5 ms·

I don't know how this could even remotely be enforced.

by junon 5y ago

Majromax 5y ago
Superheterodyne receivers (https://en.wikipedia.org/wiki/Superheterodyne_receiver https://en.wikipedia.org/wiki/Superheterodyne_receiver) use a local oscillator to downmix the received radio or television signal for processing at a much more sane, lower frequency. That local oscillator emits its own RF radiation, so it is potentially detectable.
- BenjiWiebe 5y ago
  Correct. However, if using an rtl-sdr by itself to listen to HF, you are utilizing direct conversion which doesn't use an intermediate frequency. I believe the IF is still being generated (?), but it's no longer indicative of what you are listening to.
  - formerly_proven 5y ago
    Direct conversion has no IF but still uses a mixer and a LO, and the LO still leaks out of the input port of the mixer. Because you're directly converting the RF to baseband, LO frequency is the tuned frequency. Unlike e.g. a dual or triple conversion receiver (used in e.g. spectrum analyzers), where the first IF is way above the highest tunable frequency.
  - mhh__ 5y ago
    There is almost definitely something to detect if you brought a van full of RF gear, but it's not like the good old days where it was obvious.
- jasonzemos 5y ago
  Great link as it mentions Radar Detector Detectors. This is actively enforced in the US state of Virginia.
  - tata71 5y ago
    Which is one of very few places radar detectors are against the law in the US.
    - jaywalk 5y ago
      I would love to see it challenged all the way up to the Supreme Court if necessary. These laws seem blatantly unconstitutional, and it's kind of amazing that they've held up for so long.
  - dguest 5y ago
    It gets better than that: there were radar-detector-detector-detectors [1] which were consumer radar detectors that could detect the police radar-detector-detector and shut down. It's tagged as [citation needed] on wikipedia, but the source [2] does mention this as a feature of some radar detectors. I like to hope it's true. [1]: https://en.wikipedia.org/wiki/Radar_detector_detector https://en.wikipedia.org/wiki/Radar_detector_detector [2]: https://web.archive.org/web/20100620150944/http://radar.757.org/VG2.htm https://web.archive.org/web/20100620150944/http://radar.757....
  - eloisius 5y ago
    The lengths highway patrol go to enforce speed limits manually is insane to me. I've never understood why, if speeding is such an important thing to prevent, why don't they use camera enforcement. If you travel between cameras A and B in less than the minimum time it would take at the speed limit, somewhere along the way you were speeding. There's no way around it. You could speed and then travel slower than the limit to average it out, but there would be no point, and enforcement is already spotty. Just send the ticket in the mail, or dispatch a patrol car if someone is speeding recklessly fast. It seems like it would calm traffic, because people would travel the speed limit instead of speeding and then abruptly dropping from 90mph to 65 when they see a cop hidden behind a bridge. I've seen demonstrations that traffic waves cause jams even when there is no problem with throughput, just because someone slammed on their brakes. I'm actually not sure what it'd do to ticket revenue. If there was no way around it because your average speed gets measured, I guess people would stop speeding. Maybe the gambling aspect of it is desirable to governments because if there's a small chance of getting a ticket, lots of people will speed and thus get tickets. If tickets are a certainty, no one speeds and revenue dries up. Do police unions lobby against using this kind of enforcement because it'd mean less cops lurking under bridges for an easy payday?
- junon 5y ago
  Magic. Got it.
User23 5y ago
In the UK you need a license to receive the BBC[1]. And they drive around in vans[2] looking for evidence of unlicensed receivers. [1] https://en.wikipedia.org/wiki/Television_licensing_in_the_United_Kingdom https://en.wikipedia.org/wiki/Television_licensing_in_the_Un... [2] https://en.wikipedia.org/wiki/TV_detector_van https://en.wikipedia.org/wiki/TV_detector_van
- brigandish 5y ago
  I'd be willing to wager that the detection techniques said to be used in the vans are a product of mendacious fantasy (some might say that is par for the course with the BBC), and the actual method used is to simply correlate homes that do not have licences with those that previously had them, and to simply look towards the roof and see if an aerial is present. Ockham's razor and all that.
  - bloak 5y ago
    Analogue CRT television sets emitted some distinctive signals, I think, like the horizontal scan rate of about 15 kHz: https://en.wikipedia.org/wiki/Horizontal_scan_rate https://en.wikipedia.org/wiki/Horizontal_scan_rate That's hardly relevant today, of course.
    - ivanhoe 5y ago
      True, but it's low power signal and it's not an easy job to triangulate on that in say a 12-storey building, 8 apartments per floor, and where everyone has TVs emitting on the same frequency. It makes very questionable the legality of entering someone home based just on that.
      - UncleSlacky 5y ago
        They're not legally allowed to enter your home without your consent, anyway.
        5y ago
jonp888 5y ago
It's the reason that there are no live streams of ATC transmissions online for UK airports. Doing that would trigger some "enforcement".
- mike_d 5y ago
  "No live streams" is a little broad. LiveATC specifically was targeted by Ofcom. GlobalTuners and dozens of other sites have UK ATC broadcasts, they just can't advertise them publicly.

