7 ms·

the bandwidth is just enough to broadcast a single digit of binary every second. I'd be interested in some more context on this. I think it's pretty clear that

the bandwidth is just enough to broadcast a single digit of binary every second. I'd be interested in some more context on this. I think it's pretty clear that you can encode more than 1bps in a 60kHz signal, but I'm curious how the encoding was chosen. There's some more detail on it here: https://en.wikipedia.org/wiki/WWVB#Modulation_format https://en.wikipedia.org/wiki/WWVB#Modulation_format The WWVB 60 kHz carrier, which has a normal ERP of 70 kW, is reduced in power at the start of each UTC second by 17 dB (to 1.4 kW ERP). It is restored to full power some time during the second. The duration of the reduced power encodes one of three symbols: If power is reduced for one-fifth of a second (0.2 s), this is a data bit with value zero. If power is reduced for one-half of a second (0.5 s), this is a data bit with value one. If power is reduced for four-fifths of a second (0.8 s), this is a special non-data "mark", used for framing. This is apparently the IRIG H encoding, which dates to the 50s and is probably designed to be easily decoded. By what, I wonder?

mmastrac 2y ago
> By what, I wonder? At that length of symbol encoding, by hand. :)
anyfoo 2y ago
Relays maybe? EDIT: Not sure why I was downvoted. Relays seem like period-accurate technology (happy to be corrected), and they’re comparably slow.
- Dylan16807 2y ago
  I can't say why you were downvoted but that's still pretty slow for relays. One bit per second seems more like it's aimed at casual human decoding. Especially because each digit is encoded separately, even for the hours. Also for plain old range purposes, one transmission per minute is about as wide as you can go before things get silly.
retrac 2y ago
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 spectrum down there. Though broadcasting a broadband longwave signal like that would be an imposing task. To cover a large area with AM broadcast (maybe 5 - 10 kHz) uses 1 - 2 megawatt transmitters in Europe. To cover the continent with a 100 kHz broadband digital signal would probably take 10 - 50 megawatts, maybe with 3 transmitter sites. Though I think it could be done. Could fit maybe a megabit a sec in there. Something less ambitious maybe. A few hundred bytes a second? A kilohertz or so of spectrum used. It could work inside elevators, deep underground in parking garages, and so on. Digital alert stream for emergencies, time signal, etc.? Would not be much more complicated than the time signal transmitters, just with a more sophisticated modulation.
- wglb 2y ago
  There is also an antenna issue with regards to resonance. If the signal spreads to wide, the antenna and associated tuning equipment are going to suffer RF losses, reflections and likely heating. That is why the 17khz naval CW station has a limitation on cw speed.
- lxgr 2y ago
  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/ptb-news/ptb-news-ausgaben/archivederptb-news/news04-2/dcf77-suitable-for-public-warnings.html 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 importantly many mobile devices already have a receiver built-in: https://defence-industry-space.ec.europa.eu/galileo-emergency-warning-satellite-service-underway-2024-01-24_en https://defence-industry-space.ec.europa.eu/galileo-emergenc... The US also already has pretty good coverage with the NOAA weather radio system, which supports a digital, zone-based alerting system for both weather and other hazards. That has the big advantage of being regionally steerable. 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"?)
wglb 2y ago
By "atomic" clocks (for example https://www.amazon.com/Crosse-Technology-WT-3129B-Atomic-Analog/dp/B0080JIVMW/ref=sr_1_7 https://www.amazon.com/Crosse-Technology-WT-3129B-Atomic-Ana...), and older brands of watches. I think there are also older industrial applications using this technology to syncronize.
- anaidioschrono 2y ago
  I love these clocks! I've had a few in every house I've lived in, from all along the West Coast and Midwest.
  - lxgr 2y ago
    Since the equivalent European signal I'm familiar with only covers a single timezone, with unified DST rules, I'm curious: Do these usually have an adjustment button for a time zone offset? And how do they handle DST – do they have an "I'm in Arizona (but not in the Navajo Nation), leave me on standard time" switch?
    - V99 2y ago
      They usually have an offset and a DST option. So in Arizona you'd choose -7/Off, and never touch it again. In Colorado you'll have to toggle DST twice a year manually, because it doesn't know the rules for when it starts/ends.
      - lxgr 2y ago
        Oh, is there no “DST in effect” flag in the signal? As I understand it, the US switches at the same day across the country (for the states that do have it), so that should theoretically be possible.
        deleted 2y ago
        [deleted]
        quintushoratius 2y ago
russdill 2y ago
Reminds me of encodings for IR remote controls such as RC5
throwing_away 2y ago
> This is apparently the IRIG H encoding, which dates to the 50s and is probably designed to be easily decoded. By what, I wonder? Wonder no more! This technology is used in wall clocks, weather stations, and even wrist-watches. They're usually marketed as "atomic clocks".
esaym 2y ago
For those of us that are visual or audio learners: https://www.youtube.com/watch?v=V0CWj9DwRBY https://www.youtube.com/watch?v=V0CWj9DwRBY
- esaym 2y ago
  And a "coverage map" https://www.nist.gov/pml/time-and-frequency-division/time-distribution/radio-station-wwvb/help-wwvb-radio-controlled https://www.nist.gov/pml/time-and-frequency-division/time-di...
zh3 2y ago
In fact there are lower-frequency signals that carry more data, generally used for submarine communication - the wikipedia article says "uo tp 300bps" using VLF (30KHz or so). Fun fact: sound cards in PC's are now fast enough that it's possible to receive many of these signals (including WWWV, DCF77 and MSF) directly with a sound card - basically connect a long wire (or tuned circuir) to the sound card input and do a bit of DSP. Sampling at 192KHz makes reception of any of these easy. [0] https://en.wikipedia.org/wiki/Communication_with_submarines https://en.wikipedia.org/wiki/Communication_with_submarines

