[HN Gopher] 60 kHz (2022)
___________________________________________________________________
60 kHz (2022)
Author : jer0me
Score : 234 points
Date : 2024-06-01 00:05 UTC (22 hours ago)
(HTM) web link (ben.page)
(TXT) w3m dump (ben.page)
| anyfoo wrote:
| > I'm not particularly patriotic, but this kind of thing feels
| particularly American.
|
| ??? America has no doubt done some very remarkable things (the
| moon landing, the first backward compatible color TV standard),
| but I don't think this is a notable example of that.
|
| I think everyone in Europe was familiar with even wristwatches
| getting the time from "airwaves". At least in Germany, watches
| were a very common thing since the 80s (I think everyone old
| enough vividly remembers the many Junghans commercials on TV).
| The corresponding signal has been broadcast for many decades
| earlier, as it's no surprise that railroad and airplane networks
| were in need of a common time:
| https://en.wikipedia.org/wiki/DCF77
|
| > But we had a problem, and we solved it with technology. And
| none of that fancy newfangled technology -- we solved it using
| solid technology, the kind that you can touch with your hands and
| that buzzes in the airwaves.
|
| There wasn't much "newfangled technology" around at the time. We
| essentially solved it using the simplest method there was at the
| time, at least I find it a bit hard to come up with a simpler
| one.
|
| Also, what would be an example of technology that you can't
| either "touch with your hands" or that does "buzz in airwaves"?
| aeonik wrote:
| US seems to be the first to pioneer this according to my very
| cursory research: https://timeandnavigation.si.edu/multimedia-
| asset/us-navy-wi...
| anyfoo wrote:
| 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.
| lloeki wrote:
| 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.
| aeonik wrote:
| Nice find!
|
| This turns out to be quite an interesting rabbit hole.
|
| It's definitely earlier than I would have guessed
| regardless.
| Dalewyn wrote:
| >what would be an example of technology that you can't either
| "touch with your hands" or that does "buzz in airwaves"?
|
| Microprocessors and lights/lasers respectively, among I'm
| certain countless other examples.
| anyfoo wrote:
| I can touch microprocessors, and lasers are buzzing in
| airwaves. It's the same electromagnetic radiation as what we
| know as radio, just at much, much higher frequencies.
|
| But this was asked in the context of solving this problem, in
| the 1950s.
| pavel_lishin wrote:
| Sure, but trench soldiers used to build their own radios. A
| soldier today stationed in the middle of a war isn't likely
| to assemble their own laser emitter.
| anyfoo wrote:
| I don't think anybody at that time could have built a
| laser emitter, even. Not sure why you would want to, to
| solve that problem, even today.
|
| I feel like the point of my question was lost.
| Dalewyn wrote:
| >I can touch microprocessors,
|
| No you can't, you're just touching the box they come in.
|
| You can touch copper cables and wires, vacuum tubes,
| resistors, capacitors, breadboards, and (large!) printed
| circuit boards among other "basic" electronic components.
| You can't touch microprocessors, it's even stated on the
| tin they are _micro_ scopic in scale; you can't touch that
| in any meaningful way.
| anyfoo wrote:
| We could argue about that, but let me rephrase then:
|
| What technology that you can neither touch, nor that
| buzzes in airwaves, could they have used to solve this
| problem back then?
| someguydave wrote:
| Digital communications is America's gift to the world, look up
| Claude Shannon
| sokoloff wrote:
| I think the Englishman George Boole deserves significant
| credit as well.
| spixy wrote:
| AC motor, steam, diesel, jet engines are european "gifts to
| the world",
|
| yet it would be cringe to write sentence like "I'm not
| particularly patriotic, but this kind of thing feels
| particularly European"
| Aloisius wrote:
| _> I think everyone in Europe was familiar with even
| wristwatches getting the time from "airwaves". At least in
| Germany, watches were a very common thing since the 80s_
|
| Not the 80s. The first radio controlled wristwatch came out in
| 1990 (Junghans Mega 1).
