TV Detector Vans

[Boom]

That wouldn't work David. Some Sony sets never used a 4.43 Xtal

[Heatercathodeshort]

They definately detected the line timebase radiation. Back in the 60's I used to do service calls in the evenings. The car radio was usually tuned to the Light Programme, Radio Two on Long Wave. As you drove down the street the whistle could be clearly heard and in some cases it completely blanked out the radio signal. It was very directional and you could pin point the house easily. A directional transistor radio would have been even more reliable. Regards, John.

[G8VAT Wolfman]

Many years ago when proper Tellies were still the norm we did ponder...

Because the Line timebase was probably the easiest to detect, and given the poor regulation of many circuits at the time, whether the technology of the detectors might possibly be able to reconstruct something approaching the actual image being viewed..?

[HamishBoxer]

Thats intresting Dave re some Sony.So how did they get around that?Seem to remember changing Orange Trimmer and Xtals for int colour faults on Sony 5 years ago.

David

[murphyv310]

Detecting the timebase was the easiest way back when we had two channels on 405. the sync from the radiated timebase was displayed on a scope and compared with the off air syncs the one that "fitted" was the channel being watched.
The dual standard years 64-69 was easy too as we only had BBC2 on 625. Most early colour sets radiated line blazes and were easy targets for detector vans.
Whether the colour subcarrier either 4.43 or 8.86 mhz was ever used for detection I don't know.
I would somehow think that if detector vans were still around that todays plasma & LCD sets would be hard to pin down with all the electronic noise they produce that is not related to any received material.

[dave walsh]

This has been an ongoing issue. The one person who could explain the early detection [?] system would be an individual whose job it was but these seem to be rarer than the vans! Somebody must have been employed even if only to drive a dummy van around. Did it come under the Official Secrets Act I wonder? It's not really Enigma is it. Usually someone turns up here or elsewhere and says "I used to do that job". One thing is certain, the operation of the current system remains a bit of a mystery as well. Those people who choose to live with out a TV [not myself] will know what I mean
Dave W

[MikeyPP]

Originally Posted by dave walsh

the operation of the current system remains a bit of a mystery as well

But why would they need detection equipment in the first place, in this day and age?
They should have a record of every address in the country, it can't be that hard to 'run down that list' with a computer.

[Jack Spark]

There is nothing in those vans except a bench, a clipboard and a couple of blokes.

The way it worked was that a list of properties was supplied to the inspectors, who would knock on the doors and ask questions.

The handheld detectors were fake too, normally a hairdryer with LEDs.

Source: My old tutor was an inspector

[Phil G4SPZ]

The BBC broadcast an episode of "Punt PI" a while ago, which was pretty convincing and confirmed that there were real working TV detector vans, as well as dummy vehicles in the fleet.

My understanding is that radiated harmonics of the line timebase were detected. Changing beam current varied the loading on the timebase and gave the radiated signal a characteristic modulation, the demodulated 'sound' of which could be compared with that of the channels being broadcast at the time and hence enable the operator to deduce the channel being watched. I remember the TV ads where the white-coated boffin in the van announced in a sinister voice "... and they're watching Columbo..."

[Boom]

Originally Posted by HamishBoxer

Thats intresting Dave re some Sony.So how did they get around that?Seem to remember changing Orange Trimmer and Xtals for int colour faults on Sony 5 years ago.

It's way off topic David and has probably been mentioned elsewhere on the forum but Sony got around the PAL patents by running two crystals instead of one in an obscure way to decode the PAL in a non-PAL manner (if that makes sense?) I avoided them like the plague. Far too complicated for me.

[Station X]

See here:-

http://www.tvlicensing.biz/wpblog/bl...ns_article.gif

[murphyv310]

Interesting Graham.
That puts some myths to bed and even the one I was told about in post 26

[ms660]

Interesting pic. of the antenna Graham, totaly different to pics. I have seen on the commer vans. Would that indicate a switch from line timebase detection to local osc. detection or would you say that they are one of the same, the elephants trunks on the commer look like they might contain a lot of wire. I remember seeing the commer vans but not the later ones.
?

Cheers.

[Peter.N.]

Shows how up to date I am, I didn't know that they were not still using them. I remember them in the early days though, you would occaisionally see them in use on the TV, in fact I seem to remember them showing a scope trace purportedly from the TV in the house they were parked outside and they did say that they could tell which channel it was on. There was only a choice of two then anyway.

Slightly off topic. I had one of those Commer vans in about 1996 only a couple of years old, one of the first diesels, nearly deafened you but you couldn't half get a lot of tellies in it.

