Nice article, reminding me that I used to know it was possible to detect TVs (whether it was done in practice in any large scale, I can't say)
But I have lost count of the people who insisted that "it wasn't possible". Mainly people who knew f*ck all about radio technology.
It was possible just very hard and not very successful.
Most detector vans were dummies.
All they needed was a data base of addresses without a TV licence.
I've even used a hand held meter in an office building. It worked.
even harder
I suspect many of them were just mock ups with cones on the top but they could in principle detect the re-radiated intermediate frequency of the classic TV receiver. These days they just knock on the door of anyone who doesn't have TV license.
When I was at university the research group I was in had a project to develop kit that could read the display of a non Tempest proof VDU remotely. The hard part was isolating one unit amongst many rather than getting a signal. The beam current variation and scan coils were enough. It helped that back then most VDU displays were mains synchronous.
Jethro_uk formulated the question :
It certainly was possible, in the analogue /CRT era, because I did it. It was even possible to determine which channel as TV was tuned to. Was it practical to do, with so many TV's around and turned on - probably not, it was intended as more of a frightener, to have people pay up.
bloody time base noise every 17 or 18 Kc/s pain in the arse ....
Day 0. real detector van spends a a whole day and 5 people are prosecuted. Day 30 cases come to court. Local paper features cases and fines. Day 31 fake detector vans seen everywhere. Job done
Hmm, I wonder what UK organisation could possibly have a 'need' for that ?.
I remember a story where FX? dealers at one city bank realised they could see what rates their rivals in an adjacent tower block using a decent pair of binoculars, or similar. Then they could pre-empt all their deals.
Many years later we learned that the main inter-bank lending rates were just being set by all the banks just 'cooperating', never mind actual spying.
You could do it with a directional antenna if UHF - if you can target individual premises. Probably a lot harder in a block of flats.
Some work has been done on RF leakage from VGA/DVI/HDMI cabling and TFT panels - you can do it in lab conditions, but possibly not on the street. On CRTs the deflection coils were quite chatty on RF.
The other way which still works quite well today is to use a sensitive photodetector and pattern-match the brightness signature of the visible light with that of broadcast channels. On a CRT you can see the beam-scan and read out the colour of each pixel (give or take some smearing). On an LCD I think you can still see the frame-to-frame brightness which would be enough to match (eg) all the Freeview channels.
Of course, the most hardened operatives employ counterintelligence techniques - they close the curtains.
Theo
Their acronym at the time was PSDB. A bit like the Avengers/Q for kit.
I expect GCHQ already had their own classified version by then.
There was a thing called a Tele-Fi. Picked up IF radiation without any direct connection and turned it into an audio feed to your Hi-Fi. To get round the danger of many TV sets having live chassis - and well before the makers provided a way of connecting peripherals to a TV.
So it appears. I had a pal in his nineties who had a yearly battle over his not having paid the licence fee.
PA
when us oldies got free licences, you still had to register and declare your age. You were then issued with a licence.
Of course, if your friend didn't have a tv that's a different story.
He did - every year - and received a "we won't bother you again" reply.
Not, by any means, a singular experience - I expect.
PA
In message <ruoso8$lbb$ snipped-for-privacy@dont-email.me, Jethro_uk <jethro snipped-for-privacy@hotmailbin.com writes
"The United Kingdom is somewhat unique in the world for requiring those households which view broadcast television to purchase a licence for the privilege."
This first sentence is far from being true (as a quick Google will reveal).
I certainly recall a TV programme (probably back in the 80s) that showed how radiation from an office block could be received in a van in the street on (I'm pretty sure) a CB radio, and displayed on a video monitor.
In message snipped-for-privacy@davenoise.co.uk>, "Dave Plowman (News)" snipped-for-privacy@davenoise.co.uk> writes
In the early 80s I made something similar for a works colleague. It was just a pick-up coil near one of the 6MHz sound IF transformers, fed to a double-balanced mixer, and crystal oscillator to convert it to the FM radio band. It worked perfectly.
I was invited in one for a demo in this very street during the analogue days. They had local oscillator detection, timebase detection and a hand held unit they went to houses or flats with to localise the sensing. The thing was though, that on average it was enough to park up for a couple of hours and do nothing at a weekend to induce the non payers into action as in the main they already knew which addresses had a licence by that time. Brian
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.