For the makers here, you can purchase cheap small modules that interface to any microcontroller, including most popular ones like AVR (Arduino), ESP32, etc. so that they can receive and decode time signals from WWVB or the European equivalent DCF77. Just search for "WWVB (or DCF77) module" at the usual online shops.
60 kHz (2022)
91–100 of 161 posts
Re: 60 kHz (2022)
#92Earlier quoted context omitted.
This is pretty much what audio compression, like a MP3 file, does: it figures out how to encode perceptually-identical (or close) stuff more densely and remove redundant information. Every time you listen to "HD Radio" you're doing exactly this.
Yes, but modern ML techniques (particularly with neural networks) are much more impressive at recovering signal with even less information than things like MP3. An example of this in the visual domain is upscaling. So it’s not a bad question at all.
Sure-- as we've discussed endlessly here: compression and ML are really very close cousins. I never said it was a bad question.
Re: 60 kHz (2022)
#93Earlier quoted context omitted.
If we could have have 58 kHz to 62, that's 4 kHz. Enough for a 300 baud modem to work, which is 300 times faster than 1 bit per second.
We need to know the signal to noise ratio. Not just the bandwidth. 4khz is enough to carry much higher rates on residential phone lines...
Alternatively, it would be fun to see how much noise you can put into the signal and still decode it. Maybe using the knowledge of its structure, kind of how (I believe?) GPS reception works.
Re: 60 kHz (2022)
#94Earlier quoted context omitted.
I guess my usual experience is that AM transmissions sound pretty horrible, especially compared to FM So, my question is more like, can we just upgrade the equipment and keep the channels? And can AM be used more like for signal/indexing rather than full data dump? (eg. instead of transmitting the whole song, transmitting just an id of the song)
The limit is Shannon's law which depends on bandwidth and signal to noise. A more advanced modulation technique can get more "information" through up to that limit. A song for this matter can just be considered information as well. So the answer is almost certainly yes, one can get more out of existing channels by upgrading the equipment assuming the current equipment doesn't approach the theoretical limit which is a…
> An FM radio channel has a bandwidth of 200Khz.
How gratuitous with modern tech. FM needs tens of decibels of signal to noise ratio to sound reasonable, especially if you want stereo. But a digital signal could fit perfect audio into that range at less than one bit per Hz, which would let it tolerate radio noise that's as strong as the actual signal.
Re: 60 kHz (2022)
#95Earlier quoted context omitted.
US seems to be the first to pioneer this according to my very cursory research: https://timeandnavigation.si.edu/multimedia-asset/us-navy-wi...
I stand corrected, it seems to indeed have been the US Navy that pioneered time signals. France followed up a few years later. I don’t know who had the first system accessible to civilians, but at this point we’d just be arguing details.
From the link:
> Radio time signals for setting chronometers were sent from stations such as NAA in Arlington, Virginia, which began broadcasting in 1913. The time was supplied from a direct communication line with the clocks of the U.S. Naval Observatory in Washington, D.C. In combination with another low-frequency installation mounted on the Eiffel Tower in Paris, the towers had the range to cover the North Atlantic Ocean and the eastern United States.
So I looked up the Eiffel tower.
> The Eiffel Tower time signal broadcasts began on May 23, 1910
https://tf.nist.gov/general/pdf/2131.pdf
Also, same source starts with the 1898 proposal of time sync via radio being made by an Irish bloke.
> I don’t know who had the first system accessible to civilians, but at this point we’d just be arguing details.
Agreed. Even non-civilian, and whoever came first, the timeline of things across various countries, I don't think the core point of TFA holds water: it's not a "particularly American" thing, it just made sense out of engineering requirements: time sync was transmitted over telegraph wires, and telegraph went wireless; the leap is not exactly surprising.
Re: 60 kHz (2022)
#96Earlier quoted context omitted.
The signal is not 60 kHz wide. It is at 60 kHz. A pure carrier with no modulation has the inverse of infinite bandwidth. (Assuming perfect transmitters, which can't really exist, of course.) The faster you modulate the signal, the more it spreads out across the spectrum. The frequency-time tradeoff. The time signals run at the low end of longwave. That spans from about 40 to 120 kHz or so. There is about 100 kHz of s…
The agency running the German equivalent to WWVB, DCF77, has looked into piggybacking an emergency warning signal onto unused bits of the time signal: https://www.ptb.de/cms/en/presseaktuelles/journals-magazines... These days though, a more popular idea seem to be to piggy back onto GNSS signals, which are also broadly available (no idea how well they compare in practice to low frequency time beacons), and for which…
> These days though, a more popular idea seem to be to piggy back onto GNSS signals, which are also broadly available (no idea how well they compare in practice to low frequency time beacons), and for which importantly many mobile devices already have a receiver built-in
GPS chips are very very power intensive as the compute power involved to decode a signal out of something that would normally be way below the noise threshold is still very high, despite some two decades worth of optimization. And they're pretty useless outside of direct line of sight towards the sky.
> In fact, I can't imagine many events other than weather (which is usually localized) that warrant such a low-entropy signal on a nationwide basis, and everything I can imagine has very limited actionability. ("Asteroid inbound, prepare to hide in the basement for a few thousand years"?)
It's a trigger signal for a low-power receiver that can then turn on a higher-bandwidth (and thus, higher power) device to detect what is actually going on. Say you're a country at war like Ukraine - have the "emergency bit" on nationwide during Russian air raids so that receivers can listen for area-specific signals and blare horns if affected.
No matter what, we have to prepare for war, and that includes having robust technology that is hard to take out on the sender side (which cellphone stations aren't, they're easy targets in a cyber war!) and, most importantly, can be stored in everyone's garden shed and live on a single battery for years.
Re: 60 kHz (2022)
#97> I’m not particularly patriotic, but this kind of thing feels particularly American.
Maybe that tinge of patriotism is why Americans don't even bother to see if something isn't an American invention - https://en.wikipedia.org/wiki/Time_from_NPL_(MSF) - they'll just claim it anyways since they barely read outside their borders.
Radio 4 would also like a word: https://en.wikipedia.org/wiki/Greenwich_Time_Signal
Re: 60 kHz (2022)
#98Earlier quoted context omitted.
Yes, but modern ML techniques (particularly with neural networks) are much more impressive at recovering signal with even less information than things like MP3. An example of this in the visual domain is upscaling. So it’s not a bad question at all.
Sure-- as we've discussed endlessly here: compression and ML are really very close cousins. I never said it was a bad question.
You can even win a prize for that https://en.m.wikipedia.org/wiki/Hutter_Prize.
Re: 60 kHz (2022)
#9960 kHz is “long wave”, a frequency so low you could almost still hear. It's just thrice the upper limit of ~20 kHz for the human ear. I love how my wristwatch eats sunlight at day (solar-powered) and drinks radio waves at night. Never has to change a battery and shows time as accurately as any internet-connected device that listens to NTP.
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Re: 60 kHz (2022)
#100> I’m not particularly patriotic, but this kind of thing feels particularly American. Maybe that tinge of patriotism is why Americans don't even bother to see if something isn't an American invention - https://en.wikipedia.org/wiki/Time_from_NPL_(MSF) - they'll just claim it anyways since they barely read outside their borders. Radio 4 would also like a word: https://en.wikipedia.org/wiki/Greenwich_Time_Signal
The US Bill of Rights is copied almost word-for-word from English legislation: https://en.wikipedia.org/wiki/Bill_of_Rights_1689