I don't know how this could even remotely be enforced.

by junon 5y ago

I don't know how this could even remotely be enforced.

Superheterodyne receivers (https://en.wikipedia.org/wiki/Superheterodyne_receiver https://en.wikipedia.org/wiki/Superheterodyne_receiver) use a local oscillator to downmix the received radio or television signal for processing at a much more sane, lower frequency. That local oscillator emits its own RF radiation, so it is potentially detectable.

BenjiWiebe 5y ago
Correct. However, if using an rtl-sdr by itself to listen to HF, you are utilizing direct conversion which doesn't use an intermediate frequency. I believe the IF is still being generated (?), but it's no longer indicative of what you are listening to.
- formerly_proven 5y ago
  Direct conversion has no IF but still uses a mixer and a LO, and the LO still leaks out of the input port of the mixer. Because you're directly converting the RF to baseband, LO frequency is the tuned frequency. Unlike e.g. a dual or triple conversion receiver (used in e.g. spectrum analyzers), where the first IF is way above the highest tunable frequency.
- mhh__ 5y ago
  There is almost definitely something to detect if you brought a van full of RF gear, but it's not like the good old days where it was obvious.
jasonzemos 5y ago
Great link as it mentions Radar Detector Detectors. This is actively enforced in the US state of Virginia.
- tata71 5y ago
  Which is one of very few places radar detectors are against the law in the US.
  - jaywalk 5y ago
    I would love to see it challenged all the way up to the Supreme Court if necessary. These laws seem blatantly unconstitutional, and it's kind of amazing that they've held up for so long.
- dguest 5y ago
  It gets better than that: there were radar-detector-detector-detectors [1] which were consumer radar detectors that could detect the police radar-detector-detector and shut down. It's tagged as [citation needed] on wikipedia, but the source [2] does mention this as a feature of some radar detectors. I like to hope it's true. [1]: https://en.wikipedia.org/wiki/Radar_detector_detector https://en.wikipedia.org/wiki/Radar_detector_detector [2]: https://web.archive.org/web/20100620150944/http://radar.757.org/VG2.htm https://web.archive.org/web/20100620150944/http://radar.757....
- eloisius 5y ago
  The lengths highway patrol go to enforce speed limits manually is insane to me. I've never understood why, if speeding is such an important thing to prevent, why don't they use camera enforcement. If you travel between cameras A and B in less than the minimum time it would take at the speed limit, somewhere along the way you were speeding. There's no way around it. You could speed and then travel slower than the limit to average it out, but there would be no point, and enforcement is already spotty. Just send the ticket in the mail, or dispatch a patrol car if someone is speeding recklessly fast. It seems like it would calm traffic, because people would travel the speed limit instead of speeding and then abruptly dropping from 90mph to 65 when they see a cop hidden behind a bridge. I've seen demonstrations that traffic waves cause jams even when there is no problem with throughput, just because someone slammed on their brakes. I'm actually not sure what it'd do to ticket revenue. If there was no way around it because your average speed gets measured, I guess people would stop speeding. Maybe the gambling aspect of it is desirable to governments because if there's a small chance of getting a ticket, lots of people will speed and thus get tickets. If tickets are a certainty, no one speeds and revenue dries up. Do police unions lobby against using this kind of enforcement because it'd mean less cops lurking under bridges for an easy payday?
junon 5y ago
Magic. Got it.

User23 5y ago

In the UK you need a license to receive the BBC[1]. And they drive around in vans[2] looking for evidence of unlicensed receivers. [1] https://en.wikipedia.org/wiki/Television_licensing_in_the_United_Kingdom https://en.wikipedia.org/wiki/Television_licensing_in_the_Un... [2] https://en.wikipedia.org/wiki/TV_detector_van https://en.wikipedia.org/wiki/TV_detector_van

brigandish 5y ago
I'd be willing to wager that the detection techniques said to be used in the vans are a product of mendacious fantasy (some might say that is par for the course with the BBC), and the actual method used is to simply correlate homes that do not have licences with those that previously had them, and to simply look towards the roof and see if an aerial is present. Ockham's razor and all that.
- bloak 5y ago
  Analogue CRT television sets emitted some distinctive signals, I think, like the horizontal scan rate of about 15 kHz: https://en.wikipedia.org/wiki/Horizontal_scan_rate https://en.wikipedia.org/wiki/Horizontal_scan_rate That's hardly relevant today, of course.
  - ivanhoe 5y ago
    True, but it's low power signal and it's not an easy job to triangulate on that in say a 12-storey building, 8 apartments per floor, and where everyone has TVs emitting on the same frequency. It makes very questionable the legality of entering someone home based just on that.
    - UncleSlacky 5y ago
      They're not legally allowed to enter your home without your consent, anyway.
      - 5y ago

jonp888 5y ago

It's the reason that there are no live streams of ATC transmissions online for UK airports. Doing that would trigger some "enforcement".

mike_d 5y ago
"No live streams" is a little broad. LiveATC specifically was targeted by Ofcom. GlobalTuners and dozens of other sites have UK ATC broadcasts, they just can't advertise them publicly.