| anyfoo wrote:
| Sorry, I mistranslated "clock" (hence why I differentiated
| "wristwatch" in the sentence before). We owned a Funkuhr-
| Wecker in the 80s, so, an alarm clock synchronizing to DCF77,
| in the 80s. The wristwatches came a bit later, yeah (not that
| I'd have known without looking it up whether that was earlier
| or later than 1990).
| layman51 wrote:
| I wondered about its American origins too. I vaguely remember a
| little detail in the novel Cryptonomicon where one of the
| characters (a Lieutenant in the Imperial Japanese Army during
| WWII) sets his watch with a radio time signal. So that got me
| thinking that maybe the idea arose in different places.
|
| Also I was wondering about the "forever" wording. I imagine the
| signal is very robust, but couldn't American politics just one
| day decide that it's not worth it to broadcast the time by
| radio signal anymore?
| 2four2 wrote:
| There are several of these stations, they are maintained and
| operated by NIST. Two of them were almost shut down recently due
| to budget concerns:
|
| https://www.radioworld.com/global/why-wwv-and-wwvh-still-mat...
| dfc wrote:
| In April one of the two WWVB antennas failed (broke) because of
| 90mph winds.
|
| https://www.nist.gov/pml/time-and-frequency-division/time-di...
| Eduard wrote:
| https://www.nist.gov/pml/time-and-frequency-division/time-
| di...
|
| > Official Notice: Commencing from 0000 Coordinated Universal
| Time (UTC) on April 7, 2024, the southern antenna of WWVB has
| been rendered non-operational due to damage sustained from
| wind gusts exceeding 90 MPH. Please be advised that WWVB
| continues to function at a diminished overall power,
| utilizing only its northern antenna.
|
| > Update 20 May 2024: The components necessary for the
| refurbishment of the southern antenna's triatic are currently
| being manufactured and shipped. The projected timeline for
| the completion of these repairs is tentatively set for the
| latter part of June 2024. We would like to emphasize that
| this is an estimated timeline and may be subject to
| alterations based on a variety of factors. We greatly
| appreciate your understanding and patience during this
| process.
|
| Can someone using WWVB radio clocks describe what the current
| situation is? Is the second working antenna strong enough to
| provide signals throughout the US / North America?
|
| Are WWVB radio clocks popular at all?
|
| Here in Europe, DCF77-based clocks are popular, especially
| with respect to automatic summer time adaption and (less
| obvious) leap second HANDLING. It would be very noticeable
| eventually if the DCF77 signal had severe issues.
|
| Also, I'm very surprised about the abysmal historical uptime
| of Wwvb. It lists thirteen downtimes of more than 5 minutes
| each in 2023 alone.
| lxgr wrote:
| Given that most clocks listen for it about once per day, if
| that, to save battery, and in my experience even then only
| manage to catch the signal every couple of days, high
| continuous availability doesn't really seem to be a
| concern.
| tkzed49 wrote:
| _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
|
| _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 wrote:
| > By what, I wonder?
|
| At that length of symbol encoding, by hand. :)
| anyfoo wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 importantly many mobile devices
| already have a receiver built-in:
|
| 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"?)
| morpheuskafka wrote:
| > a more popular idea seem to be to piggy back onto GNSS
| signals
|
| Don't all GNSS systems provide a highly accurate time
| signal (maybe needed for computing the distance to
| satellite)? I know GPS does at least.
| BenjiWiebe wrote:
| Yes, it is needed to compute a location. More accurate
| time = more accurate location.
| lxgr wrote:
| Yes, the GPS signal in a way _is_ primarily a very
| precise time signal :) It's a TDOA system!
|
| I was referring to piggying back an emergency signal onto
| that!
| stkdump wrote:
| As mentioned somewhere else, these time signals also
| carry information about DST and adapt for leap seconds,
| both of which GPS doesn't do as far as I know. I remember
| that earlier versions of Android always set the phone
| clock to GPS which was then off by a number of seconds.
| kqbx wrote:
| GPS navigation messages do include information about leap
| seconds and other stuff necessary to convert between GPS
| time and UTC. See GPS Interface Specification IS-GPS-200,
| 30.3.3.6.2 - UTC and GPS Time
| mschuster91 wrote:
| > 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.
