Television detector
in [Basics]
|
Prev: A Better Quality AM FM Receiver
Next: CERN. LHC. The time needed to grow is from 1000 seconds to 1000days. The Earth can already be pregnant now.
From: John Tserkezis on 29 Mar 2010 19:57 Frederick Williams wrote: > I haven't heard much about television detector vans lately but we used > to be told that they could detect a television even if it was switched > off and they could even tell which room it was in. > > How do such detectors work? > [I know nothing about electronics but my guess is that televisions > contain circuits that resonate at characteristic frequencies*. When > those circuits have electro magnetic radiation of those frequencies > directed at them, they resonate and re-emit those frequencies and such > emissions can be detected. Something like that. > * I'm using the phrase "characteristic frequencies" loosely.] They don't apply so much anymore, mainly because of technological changes. CRT displays, have a number of deflection coils that direct the electron beams to where it's supposed to go. The coils that do this were driven by the analogue video stream, and the signal is easily discernible by relevant radio receivers and directional antennas. LCD displays don't use such driving technology, so can't be sensed with any real accuracy. Same goes for PC tuner cards that translated the TV display to a different resolution even though you may have a CRT monitor attached to the computer. However, doing that (TV vans) proved expensive. The more reliable method, was to look up the database of who's already paid up, assume that *everyone* has a TV, and just doorknock asking why they haven't paid up yet. The usual suggested course of action is to avoid them (so they need to come back at a later time, hopefully getting tired of the exercise), or leave them at the front door (there is no legal requirement to bring them in) and simply state you do not watch the BBC (which are the only channels legislated by these fees). Of course, if you don't have a TV, you could invite them in and show them (they'll take note and not bother you again). Or if feasible, hide the TV, but might prove difficult if you have a 240" monster hanging off the wall. PC attached tuner cards are more difficult to prove, they're not immediately visible, and the guys in suits are not rocket scientists, and if it doesn't look like a TV it probably ain't a TV. If you really *don't* watch the BBC, good luck to you, you're going to have a fun time trying to prove it.
From: Jasen Betts on 30 Mar 2010 03:27 On 2010-03-29, Frederick Williams <frederick.williams2(a)tesco.net> wrote: > I haven't heard much about television detector vans lately but we used > to be told that they could detect a television even if it was switched > off and they could even tell which room it was in. > > How do such detectors work? dunno. it's pretty hard to detect a TV that's turned off. > [I know nothing about electronics but my guess is that televisions > contain circuits that resonate at characteristic frequencies*. Old style CRT tvs emit emit electromagnetic waves magnetic waves from that magnets that control the vertical and horizontal scanning of the electron beam. To detect LCD tvs they probably use a directonal microhone and listen for the audio track of the TV shows. --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: Phil Allison on 30 Mar 2010 06:08 "Frederick Williams" > >I haven't heard much about television detector vans lately but we used > to be told that they could detect a television even if it was switched > off and they could even tell which room it was in. > > How do such detectors work? ** Only details I ever read involved picking up spurious local oscillator ( ie VHF ) radiation from the TV set emitted via the owner's antenna using a directional loop on top of a van. Don't think it has been done much since the 1960s. ..... Phil
From: Frederick Williams on 30 Mar 2010 14:07 John Tserkezis wrote: > If you really *don't* watch the BBC, good luck to you, you're going to > have a fun time trying to prove it. This hints at some misunderstandings. -- I can't go on, I'll go on.
From: Baron on 30 Mar 2010 16:09
John Tserkezis Inscribed thus: > If you really *don't* watch the BBC, good luck to you, you're going > to have a fun time trying to prove it. Actually, a few years ago a local radio ham got prosecuted for not having a TV license. He ended up in court and proved his case. I don't remember the details but it ended up in the local papers and eventually made national news. I do recall that the whole episode made the TV enforcement people look quite silly. -- Best Regards: Baron. |