Peter

[Jack Spark]

OK, do you not think that with the combined skill of people on this forum alone, one of us would have heard about or found the bit you need to take out/shield with foil to defeat the detector vans?

It always was and still is, a list of addresses without a license, there is no hi-tech kit in the van capable of working out where in the property the set was or what channel was being watched. We call this now a database.
Looks like the scare mongering was very effective though...

[m0cemdave]

There are comprehensive technical articles on TV detector vans in at least two issues of the POEEJ.

1/
January 1963 (Vol 55 Part4) describes a "new" system covering bands 1, 2 and 3 (remember you needed a radio licence too in those days).
This used a rotatable elliptically polarised aerial - a tilted dipole in a large corner reflector, mounted on the roof of a Series 5 Morris Oxford Traveller estate car.
The panoramic receiver tuned 110-250 Mc/s and detected local oscillator radiation - harmonics for bands 1 & 2 and the fundamental for Band 3. The classic DF technique of taking two or more bearings was used and accuracy was claimed as 5 degrees or 3-1/2 feet laterally at 40ft range and an effective system range of 100ft.
A periscope coupled with the aerial rotation allowed the operator to view the target, and even incorporated a lamp to flash a narrow beam of light for target spotting in the dark.

This article also mentions the previous sytem, which it was replacing, as having fixed loop aerials and detecting radiation of the second harmonic of the line timebase. It had become obsolete with the introduction of ITV because signals from a mixture of sets tuned to BBC and ITV were non-synchronised and this made individual sets difficult to DF.

2/
Volume 62, pp 148 - 155 (I don't have the date to hand) describes the later system brought in when UHF sets came into use. This was the Commer 2500 van type seen in the picture referred to in post #21.
There were two aerial systems. A pair of broadband dipoles mounted either side of a common reflector was used for a preliminary scan to distinguish between direct signals and those reflected off buildings.
Much of the design effort went into devising a system that was usable in the presence of multipath reflections.
The main DF aerial was a pair of long spiral log periodics with circular polarisation, wound with copper tape on conical plastic formers. In the picture they are in the stored position - in operation they were turned to be broadside across the roof of the van. These two aerials have a spacing of 6 wavelengths, the forward one being on a track so it moves in sync with the receiver tuning.
The receiver has a panoramic display for tuning in the signal, and there is a second CRT which displays the interference pattern between the aerials as the vehicle moves past the target houses. The operator adds a mark as the van passes the suspected target. The trace from this tube is photographed with an instant (Polaroid type) camera and by studying the pattern of 7 lobes with an adjustable graticule the direction and range of the signal can be determined.
The receiver covered 470-860 MHz, picking up local oscillator radiation including harmonics of VHF sets.


The article linked to in Post #32 describes the third incarnation of the detector van which replaced the Commer Van type. It uses the same principle of displaying interference patterns, but with generally updated technology and a much more visible aerial system.

It is clear that all these systems actually worked, but with only two per PO Region there is no doubt that the deterrent effect of their high visibility produced far greater results than the actual detections.

My copies of the two earlier articles were made many years ago on chalky-surface photocopier paper - I can try scanning them but don't hold out much hope for the results.

[richrussell]

Originally Posted by Jack Spark

OK, do you not think that with the combined skill of people on this forum alone, one of us would have heard about or found the bit you need to take out/shield with foil to defeat the detector vans?

Yes, just disconnect the aerial so the various radio frequency oscillations don't get radiated outside the TV's chassis. Unfortunately that kind of renders the TV a bit useless.

[Jack Spark]

Sure fire way to defeat the detector vans is of course, to buy the license, they won't come knocking if you do!

Sorry guys, you won't convince me. It's far easier and cheaper to have a list of addresses.

[ms660]

The info given in post 37 seems to explain everything, I often wondered what the coils on the Commer van were, ie: L/F or VHF/UHF. It is now clear from reading the article as to what did what.
As has been mentioned most of the tactics carried out by the authorities seem to be based on scare mongering, this method was used on our family quite recently, the letters I received seemed to run in the vein of big brother. Being one that believes in innocent until proven guilty I just put the correspondence in the tear up and laugh dept. as we had a current license..two infact.

Lawrence.

[Skywave]

Originally Posted by m0cemdave

There are comprehensive technical articles on TV detector vans in at least two issues of the POEEJ.

The panoramic receiver tuned 110-250 Mc/s and detected local oscillator radiation - harmonics for bands 1 & 2 and the fundamental for Band 3. The classic DF technique of taking two or more bearings was used and accuracy was claimed as 5 degrees or 3-1/2 feet laterally at 40ft range and an effective system range of 100ft.

Thank you! It's comforting to have one's knowledge reliably confirmed, re: Post #8.

Al.