For the countries which need Radio and TV licenses. How TV Detector Vans work...

[pdenisowski]

Would that even be possible (detecting someone's TV receiver IF frequency from far away)? I doubt it.

That worked for very old tvs (Unshielded wooden box full of radiating wires), I doubt they can sense and LO or IF frequencies in modern tvs.

Oh, with the right equipment you absolutely can detect (and DF) an LO / IF from a significant distance away - I've personally done this many times. 

It's also not an uncommon application:  how do you think police catch people illegally using radar detectors?

[pdenisowski]

To me, this falls in the same category as "yepper, them satellites can read your license plate from space!" misconceptions.

I was told that they used hundreds of vans that drove around with equipment that could monitor the IF frequency of people's TVs and from the frequency they could tell what channel you were watching. 

this is approaching tinfoil-hat territory.

I'm fairly certain it's never been applied to TV licensing or viewership studies, but it absolutely is possible to see what someone is watching from outside of their home - just use a TEMPEST receiver 



https://www.rohde-schwarz.com/us/products/test-and-measurement/tempest-tests/rs-fswt-test-receiver_63493-310144.html

[Postal2]

I'm fairly certain it's never been applied to TV licensing or viewership studies, but it absolutely is possible to see what someone is watching from outside of their home - just use a TEMPEST receiver 

I wondered who this swindling trick was aimed at. Clearly not the specialist. That means his boss. We elect as bosses those idiots who cannot do useful work.

This can be clearly seen in the history of Space Shuttle Challenger.

[TimFox]

Some confusion here:  there can be enough radiated power from a local oscillator (LO) in a superheterodyne receiver to be detectable with appropriate equipment nearby, but the power in the intermediate-frequency (IF) amplifiers is not likely to radiate.

A typical double-balanced mixer, driven by +7 dBm into the LO port, has 50 dB isolation from LO port to RF (input) port.  That's -43 dBm leakage (50 nW), but there is more power circulating in the oscillator itself.
The CRT TV sets of my youth were not particularly well-shielded, usually in a plastic housing.  Also, the input mixer was not double-balanced.

Radar detectors use simple diode mixers from their receiving antenna, driven by a suitable local oscillator, where the isolation is much worse.

TEMPEST is an interesting concept.  Modern equipment must pass emissions testing to avoid interference with other systems, but TEMPEST is a tighter security specification for when the emissions might contain information of strategic value.
When I first read of it, one had to show a need-to-know to find the actual specification, and ones supervisor could not access the specification unless he showed his need-to-know.

[coppice]

TEMPEST is an interesting concept.  Modern equipment must pass emissions testing to avoid interference with other systems, but TEMPEST is a tighter security specification for when the emissions might contain information of strategic value.
When I first read of it, one had to show a need-to-know to find the actual specification, and ones supervisor could not access the specification unless he showed his need-to-know.

That's true of most defence related specifications. The basics of TEMPEST are not classified, as the basics are just screen, screen, screen. The details are classified.

[coppice]

I'm fairly certain it's never been applied to TV licensing or viewership studies, but it absolutely is possible to see what someone is watching from outside of their home - just use a TEMPEST receiver 

Maybe they could start using it to detect people watching BBC TV from https://www.bbc.co.uk/iplayer

I first saw a demonstration of remote viewing of a raster scan image in the 1980s, when we were first required to get serious about TEMPEST compliance. That was with a CRT, and I think the receiver was picking up radiation from the tube itself. What are they picking up strongly enough to reconstruct the raster from an LCD display?