mmastrac 2y ago

> By what, I wonder? At that length of symbol encoding, by hand. :)

anyfoo 2y ago

Relays maybe? EDIT: Not sure why I was downvoted. Relays seem like period-accurate technology (happy to be corrected), and they’re comparably slow.

Dylan16807 2y ago
I can't say why you were downvoted but that's still pretty slow for relays. One bit per second seems more like it's aimed at casual human decoding. Especially because each digit is encoded separately, even for the hours. Also for plain old range purposes, one transmission per minute is about as wide as you can go before things get silly.

retrac 2y ago

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 spectrum down there. Though broadcasting a broadband longwave signal like that would be an imposing task. To cover a large area with AM broadcast (maybe 5 - 10 kHz) uses 1 - 2 megawatt transmitters in Europe. To cover the continent with a 100 kHz broadband digital signal would probably take 10 - 50 megawatts, maybe with 3 transmitter sites. Though I think it could be done. Could fit maybe a megabit a sec in there. Something less ambitious maybe. A few hundred bytes a second? A kilohertz or so of spectrum used. It could work inside elevators, deep underground in parking garages, and so on. Digital alert stream for emergencies, time signal, etc.? Would not be much more complicated than the time signal transmitters, just with a more sophisticated modulation.

wglb 2y ago
There is also an antenna issue with regards to resonance. If the signal spreads to wide, the antenna and associated tuning equipment are going to suffer RF losses, reflections and likely heating. That is why the 17khz naval CW station has a limitation on cw speed.
lxgr 2y ago
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/ptb-news/ptb-news-ausgaben/archivederptb-news/news04-2/dcf77-suitable-for-public-warnings.html 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 importantly many mobile devices already have a receiver built-in: https://defence-industry-space.ec.europa.eu/galileo-emergency-warning-satellite-service-underway-2024-01-24_en https://defence-industry-space.ec.europa.eu/galileo-emergenc... The US also already has pretty good coverage with the NOAA weather radio system, which supports a digital, zone-based alerting system for both weather and other hazards. That has the big advantage of being regionally steerable. 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"?)

wglb 2y ago

By "atomic" clocks (for example https://www.amazon.com/Crosse-Technology-WT-3129B-Atomic-Analog/dp/B0080JIVMW/ref=sr_1_7 https://www.amazon.com/Crosse-Technology-WT-3129B-Atomic-Ana...), and older brands of watches. I think there are also older industrial applications using this technology to syncronize.

anaidioschrono 2y ago
I love these clocks! I've had a few in every house I've lived in, from all along the West Coast and Midwest.
- lxgr 2y ago
  Since the equivalent European signal I'm familiar with only covers a single timezone, with unified DST rules, I'm curious: Do these usually have an adjustment button for a time zone offset? And how do they handle DST – do they have an "I'm in Arizona (but not in the Navajo Nation), leave me on standard time" switch?
  - V99 2y ago
    They usually have an offset and a DST option. So in Arizona you'd choose -7/Off, and never touch it again. In Colorado you'll have to toggle DST twice a year manually, because it doesn't know the rules for when it starts/ends.
    - lxgr 2y ago
      Oh, is there no “DST in effect” flag in the signal? As I understand it, the US switches at the same day across the country (for the states that do have it), so that should theoretically be possible.
      - deleted 2y ago
        [deleted]
      - quintushoratius 2y ago

russdill 2y ago

Reminds me of encodings for IR remote controls such as RC5

throwing_away 2y ago

> This is apparently the IRIG H encoding, which dates to the 50s and is probably designed to be easily decoded. By what, I wonder? Wonder no more! This technology is used in wall clocks, weather stations, and even wrist-watches. They're usually marketed as "atomic clocks".

esaym 2y ago

For those of us that are visual or audio learners: https://www.youtube.com/watch?v=V0CWj9DwRBY https://www.youtube.com/watch?v=V0CWj9DwRBY

esaym 2y ago
And a "coverage map" https://www.nist.gov/pml/time-and-frequency-division/time-distribution/radio-station-wwvb/help-wwvb-radio-controlled https://www.nist.gov/pml/time-and-frequency-division/time-di...

zh3 2y ago

In fact there are lower-frequency signals that carry more data, generally used for submarine communication - the wikipedia article says "uo tp 300bps" using VLF (30KHz or so). Fun fact: sound cards in PC's are now fast enough that it's possible to receive many of these signals (including WWWV, DCF77 and MSF) directly with a sound card - basically connect a long wire (or tuned circuir) to the sound card input and do a bit of DSP. Sampling at 192KHz makes reception of any of these easy. [0] https://en.wikipedia.org/wiki/Communication_with_submarines https://en.wikipedia.org/wiki/Communication_with_submarines