| meindnoch wrote:
| >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.
|
| And what would prevent Russia from continuously
| broadcasting this emergency bit to cause chaos?
| mschuster91 wrote:
| > And what would prevent Russia from continuously
| broadcasting this emergency bit to cause chaos?
|
| So what, all that would do in my scenario is drain the
| batteries of the civilian populations' alarms a bit
| faster as they'd keep their more power-intensive CPU
| awake.
| zh3 wrote:
| DCF77 is a natural for this because it already includes a
| phase-modulated signal (as well as the 1bps amplitude-
| modulation). At the moment it's a 512-bit pseudo random
| sequence, but could obviously carry a data stream instead.
| kazinator wrote:
| 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.
| YZF wrote:
| 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...
| eternauta3k wrote:
| 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.
| YZF wrote:
| GPS is spread spectrum. It's modulated using a pseudo
| random sequence and then demodulated using the same
| sequence. All the same theory still applies but it's just
| a different way of using the spectrum, instead of a fixed
| band the bandwidth is "spread" across a broader band in a
| way that allows all these different signals to be
| multiplexed. Specifically with GPS IIRC the phase of the
| pseudo random sequence is also conveying timing
| information because of how it relates to the precise
| clock on the satellites. Spread spectrum can be a little
| more resilient to certain kinds of noise, e.g. if you
| have noise just at one frequency now you've reduced the
| impact of that noise.
| retrac wrote:
| It's fun with software radio to take a long recording of
| a chunk of spectrum and do the fourier transform and plot
| it. There will be clear lines indicating carriers, even
| ones too faint to be heard over the static. Software can
| do the same trick for decoding a modulation (at the
| expense of latency in decoding). Modern tech allows a
| further neat hack here. If you have a very stable local
| clock (which any modern digital device does) you can
| correct for frequency errors in the transmission. Once
| the clocks are synced, you know exactly when the next
| symbol should be. And you know how much the transmitter
| frequency as actually received, is varying from what it
| should be. And since a convolutional coding with a
| pseudorandom number might be used, you also know what the
| next symbol will be (only a small number are valid in any
| state). With all that together, in effect, the decoder
| knows when and where the signal will be, and at least
| part of what it will look like, before it receives it. So
| it can be compared with what is actually received, making
| it possible to pick it up well below the noise floor.
| Just add some error correcting codes for robustness.
|
| Amateurs have successfully communicated data between
| California and New Zealand on longwave using only 1 watt
| of radiated power at the transmitter. (But the baudrate
| for that is measured in hours per bit. And the receiving
| antenna was considerable.)
| nico wrote:
| Could we have something like an AM broadcast, but then the
| receiver "upsampling" the data? Maybe using some ML?
|
| For example, if you have an AM channel that always transmits
| some song from a list, then you might not even need to
| receive the whole song. Or maybe you can have a model that's
| good at upsampling those types of songs/data?
| mlyle wrote:
| 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.
| vlovich123 wrote:
| 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.
| mlyle wrote:
| Sure-- as we've discussed endlessly here: compression and
| ML are really very close cousins. I never said it was a
| bad question.
| keithalewis wrote:
| You can even win a prize for that
| https://en.m.wikipedia.org/wiki/Hutter_Prize.
| vlovich123 wrote:
| I extremely dislike the Hutter Prize. I think it's
| generally agreed that intelligence compresses the model
| better & therefore it's reasonable to assume that the
| better the compression, the more intelligence you have
| (at least for now where we are with AI, this seems to be
| a roughly reasonable assumption). My problem with the
| Hutter prize is that it makes the leap to say that
| lossless compression is this when everything about AI is
| choosing how much error you're willing to tolerate. In
| other words, intelligence is linked to _lossy_
| compression, not lossless - a competition for lossless
| compression doesn 't do anything more than get us better
| lossless compressors / decompressors.
