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Comment by LeoPanthera | Hacker News Reader

It is worth pointing out that you do not need an amateur radio license to receive signals, and indeed transmitting is not necessary for this experiment.

Any shortwave or "HF" radio will do. A simple receiving antenna for the HF band is simply a length of wire, as long as possible, and as high as possible.

WWV and WWVH transmit on 2.5, 5, 10, 15, and 20 MHz. (Though 2.5MHz is outside the HF band and difficult to receive with most radios.)

If you live on the US west coast it is often possible to receive both, especially at night, which is why their signals are offset in time.

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> It is worth pointing out that you do not need an amateur radio license to receive signals, and indeed transmitting is not necessary for this experiment.

I don't think that's true everywhere. There is a reason that at least in the 80s/90s, scanners were exclusively sold as "export equipment" in Germany, meaning you were not allowed to buy them for use within Germany. (Don't know if that's still the case.)

They still were advertised next to all the other non-export equipment in consumer electronic store catalogues, just with a warning. I would be shocked, shocked, if there ever were any customers who bought such a scanner without the explicit intent to export it to another country.[1]

[1] I didn't, like actually didn't. Not only was I too young to have that kind of money, at that age I actually thought using one might get me into serious trouble (I have no idea how).

A scanner and a shortwave receiver are not the same thing.

I don't know if listening to this particular signal is legal or not in Germany or anywhere else, I'm just pointing out that for the general case (as I read OP's sentence) it may well depend on the jurisdiction.

The only countries as far as I know that banned shortwave reception were the former eastern block countries and other similar regimes.

Reception of the entire HF band is legal globally, as defined by the ITU. You don't need a scanner to receive shortwave radio, and in fact most scanners can't receive shortwave radio.

ITU doesn't get to decide what's legal in countries. If Cuba wants to tell you it's illegal to listen to Voice of America on HF, they can.

ITU just helps countries agree on uses for spectrum and conventions for its use.

The ITU defines what the bands are, but of course not the legality of using them.

OP said you don't need a license to "receive signals". As far as I know that's not correct. Maybe OP meant specifically these signals, but that's not how I read it, and it's worth pointing out anyway.

> at that age I actually thought using one might get me into serious trouble (I have no idea how).

Aber es war streng verboten!

So, my advice is: if is not legal to receive SW signals in your country: Build your own receiver if needed, but make a point of DO receiving SW signals and try to help as much people as possible while you make sure the State knows people are making it without letting know WHO is doing it.

>as long as possible, and as high as possible.

Caveat about 'long as possible' (for general shortwave listening): Once the antenna is over a half wavelength long at the operating frequency (10MHz, one wavelength is ~~ 100 feet, 30 meters), it becomes increasingly more directional along its axis. (Longer still, even more directional.) This may dampen the signal amplitude for signals coming in 'off the side' (compared to a dipole at least).

If I'm not mistaken in the UK you actually need a licence to listen to some frequencies. I may be misremembering but it always struck me as rather Sisyphean the moment I bought a cheap SDR.

Ok. Good luck enforcing that.

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

Superheterodyne receivers (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.

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.

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.

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.

Great link as it mentions Radar Detector Detectors. This is actively enforced in the US state of Virginia.

Which is one of very few places radar detectors are against the law in the US.

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.

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

[2]: https://web.archive.org/web/20100620150944/http://radar.757....

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?

There are legitimate reasons why someone would go faster than the speed limit (safety) that your simple 2 camera setup would not be able to understand.

Could you elaborate on some of the safety reasons for exceeding the speed limit, to help me understand?

We use average speed cameras in the UK to enforce temporarily reduced speed limits during road repairs on the motorways. It seems to work quite well, it certainly feels like most people adhere to the reduced limits.

Personally, I am aware that if I speed (for whatever internal justification I convince myself of), I just need to reduce my average speed by the time I pass the next camera (they're big and yellow and deliberately conspicuous so drivers know where they are).

Health emergencies or something like that. Though I think it'd be pretty straightforward to say "hey I was going to the hospital, overturn this ticket please" after the fact.

I’ve never had an officer understand my legitimate reason either, and even if they had, the time spent checking my ID and running insurance would far exceed whatever time I gained by speeding.

In a state I lived in, these kinds of camera-based enforcement of vehicle laws were ruled unconstitutional (state constitution). The argument was that traffic laws apply to the person driving the car, not the car, and it's too difficult to tell from videos who is driving the car. There were probably other arguments against them but basically the state supreme court decided there was no way a camera could establish evidence at the level of certainty needed.

It's odd now that I think of it because traffic cameras used for other reasons have been used in felony investigations (eg, murder). My guess is in those cases they have to establish that the person being charged was likely in the car?

