unsuccsefull visit from the RA investigation team who refused to attend when it was actually doing it!! Alan telespeed Bill" wrote in message ... Some of you might remember me asking if anyone knew which Astra 28E transponder NASN was on. The answer turned out to be D9S. The frequency is 11623MHz. Today I investigated the complaint that started me on this trail. A very nice US citizen living near here in a large apartment complex had intermittent reception of NASN. No-one else in the block had a problem, but there again no-one else is American, and the other channels in the mux would only be of interest to lunatics. When I asked the analyser to analyse D9S it said that the channel power was just fine, but it refused to even consider decoding the datastream. I turned the line power off, thus disabling the polarity switch at the repeater. Exactly where D9S had been there was a large spike, only a few dB below the transponder power. The IF frequency is 1873MHz. I suspect a local cellphone mast. In theory nothing should get into the TV system thanks to heavy screening, but of course that's theory for you. I walked right round the block with a screwdriver shoved into the analyser's input. The spike peaked at one corner. Above my head was a hideously rigged point-to-point microwave aerial -- one of those things that looks like a length of pipe. Dunno whether that was the culprit or just a red herring. Has anyone any experience of this sort of problem? Bill |
Yes Bill, exactly the same thing here in coventry (bedworth to be precise),
and more interestingly it started at 5pm on a friday and finished between 9-10am on the following monday morning every week, across about 5 transponders, in a very small area, covering about 5 houses (outside this the Sky boxes worked fine) ended up resiting the dishes at ground level (etc.)after an unsuccsefull visit from the RA investigation team who refused to attend when it was actually doing it!! So what goes on at weekends that might cause it? How odd. Bill |
Yes Bill, exactly the same thing here in coventry (bedworth to be precise),
and more interestingly it started at 5pm on a friday and finished between 9-10am on the following monday morning every week, across about 5 transponders, in a very small area, covering about 5 houses (outside this the Sky boxes worked fine) ended up resiting the dishes at ground level (etc.)after an unsuccsefull visit from the RA investigation team who refused to attend when it was actually doing it!! So what goes on at weekends that might cause it? How odd. Bill |
On 13 Jul 2004 23:27:31 GMT, o (Bill) wrote:
Some of you might remember me asking if anyone knew which Astra 28E transponder NASN was on. The answer turned out to be D9S. The frequency is 11623MHz. After being down-converted by the (Universal) LNB, then that would be sent to the receiver at 1873 MHz. You should keep in mind that the receiver does not receive the signal at the same frequency as is sent by the satellite. Today I investigated the complaint that started me on this trail. A very nice US citizen living near here in a large apartment complex had intermittent reception of NASN. No-one else in the block had a problem, but there again no-one else is American, and the other channels in the mux would only be of interest to lunatics. When I asked the analyser to analyse D9S it said that the channel power was just fine, but it refused to even consider decoding the datastream. I turned the line power off, thus disabling the polarity switch at the repeater. Exactly where D9S had been there was a large spike, only a few dB below the transponder power. The IF frequency is 1873MHz. I suspect a local cellphone mast. That is highly likely, when 11623 subject to the 9750 L.O would be downlinked to the receiver at exactly 1873 Mhz. However, there is one thing that you can do to get around this problem, provided that you have control over the 22 KHz tone signal in your receiver of course. As the second L.O in the LNB is 10600 Mhz. This means that this 11623 MHz signal can also be downlinked at 1023 Mhz. And watching it at this frequency instead means no more interference. Using a Digibox to do this is unlikely to be helpful, when this receiver only works one way. This could also explain why other viewers do not report this problem, when receivers can switch between the lower and upper L.Os at different points. And 11,623 MHz is within the range when most receivers would consider switching over. In theory nothing should get into the TV system thanks to heavy screening, Many earlier cable installations were far from ideal in terms of screening, where of course that was also before these signals were shared with the telecoms market. I noticed interference myself on the same cable type as Sky's recommended CT100 cable. My solution was to upgrade the cable to CT125 spec (more correctly FT125), when then the interference on this frequency was greatly minimised. Remember that the coaxial cable if the shielding is not good enough will act like a giant aerial. On large early installations, then the cable type could be far from ideal. Anyone fitting coaxial cable these days of less than CT100 spec is really asking for trouble. but of course that's theory for you. The professionals know far beyond simple theory. I walked right round the block with a screwdriver shoved into the analyser's input. The spike peaked at one corner. Above my head was a hideously rigged point-to-point microwave aerial -- one of those things that looks like a length of pipe. Dunno whether that was the culprit or just a red herring. You would have to check the frequency output, but at that frequency it would have to be faulty. Not to mention that by turning it off, then you can see if the problem goes away. Should it be the problem, then quite rightly the owner has to have it repaired, replaced or removed. Has anyone any experience of this sort of problem? Anyone who values their satellite reception and have encountered what happens when the telecoms system shares this frequency range. I noticed my interference problem during analogue reception, when under digital you would simply have blackness. Still my problem was not bad enough to take out digital reception, but I upgraded the cable anyway. Before that time there was no interference... Cardman http://www.cardman.com http://www.cardman.co.uk |