| YZF wrote:
| AM broadcast uses a "band" around the carrier. Whatever
| tricks you use Shannon's law is going to determine the
| upper limit of how much data you can carry which depends on
| the bandwidth and the signal to noise ratio. ML makes no
| difference from a theoretical perspective. Compression just
| reduces the bandwidth you'll need assuming your data
| compresses (with whatever method you choose, ML can be part
| of that)...
| nico wrote:
| 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)
| vlovich123 wrote:
| AM sounds bad because it's amplitude modulated. So
| variation in amplitude (i.e. signal strength) results in
| noise when decoding. FM however is not sensitive to this
| issue because its frequency modulated - slight variations
| in signal strength have no effect on the encoded signal.
|
| And yes, we can always upgrade the equipment. That's what
| we did when we transitioned TV to digital signals and FM
| to digital FM - we reserved some bandwidth for over-the-
| air while freeing up the rest to be used for other
| purposes. But it's an expensive proposition and one that
| happens rarely (in fact those are the only two times I'm
| aware of it, they happened at basically the same time,
| took forever, & there was insane opposition to it).
| YZF wrote:
| 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 almost certainly the case for
| this "old" technology we're talking about.
|
| An FM radio channel has a bandwidth of 200Khz. AM radio
| has a bandwidth of of 10Khz. That's a big part of the
| reason why AM sounds horrible compared to FM. The way
| noise impacts AM and FM is also different, especially
| given human perception. IIRC both these methods were
| picked for practical reasons not necessarily any optimal
| criteria. AM is fairly crude, there's only so much you
| can change the amplitude for any practical purpose.
| Changing the frequency makes it easier to use more
| bandwidth so it was a natural evolution. Depending on how
| you're modulating the amplitude (the naive old school
| radio IIRC is just using the signal you're transmitting
| to modulate it) you can make the bandwidth larger or
| smaller. Random e.g. something like Ethernet on copper
| can be viewed as a very very fast, high bandwidth, AM.
| All these things boil down to the same Shannon law just
| with somewhat different efficiencies depending on how
| well you can control the frequency domain.
|
| This problem of cramming the most bits into a given
| channel is something people have been working on for a
| long time. Some coverage of this here:
| https://en.wikipedia.org/wiki/Modulation
|
| That's how we got from 300bps modems to 56k modems over
| the same phone lines way back and how we push more out of
| radio spectrum today.
| Dylan16807 wrote:
| > 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.
| cycomanic wrote:
| One thing you forgot to mention is that in contrast to an
| FM receiver, or even more a digital one, AM receivers are
| incredibly easy to build even with very basic "household
| items", which I believe is at least part of the
| motivation to provide emergency services and similar
| broadcasts over AM.
| wglb wrote:
| By "atomic" clocks (for example 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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.
| quintushoratius wrote:
| Not every region of the continental US respects DST.
| lxgr wrote:
| I know, but if it does, it switches on the same day as
| all the others, which could be encoded in the signal, and
| it seems like it is [1].
|
| So instead of a switch to "add an hour", there could be
| one that says "add an hour if the signal says DST is
| currently in effect".
|
| [1] https://en.wikipedia.org/wiki/WWVB#Amplitude-
| modulated_time_...
| joezydeco wrote:
| The time code format does include a DST bit.
|
| https://www.nist.gov/pml/time-and-frequency-
| division/time-di...
| o11c wrote:
| You shouldn't have to toggle DST manually; it's encoded
| at :57-58.
|
| That said, my clock stopped syncing for some reason, so
| ...
| wglb wrote:
| The one remaining clock I have took a hard fall, and no
| longer syncs.
| metaphor wrote:
| > _...and older brands of watches._
|
| Modern watches too, e.g. Casio digital watches marketed as
| integrating their "Wave Ceptor"/"Multi-Band 6" feature[1].
|
| I still use a 17-year-old (batch code[2] 202A327G) G-Shock
| GW-530A (predecessor of this active offering[3]) that syncs
| with WWVB every morning several hours before dawn.
|
| [1] https://en.wikipedia.org/wiki/Casio_Wave_Ceptor
|
| [2] https://shockbase.org/watches/batchcode.php
|
| [3]
| https://www.casio.com/us/watches/gshock/product.GW-M530A-1/
| esaym wrote:
| Wow, added to wish list!
