h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

How do TV detector vans work??

is there any tech to stop/block them or to spot them???

placebo effect.

The old style cathode ray tube televisions and computer monitors gave off so much electric and magnetic radiation that you could reproduce on a screen inside the van what was showing on the TV/monitor, a fact which shocked many banks who thought their security was good.

But it's unlikely they can detect modern flat-screen televisions.

""The old style cathode ray tube televisions and computer monitors gave off so much electric and magnetic radiation that you could reproduce on a screen inside the van what was showing on the TV/monitor,""

so sat in a van outside a block of flats, all of them with a telly on, on a saturday night, could you actually tell which telly was in which flat???

they *could* do it.
They didn't though. Tomorrow's World did a test once and yes, you could pick up what was on a CRT monitor, but the tech was hopelessly experimental.

No doubt such technology exists, but if the Beeb ever did have any such vans (and that is highly debatable*) they were few in number. They worked more from random visits, recent moves and known temporary accommodation and simply scaring you into thinking they exist. Nowadays, at least in England, any sale of a new telly or TV receiving equipment gets your details sent off to them so they can check their database.

* an interesting read:
http://www.bbctvlicence.com/Detector%20vans.htm

TV equipment detection.

The local TV transmitter emits signals at around 500MHz. The same frequencies are sent by satellite and cable systems.

For your TV or PC to use these signals, two Local Oscillator frequencies must be generated by your equipment to enable the pictures and sound to be viewed and heard.

It is these LO frequencies that your equipment generates that Detector Vans can pick up. The Video Frequency is about 450Mhz. The Audio frequency is 495MHz. A secondary beat oscillator is used to produce a 365KHz audio frequency.

You can see that your equipment is far from silent. Although the sinnals may be very weak, they are still detactable.

The Tansmitter may put out many Megawatts of power, but it only takes microwatts of received power to trigger the Local Oscillator in the TV equipment.

That is how the detector van can even tell which channel you are watching!



GT

but how accurate is its DF capabilities

can it distinguish where a tv is inside a building, which side of a party wall the equipment is, etc???

if a whole block of tvs are all on the same channel can they pick out one individual tv or would they just be washed out with all the signals???

""It is these LO frequencies that your equipment generates that Detector Vans can pick up. The Video Frequency is about 450Mhz. The Audio frequency is 495MHz. A secondary beat oscillator is used to produce a 365KHz audio frequency. ""

so if you had a "black box" pumping wattage out on 450, 495MHz. and 365KHz. you could jam detector vans???

THAT! would swamp 'em, Taff!!!



GT

how come they are'nt available???

you can get all sorts of dodgy speed canera/radar trap blockers??

Detector vans & such...

I was at Whitehall communications centre for a while, back in the mumbleties. I got there at the end of an upgrade phase.
The story was that the ungodly had been found tuning in to the plain language keying (pre-encryption).
Can't verify, but it seemed not completely unreasonable - and the upgrade was true enough.

is that the ungodly who could DF an active prestle in 3 sec. and drop a counter battery barrage on you in less than a minute???

Not allowed to tell you

(what's a prestle?)

the talk/transmit switch on a radio

Oh dammitt, that pressle.

Probably, yes.

yes the red menace were very interested in our communications

the all arms school of radio was just outside hull and there was a russian trawler of one type or another allways parked in the harbour at hull, allways had more antenna than nets about it

Aye, and didn't they have a turn of speed.

Ringed by half a fleet of various vessels & through 'em like a dose of salts.

stop!!! i'm getting all missty eyed for the old nemesis

they say you are judged by your enemies

no wonder we are on a downer now, our enemy is a bearded old man sat in a cave in the armpit of the world

how the mighty have fallen

Amen

Of course now they just use a database to see which properties are not listed as having a licence.