On Wed, 14 Jul 2004 13:19:13 GMT, "Alan"
wrote: Yes Bill, exactly the same thing here in coventry (bedworth to be precise), and more interestingly it started at 5pm on a friday and finished between 9-10am on the following monday morning every week, Sounds like they upped the power to deal with the weekend demand increase. I am not too sure the theory behind that idea, but this is clearly weekend times for the telecoms market. across about 5 transponders, in a very small area, covering about 5 houses (outside this the Sky boxes worked fine) The telecoms market works in mysterious ways. ;-] ended up resiting the dishes at ground level (etc.)after an unsuccsefull visit from the RA investigation team who refused to attend when it was actually doing it!! Resetting the dish is unlikely to help. THIS IS THE CABLE!!! So it would only help if you moved the cable. Upgrade your coaxial cable to a specification with better shielding, when then this problem could well vanish. Cardman http://www.cardman.com http://www.cardman.co.uk |
On Wed, 14 Jul 2004 13:19:13 GMT, "Alan"
wrote: Yes Bill, exactly the same thing here in coventry (bedworth to be precise), and more interestingly it started at 5pm on a friday and finished between 9-10am on the following monday morning every week, Sounds like they upped the power to deal with the weekend demand increase. I am not too sure the theory behind that idea, but this is clearly weekend times for the telecoms market. across about 5 transponders, in a very small area, covering about 5 houses (outside this the Sky boxes worked fine) The telecoms market works in mysterious ways. ;-] ended up resiting the dishes at ground level (etc.)after an unsuccsefull visit from the RA investigation team who refused to attend when it was actually doing it!! Resetting the dish is unlikely to help. THIS IS THE CABLE!!! So it would only help if you moved the cable. Upgrade your coaxial cable to a specification with better shielding, when then this problem could well vanish. Cardman http://www.cardman.com http://www.cardman.co.uk |
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As the second L.O in the LNB is 10600 Mhz. This means that this 11623
MHz signal can also be downlinked at 1023 Mhz. And watching it at this frequency instead means no more interference. This sounds like a very good idea. I just tried it on my analyser and it works. Can a Sky box be persuaded to do this? I have very little to do with them, since my responsibility stops at the wallplate. Bill |
As the second L.O in the LNB is 10600 Mhz. This means that this 11623
MHz signal can also be downlinked at 1023 Mhz. And watching it at this frequency instead means no more interference. This sounds like a very good idea. I just tried it on my analyser and it works. Can a Sky box be persuaded to do this? I have very little to do with them, since my responsibility stops at the wallplate. Bill |
On Sat, 17 Jul 2004 00:06:45 +0100,
lid (Alan Pemberton) wrote: Bill wrote: This sounds like a very good idea. I just tried it on my analyser and it works. Can a Sky box be persuaded to do this? I have very little to do with them, since my responsibility stops at the wallplate. We had a discussion elsewhere that revealed that if you disable the 22kHz switching on the Sky digibox it will continue to receive signals using the low-band IF at least as far as the default transponder (which it normally considers 'high band'). I can't see any way of persuading it to do the opposite, though. Interestingly enough on my web site I sell 22 KHz Tone Generators, that will certainly introduce the missing signal into the line. There is your answer... The only problem then is figuring out the desired tuning frequency in order to manually tune in this station on the higher L.O. To save you the effort, then that is 10,773 MHz. Kind of a long method to get one station, or correctly transponder, but you would certainly get it interference free. I happened to sell one of these 22 KHz Tone Generators yesterday that I remember sending off. It went to a customer in France I believe. Cardman. http://www.cardman.com http://www.cardman.co.uk |
On Sat, 17 Jul 2004 00:06:45 +0100,
lid (Alan Pemberton) wrote: Bill wrote: This sounds like a very good idea. I just tried it on my analyser and it works. Can a Sky box be persuaded to do this? I have very little to do with them, since my responsibility stops at the wallplate. We had a discussion elsewhere that revealed that if you disable the 22kHz switching on the Sky digibox it will continue to receive signals using the low-band IF at least as far as the default transponder (which it normally considers 'high band'). I can't see any way of persuading it to do the opposite, though. Interestingly enough on my web site I sell 22 KHz Tone Generators, that will certainly introduce the missing signal into the line. There is your answer... The only problem then is figuring out the desired tuning frequency in order to manually tune in this station on the higher L.O. To save you the effort, then that is 10,773 MHz. Kind of a long method to get one station, or correctly transponder, but you would certainly get it interference free. I happened to sell one of these 22 KHz Tone Generators yesterday that I remember sending off. It went to a customer in France I believe. Cardman. http://www.cardman.com http://www.cardman.co.uk |
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