| russdill wrote:
| Reminds me of encodings for IR remote controls such as RC5
| throwing_away wrote:
| > 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 wrote:
| For those of us that are visual or audio learners:
| https://www.youtube.com/watch?v=V0CWj9DwRBY
| esaym wrote:
| And a "coverage map" https://www.nist.gov/pml/time-and-
| frequency-division/time-di...
| zh3 wrote:
| 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
| khaki54 wrote:
| I can picture a room full of engineers in ties, wearing pocket
| protectors full of implements, chain smoking cigarettes while
| coming up with this one.
| erikpukinskis wrote:
| I can picture a black woman at a desk in a nicely pressed dress
| coming up with this one on pencil and paper.
| neilv wrote:
| https://en.wikipedia.org/wiki/Hidden_Figures
| mmastrac wrote:
| More likely a radio nerd, John Alvin Pierce, that was just
| really good at radio and obsessed with oscillators
| (https://ieeexplore.ieee.org/document/60675) that inspired a
| group of distinguished government-employed engineers and
| scientists.
|
| In fairness, there _might_ be a pocket-protector in this
| picture of them but it's a bit blurry. Actually, yes, there
| definitely is. No cigarettes, however:
|
| https://www.ncbi.nlm.nih.gov/core/lw/2.0/html/tileshop_pmc/t...
| on image to zoom&p=PMC3&id=4487279_jres.119.004f7.jpg
|
| [1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4487279/
| metaphor wrote:
| Quick image link fix...spaces in URL broke auto-hyperlinking:
|
| https://www.ncbi.nlm.nih.gov/core/lw/2.0/html/tileshop_pmc/t.
| ..
| denton-scratch wrote:
| Damn, he's got _two_ pocket protectors!
| andrewstuart wrote:
| Pretty sure there'll be lots of comments on this to do with
| bandwidth and speed of light.
| frankus wrote:
| It's kind of baffling that in 2024 there are appliances that
| exist for which I have to manually set the time, or at least have
| to go through some cumbersome IoT set-up process, that most
| likely is absolute garbage security-wise if it isn't actively
| acting against my interests (like those fridges that only work
| with first-party water filters).
|
| Maybe I'm under-thinking this, but couldn't my Wi-Fi router just
| broadcast the current time (and time zone) every minute or so in
| an unencrypted fashion to all devices within range?
| joshellington wrote:
| Yes but then that would require consensus on protocol,
| encoding/decoding, etc., aka the things large companies are the
| worst at aligning on.
| pavel_lishin wrote:
| Plus you have to defend yourself from the neighborhood kid
| who thinks that it'd be a laugh riot to randomize everyone's
| clocks at 5:15 in the morning.
| joshellington wrote:
| That would have absolutely been myself, wardriving at 16
| (back in the early aughts). Sending nonsensical print jobs
| and then setting everyone's clocks to 4:20.
| MadnessASAP wrote:
| I'm in my mid 30s and I still regularly tell unattended
| Google Homes and Alexa's to set an alarm for 4 AM.
| pavel_lishin wrote:
| I'm not that malicious, I just like picking up friends'
| unattended phones and snapping a goofy selfie for them to
| discover later.
| z3phyr wrote:
| There is only one government
| Talkative32 wrote:
| They servant bodies represent past abilities recent
| demonstrate open world
| alright2565 wrote:
| It is baffling that in 2024 that my appliances don't have a
| battery backup for the time. It costs less than 50 cents and
| requires the battery be changed no more than every 20 years.
|
| But still every time the power goes out I need to reset my
| clocks.
| lxgr wrote:
| It could - but it could just as easily (either accidentally or
| on purpose) broadcast the _wrong_ time, greatly annoying
| everybody within broadcast distance.
|
| Of course the same is also possible for WWVB, but at least
| there, I suspect that some agencies might take objection and
| convince you to stop sooner or later.
