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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 25th Sep 2020, 11:01 pm   #81
Tim
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Default Re: Old TV blamed for modern technology not working

Tv in question was apparently a DVD combo, but not exactly sure how old.
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Old 25th Sep 2020, 11:26 pm   #82
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Default Re: Old TV blamed for modern technology not working

Thinking about the problem it's more like a handshaking problem over a data network, where noise starts to interfere with proper transmission. Sender sends out packages with a checksum and receiver sends back a checksum to verify proper receipt. Only the noise over the network corrupts the checksum that's being returned .So proper transmission is delayed ( and hence a speed reduction) untill both parties can achieve a checksum parity.
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Old 26th Sep 2020, 12:50 am   #83
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Default Re: Old TV blamed for modern technology not working

Quote:
Originally Posted by Electronpusher0 View Post
Quote:
Originally Posted by Techman View Post
Quote:
Originally Posted by high_vacuum_house View Post
May be an opportunity to bring back and re equip the old TV detector vans
Bring them back?

They were never there in the first place!
When I was a student at Chichester FE college, must have been early seventies, they brought a detector van round as a PR exercise.
It had real detector gear but most of the van has laid out with seating so the public could be invited in and be scared into buying a licence.
When our class trooped in the technician giving the talk asked us what we were studying and when he found out it was electronics he put aside the handouts and gave us the technical info instead.

It basically worked by picking up the local oscillator so the operator would have to guess what channel was being watched by the target house, 7:30, must be corrie!
The receiver would be tuned to the LO frequency and the two aerials on the roof would be spaced by motor drives so that they gave a 5 or 7 lobe reception pattern.
The receiver output drove the Y axis on an oscilloscope, the X axis was driven by the vehicle wheels so that as the van rolled past the house the display would move along the X axis.
The van would then drive slowly past the house and as the TV came into each lobe the scope gave a response. The main lobe was at right angles to the van so that as the van passed in line with the TV the scope showed maximum deflection. The operator would press a button as the van passed each end of the house, this gave a marker on the scope. If the main reception lobe showed maximum signal within the limits of the house this was considered evidence that there was a TV operating within the house.
The scope image was recorded by means of a polaroid film

The van crew would then knock on the door and see if the owner would confess when presented with the image.
If not they had no right of entry and had to get a search warrent from the court, which would be granted, the photo being considered sufficient evidence for the warrent. This would take about 3 days and as the technician told us if the owner cannot get rid of the set or buy a licence in those 3 days they deserve to be caught.

It was very limited, quite apart from having to guess the channel it would not give elevation so was no use for flats and as it needed a clear, straight, run past the house it was no good for houses on corners or bends.

Its primary function was to be seen and scare people, during the day they used to park it in the nearest shopping centre or high street.

Peter
Interesting. I've often wondered the details of how they worked. Why would they have to guess the channel? The local oscillator frequency is the receiving frequency plus IF and would be vastly different between band 1 and band 3.
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Old 26th Sep 2020, 1:11 am   #84
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Default Re: Old TV blamed for modern technology not working

As a TLO for GEC Radio & Television, I was called out to a weird one in a line of terraced houses. Owner of a GEC Colour set complained of the picture going to Black and White when neighbour turned on their TV. They had both sets positioned in the same place so there was close coupling via the wall. The neighbour offered to move her set which sorted the problem but I could never understand how one set could remotely turn on the colour killer.
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Old 26th Sep 2020, 2:21 am   #85
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Default Re: Old TV blamed for modern technology not working

My speculation: The colour decoder uses the hsync to lock to the burst. If that circuit picks up the other sets horiontal deflection (which is the strongest radiated signal in most cases), the decoder won't work properly.
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Old 26th Sep 2020, 5:25 am   #86
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Default Re: Old TV blamed for modern technology not working

If the set in Wales is old, it must have been used with a DVB-T set top box.

Signals along fibres can be affected by magnetic fields because specially doped fibre can be used as a flux sensor, but ordinary fibres and the sort of flux which can be generated by something running off a 13A fuse, no, I don't think so.

So whatever the TV was creating had to be disrupting the coppery part of the network between the cabinet and the consumers. Or between the consumers and the exchange. If a whole village is being disrupted then I would think the TV would need to couple into somewhere a lot of the circuits concentrate. Leakage of EMC is normally a 2-way thing, so using a portable receiver to look around for leakage of xDSL 'noise' may point to a vulnerability in the network.

David
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