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Intermittant RF spikes all the way across VHF & UHF band
"Andy Dee" wrote in message ... -GB-Carpy wrote: Did the nursing home job today, and got the headend all sorted out, perfect signals coming in & out, fine tuned with filters so signals are spot on across all TV points etc BUT there are random RF spikes occuring all the way across the UHF band (and below) which are trashing some of the DVB-T signals quite badly and causing 2 parallel lines with sparklies to come up on analogue stations every few seconds. Are you anywhere near the coast? (Foreign) Military radar can do this. A Nowhere near the coast, and nowhere near a barracks. There's a fire station about 500m away, but the headend signals are clean as a whistle. It's only present on the old coax cabling in the building. |
Intermittant RF spikes all the way across VHF & UHF band
"-GB-Carpy" wrote in message ... Nowhere near the coast, and nowhere near a barracks. There's a fire station about 500m away, but the headend signals are clean as a whistle. It's only present on the old coax cabling in the building. It's going to be mains-borne very likely. You're going to have to switch circuits off one by one. By the way, a friend asked me to visit his dad, who is in a nursing home, to 'tune his telly in and generally sort things out for him.' The signals available from the wallplate were very poor. The analogue and digi signals were at very differing levels but in general were too low by a large margin. The analogue channels had bad ghosting. There were various unwanted signals all the way from 10MHz to 900MHz, most of them at VHF. In particular there was a huge spike of something or other centred on 48.80 MHz. I should have checked it out and found out what the modulation was, but I didn't bother. It was 30dB above any signaI, and I'd guess that the installers had found themselves unable to obtain a reasonable output level from the main amp because when they increased the gain everything would go tits up. They would, of course, be unaware of the cause. I did what I could then went and found the manageress and explained my problem. Together we checked a few other rooms, and found them no better. She promised to 'get it fixed'. I eagerly await the outcome. Bill |
Intermittant RF spikes all the way across VHF & UHF band
"-GB-Carpy" wrote in message ... Did the nursing home job today, and got the headend all sorted out, perfect signals coming in & out, fine tuned with filters so signals are spot on across all TV points etc BUT there are random RF spikes occuring all the way across the UHF band (and below) which are trashing some of the DVB-T signals quite badly and causing 2 parallel lines with sparklies to come up on analogue stations every few seconds. I've watched these on the analyser, and they appear totally random. They go up to around 48dBuV sometimes, and seem to occur in blocks of about 50mhz across. They look like a group of 7 or so analogue channels but without the sound carrier. These signal are definitely not coming in via the headend and therefore can't be blocked. They occur approximately every 2 seconds, in varying strength, and at varying frequencies right the way across the UHF band and all the way down to 50mhz. With the headend completely disconnected they are unchanged, so must be eminating from somewhere in the building. The coax cabling installed is pretty ropey RG6 type with no copper tape and limited braid, but short of rewiring the lot (80 odd rooms) I want to try and narrow down the possibilities as to the cause. Anyone aware of any systems in a nursing home that would cause this kind of spiking? They've got all the usual nurse call systems / fire door auto close systems but they assure me these are all hard wired (I haven't checked though). The lift motor is central in the building, but doesn't seem to correspond in any way to the RF spiking (spiking still present even when lift not in use - lift in use has no effect in spiking etc). It looks almost like an earth loop fault with the sparklies but I'm guessing that it's just one or several of the cables are run alongside power cabling or near to a thermostat / something thats giving out a healthy dose of RF. We certainly can't find it in any void / riser / ceiling so it might not be possible to solve it anyway, but at least if I can narrow it down it would help. It's just annoying because the signals are spot on now, with excellent power, BER & C/N then along comes the RF spike and trashes it all every few seconds. Any pointers? Yes, maybe. This must be over 20 years ago, and not in a nursing home, but in old peoples sheltered flats, the interference was short pulses that drove the TV signal into cross-mod in narrow bands on the screen, it affected all flats and several if not all channels. My visit was to the TV of one resident, but as soon as it became apparent it was an aerial problem I asked to see the head-end even though it was not my responsibility. As soon as the warden opened the cupboard I felt I could see the problem; some sort of transmitter was mounted next to the head end amps, with a thick coax connected with a PL259 that took the same route as the TV aerial downlead. It turned out that the Tx was part of a system called Pocket Master whereby the warden could look after several sites and be paged when a resident pulled a red cord or pressed an alarm button. Anyway she let me turn it off and of course the interference disappeared, so I gave her the obvious advice and left. -- Graham. %Profound_observation% |
Intermittant RF spikes all the way across VHF & UHF band
"Graham." wrote in message ... This must be over 20 years ago, and not in a nursing home, but in old peoples sheltered flats, the interference was short pulses that drove the TV signal into cross-mod in narrow bands on the screen, it affected all flats and several if not all channels. My visit was to the TV of one resident, but as soon as it became apparent it was an aerial problem I asked to see the head-end even though it was not my responsibility. As soon as the warden opened the cupboard I felt I could see the problem; some sort of transmitter was mounted next to the head end amps, with a thick coax connected with a PL259 that took the same route as the TV aerial downlead. It turned out that the Tx was part of a system called Pocket Master whereby the warden could look after several sites and be paged when a resident pulled a red cord or pressed an alarm button. Yes, well at about the same moment in history I put a system in a new sheltered scheme. A few weeks later I got the call from the owner that my aerial system was a load of ****e. The ******* intercom men had put some sort of long end-fed colinear thing on my aerial mast, with the top of it between the elements of my aerial. Why they felt the need to put it right up there I don't know. I find that these guys don't give a damn, and know bugger all. Only this week I went to one and they'd put their little whip aerial in the loft right next to a huge steel water tank. I casually enquired of the warden, who had the little dongle thing on a cord hanging from her neck, whether it worked. "Only on that side," she said, pointing along the corridor in the direction where you expect a whip with a steel tank behind it to work. I recently saw one of these little end-fed things fixed outside above the flat roof by means of being cable tied to an aluminium fallpipe, and with no waterproofing on the PL259, and what looked like 25m of RG59 loose on the roof just below it. Bill |
Intermittant RF spikes all the way across VHF & UHF band
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