| em3rgent0rdr wrote:
| NTP (https://en.wikipedia.org/wiki/Network_Time_Protocol) can
| be run on any OpenWRT router. Too bad it isn't a standard
| feature of every router and appliance.
| denton-scratch wrote:
| > appliances that exist for which I have to manually set the
| time
|
| I've never owned an electric oven that could configure its own
| time. Anytime there's a power cut, I have to do some crazy
| dance - which usually involves digging out the oven's manual.
| It's the same for microwave ovens. I don't know why they don't
| at least store the time in a scrap of NVRAM, like a PC
| motherboard.
| ianburrell wrote:
| I have thought that Matter should have a time broadcast message
| that can be sent over Wifi, Bluetooth, and Thread. Which should
| be enough to set the time for any Wifi device that doesn't need
| NTP, and low-power devices with Bluetooth and Thread.
|
| One problem is that need to pair with Wifi, Bluetooth, and
| Thread. The other problem is the cost to add time sync. And
| probably couldn't remove the UI for setting the clock because
| need it for people without technology.
| FrustratedMonky wrote:
| ""I'm not particularly patriotic, but this kind of thing feels
| particularly American. Perhaps my imagination of American
| innovation is still set in the era of lunar missions and radio.""
|
| Yes. From the first trans continental train, telegraph, up
| through landing on the moon. It does inspire a lot of patriotism,
| it was very 'can-do' time. Very innovative, huge public works.
| The old technology is still amazing.
| wayeq wrote:
| Not to mention the voyager missions.. still zooming out into
| interstellar space..
| kristofferR wrote:
| This got me thinking of this video:
|
| https://www.youtube.com/watch?v=IbUhA6Vt6Sk
|
| "We just lost the most powerful longwave transmitter in Europe,
| and why that's kind of a big deal" (2023)
|
| Slight Technology Connection vibes, really fascinating stuff.
| lxgr wrote:
| I remember my dad getting a solar-powered wristwatch that could
| tune in to the Western European equivalent of WWVB (DCF77,
| located in Germany) and adjust itself (respecting DST!) when I
| was a teenager.
|
| Not that I'd regularly suffer from empty watch batteries or
| horribly incorrect time on my quartz watch, but I always found
| that extremely neat :)
| sllabres wrote:
| If I think about time an American nowadays the first thing that
| comes into my mind is GPS. What WWVB or DCF77 (and JJY) was back
| then is now GPS timing capabilities. Much higher precision but of
| course a higher complexity for the receiver. [1]
|
| I don't know about WWVB and JJY but the German DFC77 is not only
| AM modulated but FM too allowing for a better accuracy.
|
| [1] https://www.hopf.com/dcf77-gps_en.php#chapter3
| rkagerer wrote:
| I looked into getting a wristwatch that uses this.
| anonymousiam wrote:
| WWVB data transmission format is described here:
|
| https://www.nist.gov/system/files/documents/2017/05/09/NIST-...
| mehulashah wrote:
| Well said. Simple, solid technology for the benefit of everyone.
| pcdoodle wrote:
| Can you use this in basically the lower 48 with a long antenna?
|
| Free RTC L48?
| systemvoltage wrote:
| Slightly tangent: being substantively patriotic is cool. It
| _should_ be cool. America has done some incredible things like
| this and I'm sure it's not just Americans that find it cool.
| nocoiner wrote:
| Well said. I couldn't agree more.
|
| I think there are a lot of countries that have done some really
| remarkable things. I'm American, and I'm generally very proud
| of my country. If I were, say, French, Swedish or Japanese, I'd
| feel the same way.
|
| Obviously none of those countries - or any country - is
| perfect, and all have some distinctly dark chapters in their
| past, but there's something inspiring about a society
| organizing itself to accomplish generally good things.
| servus45678981 wrote:
| I honestly think pride only makes sense if the place feels
| more than home to you; the people always were more important
| than some man-made borders and identities.
| servus45678981 wrote:
| Blind patriotism isn't cool. Most of those inventions were
| invented by multicultural people, so it has really not so much
| to do with the country.
| vzaliva wrote:
| Decoding these signals should be a fun 1st project for Software
| Defined Radio. Google search shows several projects which did
| just that.