I think it's the automatic charging aspect of it.

In Croatia, the owner of the vehicle is responsible to identify the person driving. Otherwise, he pays a fixed fine.

That seems reasonable 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.

I don't know about the US, and I suppose it varies between states anyway, but in the UK that's exactly how it works on our motorways and some larger dual carriageways.

> The lengths highway patrol go to enforce speed limits manually is insane to me.

Enforcing speed limits is not among the things that I think police try at all to do. I rarely see anyone pulled over while driving, and of those, I reason, not all are for speeding; meanwhile cars fly by me constantly at 20 or more beyond the posted limit. I live in Pennsylvania and drive through the Commonwealth and near by states with some regularity.

Although I do think more should be done to both enforce speed limits and make posted speed limits more sensible/natural.

Traffic enforcement is just a state/municipality funded jobs program. On the interstate they seem to solely target speeders, while ignoring the packs of cars following <1s behind each other-- which should be easy enough to spot while stationary in the median. They also seem to selectively enforce, when they should probably be taking into consideration that a 3.5 ton lifted pickup truck with mud terrain tires going 10 over and tailgating is much more dangerous than a Toyota Camry going 10 over by itself, but you never see the pickups pulled over. In most cases, they're not making the highway safer by giving someone a ticket for going 80 in a 70 when the roads are sparsely populated. If they were actually there to promote safety, limits would be set at the 85th percentile[1] and then enforcement would be on actually dangerous driving behaviors such as tailgating, aggressive lane changes and excessively different speed vs flow of traffic.

There are places in the US with "hidden" speed cameras on interstates-- I think Sioux City, IA has them. They're marked on Google Maps & locals know to slow down near the signs that hide them, then immediately speed back up. Strangely enough, traffic doesn't accordion as much such as when an unexpected braking event happens otherwise.

[1]https://www.strongtowns.org/journal/2020/7/24/understanding-...

Magic. Got it.

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_Un...

[2] https://en.wikipedia.org/wiki/TV_detector_van

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.

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

That's hardly relevant today, of course.

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.

They're not legally allowed to enter your home without your consent, anyway.

Legally that may be the case but it seems - if the videos on the Crimebodge channel[1] are anything to go by - that they are forcing their way in, often with the help of the police.

[1] https://www.youtube.com/channel/UCUSL8poMxM_uXWzWExJaY-w

Edit: It appears that large chunks of Crimebodge's channel is private now because Youtube were threatening to delete his channel (or something, I'm not clear as to what's happened since the last time I looked) but those BBC licence fee vids don't seem to be up. I hope he gets things sorted, sorry to have wasted anyone's time with that link.

In reality it was mostly just a stunt to scare people into paying the fees. In 90s a number of countries in Europe had tried the similar actions, I remember in Serbia the national tv station RTS was advertising continuously how their technicians are walking the city with "Swedish detectors", which were some mysterious boxes, probably some kind of EM detectors, that supposedly could detect TV devices inside the homes - but of course the whole thing was a load of crap as it's a way too much work to make it profitable, so it was mainly used just to scare the senior population into paying them.

Later they simply changed the laws to make it mandatory for every household to pay the TV tax, as their detectors obviously didn't work.

Approximately every house has an aerial, its presence is not a good indicator of if there’s a TV hooked up to it. I think most likely they just look through your window.

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

"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.

> Under Section 5(1)(b) of the WT Act 1949 it is an offence if a person "otherwise than under the authority of a designated person, either:(i) uses any wireless telegraphy apparatus with intent to obtain information as to the contents, sender or addressee of any message whether sent by means of wireless telegraphy or not, of which neither the person using the apparatus nor a person on whose behalf he is acting is an intended recipient;

So yes, use of radio receivers to listen to anything in the UK, other than general broadcast or frequencies you're specifically licenced to listen to is an offence without express permission. I believe it's the main reason you can't stream Air Traffic Control frequencies in the UK, where as their available for other countries.

More information available here: http://www.monitoringtimes.com/html/mtlaws_may04.html

You don't necessarily need a radio at all to tune into WWV/WWVH -- you can listen on a telephone. (Nevermind that most telephones today use radio waves.)

(303) 499-7111 for WWV (Colorado)

(808) 335-4363 for WWVH (Hawaii)

https://www.nist.gov/time-distribution/radio-station-wwv/tel...

This would, however, void the entire purpose of this experiment.

Also it greatly reduces the value of the time signal. Over the PSTN it's usually a couple hundred milliseconds off.

WWV also transmits on 25 MHz. This is an experimental transmitter that's not mentioned in the broadcast at minute 0.

WWVH does not transmit on 20 MHz.

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