TV Detector Vans: Did They Work? ...YES! And Here's How!

I worked as a radio and television technician in the mid-1970s. Back then, we used to have fun building powerful FM transmitters to run small, local pirate radio stations. The German postal service operated so-called radio direction-finding vans—delivery vehicles equipped with rotating antennas—to track down signal jammers or, indeed, pirate radio operators like us. We knew where the vans were parked at night and would secretly attach small, battery-operated transmitters to their bumpers.

my dad worked on them, they were hit and miss, just propaganda scare van. and today totally useless with so many electronic devices about.

So funny, John Stonehouse! The MP who went to prison for faking his own death to avoid a charge of creative accounting on his business ventures as well as being under suspicion of being a spy. Like he should be the minister after people for TV licence evasion.

As a kid I built a simple spectrum analyser using a TV tuner block. Sweeping the tune input and a diode detector on the IF output. I used a mains transformer to generate the sweeping DC for the tune voltage. But the local oscillator would also sweep through the RF frequency, as the IF was only around 39MHz. The LO leakage would then jam the local TVs. But as my sweep was mains derived, and so was the TV frame rate, it would only jam for a fixed point in each TV frame. When I heard parents and neighbours discussing the strange black bands on their TV programs the previous evenings, I realised what had happened. The spec-an did work surprisingly well, for something bodged up by a 14yo.

TV video carriers were AM (Amplitude Modulation). Only the audio was FM.

your problem with this is the fact that regardless of whether it actually worked or not, these vans tended to be staffed by post office employees that were usually heading up to retirement and were given this relatively easy duty as their time with the PO came to an end, I know this because a relative of mine was doing exactly that in the late 70's/early 80'sand he was simply being told to drive around his town in the detector van, pull up in random places for about half an hour or so, just for intimidation, he actually decided that a better use of his time and the detector van, was to take orders for fresh fish, drive over to Grimsby in the van buy the fish, come back and deliver it door to door!

There are a lot of errors in the description. The video signal was not FM (the audio was however) It was negatively modulated vestigial Sideband AM. TVs did not produce a carrier wave, (or even a frequency the same as the broadcast carrier wave, since calling it a carrier wave is complete nonsense) They were superheterodyne radios using a local oscillator at a near frequency to mix with the incoming signal to produce an intermediate frequency to demodulate, These frequencies were standard, so the actual channel could be worked out. This would be possible originally, when there was little other RF around, but seems unlikely (or unaffordable) after TVs had to be built to comply with RF emissions standards, and would be even more unlikely for digital TVs (though there is an HDMI leakage exploit that has been demonstrated). And iPlayer would be monitored at the server end. It was mostly bluff, but not entirely.

For fun I would sometime change my broadband router SSID of my WiFi to 'BBC TV License Detector Van' just to panic the neighbours :)

As an American, this system sounds so crazy to me.

We had TV detector cars like this in Hungary until the end of the 80s. There were 2 TV channels at the time. Channel 2 was only broadcast in the evenings, and there were movies on it. However, the license fee was not expensive, everyone usually paid it. What was funny, looking back, was: I was playing with the old tube radio and I caught a broadcast where short words were being mechanically listed. My grandmother ran into the room screaming and pulled the cable out of the wall. She was afraid that the black car would come and take us to Siberia, because they would sense that I was listening to this broadcast. We heard a Russian number station, as it turned out later. We were not allowed to listen to such things.

A slight correction the video signal was amplitude modulated on a carrier at about 40MHZ. It was the audio that was frequency modulated on a carrier spaced 6Mhz from the video carrier on European sets the audio carrier was at 5.5Mhz and when NICAM stereo sound came in the carrier for that was 6.552Mhz and used a different modulation tecnique. The detector van equipment was alleged to detect a combination of the local oscillator in the tuner and the line scan frequency of 15.625khz for a 625 line system. It has often been said these vans don't work as these signals are very small in amplitude as the local oscillator is enclosed inside a metal can which is the tuner some TV sets also had the IF amplifier stages inside this can as well (Grundig sets in particular). The bit about the light signature could be fact as the light from the TV display does indeed change with the scene being shown bothe in brightness and colour but if the house had thick curtains this would then be difficult to detect. I used to repair TVs before the flat panels replaced the CRTs. I still do the odd TV repair mainly for friends and family.

Only Britain would find the most complicated way to fund the TV.

Rolf Harris got his start at the BBC as a TV detector van operator.

Never seen one of these vans on the road. Ever.

Fundamental error in the explanation as PAL television in the UK used AM modulation of the vision signal which is very different from FM, so incorrect from the outset. I have heard the local oscillator theory which does sound credible and is technically possible. The quote from TV licencing about vans still working dated from 2003, twenty three years ago when there was still analog television in the UK. The idea of a "fingerprint" of light in a TV picture from a television which may be LCD, OLED or even plasma or CRT display technology is nonsense. The real effect of the the television detector van was its presence and visibility, post offices in locations where detector vans were sent saw an increase in TV licence sales, no mention of this in the video. 0/10 for the science museum here I'm afraid.

Yeah, right. Yes, old TV sets used to flicker and maybe that showed someone was watching something but with the curtains closed it never caught me watching Columbo in the front room without a television licence!

This guy worked for the BBC and also did a bit for the One Show on TV licences.

The use of contract labour 🗣️to knock on addresses that don't have a license 🪪...Is how it works ..🙂‍↔️.Detecter Vans have been a running joke for decades 😂

I want to see the "Cat Detector Van"... I hear it could pinpoint a purr at over 100 yards. With Eric being such a happy cat it would be a piece of cake!

They may have shown something but lets face it it was a load of nonsense and still is.