| kqbx wrote:
| Can confirm, it's a great way to get started with radio stuff.
| Since I live in Europe, I did this with the German DCF77
| signal. The frequency is low enough that you can do direct
| sampling with a 192ksps sound card or with an RP2040.
|
| A nice thing about DCF77 is that once you manage to receive the
| amplitude modulated signal, you can move onto decoding the
| slightly more advanced spread-spectrum phase modulated signal,
| which carries (almost) the same data.
|
| You can start by buying a time signal receiver module, and once
| you confirm that the module can receive the signal, cut off the
| ferrite antenna and use it with your own receiver.
|
| Here's a nice article on which I based my own project:
| https://hal.science/hal-02182845/
|
| Using the same setup (ferrite stick -> discrete transistor
| amplifier -> RP2040) I also managed to receive the polish AM
| station at 225kHz.
| LeoPanthera wrote:
| Sadly, WWVB is damaged. At midnight on April 7, 2024, WWVB's
| south antenna was disabled due to damage sustained during high
| winds. WWVB now broadcasts exclusively from the north antenna, at
| a reduced power of 30kW. This situation is expected to continue
| "indefinitely", presumably because of a lack of budget for
| repairs.
| jimbobimbo wrote:
| This looks like a great candidate for crowd funding.
| blt wrote:
| yes, in this case I'd say a good crowd funding platform is
| the IRS.
| michaelsshaw wrote:
| Important to note the update:
|
| Update 20 May 2024: The components necessary for the
| refurbishment of the southern antenna's triatic are currently
| being manufactured and shipped. The projected timeline for the
| completion of these repairs is tentatively set for the latter
| part of June 2024. We would like to emphasize that this is an
| estimated timeline and may be subject to alterations based on a
| variety of factors. We greatly appreciate your understanding
| and patience during this process.
| anArbitraryOne wrote:
| I like the topic very much, but why did this very basic blog post
| get so many upvotes?
| nicbou wrote:
| It introduces something new that tickles our curiosity. Not
| everything needs to be a long read. I do like short posts.
| bb88 wrote:
| For those looking to hear what this sounds like without buying
| any radio gear, there are many public kiwisdr sites that can hear
| 60khz. It's a matter of choosing AM decoding and tuning to the
| particular frequency.
|
| http://kiwisdr.com/public/
|
| Many of these have user limits and time limits as well. Note that
| you can also hear WWVB on 2.5mhz, 5mhz, 10mhz, and 15mhz.
| misstuned wrote:
| You can also pick "timecode" from the extensions menu in the
| KiwiSDR interface and actually decode the time signal live on
| the receiver.
| mikewarot wrote:
| I have a friend with a 300' longwire antenna. A few weeks ago,
| after we were done repairing an old receiver that included VLF,
| he tuned in WWVB for me... checking it off my bucket list. It was
| interesting to hear the beeps of different lengths.
|
| It came in surprisingly clear, in our Chicago suburb, especially
| since this was after the antenna issue on their end.
| asix66 wrote:
| I wear a Citizen "AT" [1] wristwatch daily. It not only keeps
| perfect time, because of its daily sync at 2am to WWVB, but it
| also never needs a battery change since it self charges from
| light. These two features make it the perfect zero maintenance
| timepiece IMHO, and it looks stylish too.
|
| [1] https://www.citizenwatch.com/us/en/collection/mens-atomic-
| ti...
| mlindner wrote:
| This is completely incorrect. Time synchronization across the
| entire US is done via GPS, not radio signals.
| tempodox wrote:
| 60 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.
| squarefoot wrote:
| 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.
| tanepiper wrote:
| > 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
| cjs_ac wrote:
| The US Bill of Rights is copied almost word-for-word from
| English legislation:
| https://en.wikipedia.org/wiki/Bill_of_Rights_1689
| mixmastamyk wrote:
| A copy of the Magna Carta was in the National Archives for a
| while, and John Locke was a notable influence on founders
| such as Jefferson. _Nihil novi sub sole._
| pohl wrote:
| I saw it there the day before yesterday!
| mixmastamyk wrote:
| Cool--I saw it once, and then it was gone a few years
| later. Maybe being serviced.
| CPLX wrote:
| In fairness, the United States is a breakaway region of Great
| Britain.
| yatopifo wrote:
| Afaik, not Great Britain which is Scotland, Wales and
| England combined. It was part of the British Empire when it
| broke away.
| cjensen wrote:
| Inspired by, certainly. The founders were not ignorant and
| were aware of precedent.
|
| But calling it "almost copied word-for-word" is not
| justifiable. On a trivial basis, it's literally not word-for-
| word in any way. On a more serious basis, there are
| significant changes in the laws, and enshrining something in
| an Act which can be changed by future Parliaments is a lot
| different that enshrining something into a Constitution which
| is much harder to change.
| new299 wrote:
| WWVB also broadcasts on 60KHz and a number of other
| frequencies. WWV (time signal on different frequency) was
| started a few years before the one you mention. Though I'm not
| sure it's really worth arguing about... not sure who was the
| first radio time signal.
|
| https://en.m.wikipedia.org/wiki/Radio_clock
| zh3 wrote:
| Radio 4 is particularly interesting, as it carries additional
| 25bps data [0] using for radio teleswitch operation [1] - a
| service whose days are numbered. Quite fun to receive this
| signal, as it's trivial to build a 198KHz receiver and to
| recover the data stream (+ time signal) using a signal, e.g.
| mix it with a 200KHz signal and process the resultant 2Khz
| audio tone.
|
| [0] https://www.bbc.co.uk/rd/publications/rdreport_1984_19
|
| [1] https://en.wikipedia.org/wiki/Radio_teleswitch
| tanepiper wrote:
| Radio 4 is also the station that if there is no communication
| with mainland UK, and Radio 4 no longer broadcasting,
| submarine commanders were to assume the country was attacked
| and destroyed.
|
| https://en.m.wikipedia.org/wiki/Letters_of_last_resort
| nabla9 wrote:
| Existed everywhere in the world since radios became common.
|
| I have an old solar powered Casio g-shock multi-band watch and
| it gets signals from transmitters located in US, Germany, UK,
| 2X Japan and China. I have never needed to put watch on time,
| or change batteries.
| https://gshock.casio.com/intl/technology/radio/
| lxgr wrote:
| These are indeed very cool!
|
| If for some reason you are a few standard deviations more
| paranoid about not having the correct time than the average
| person, they now apparently have models that can get the
| current time via GPS, time beacon, _or_ Bluetooth from a
| connected smartphone :)
|
| https://gshock.casio.com/us/technology/3way/
| tompccs wrote:
| NPL - the National Physics Laboratory in Teddington, London,
| also invented packet switching, the foundational technology for
| the internet.
|
| https://en.wikipedia.org/wiki/Packet_switching
| ToValueFunfetti wrote:
| >The first radio time signal, sent by telegraphic code, was
| broadcast in September 1903 by the United States Navy. Most
| sources list Navesink, New Jersey as the site of this
| broadcast, but the reference clock was located at the United
| States Naval Observatory (USNO) in Washington, DC. The first
| regularly scheduled time broadcasts began on August 9, 1904*
| from the Navy Yard in Boston. By the end of 1905, the Navy had
| transmitted time signals from stations in several other cities,
| including Norfolk, Newport, Cape Cod, Key West, Portsmouth, and
| Mare Island in California
|
| (PDF) https://tf.nist.gov/general/pdf/2131.pdf
|
| *Another source said August 9, 1905
| tanepiper wrote:
| Yes but it's not "particularly American".
|
| "In November 1898, an optical instrument maker and inventor
| named Sir Howard Grubb addressed the Royal Dublin Society and
| proposed the concept of a radio controlled clock."
|
| It was already used in telegraph transmission.
|
| America just implemented first.
| zaxomi wrote:
| And before radio, between 1880-1927, time was pumped
| throughout Paris in the form of compressed air using a
| network of pneumatic tubes.
| asddubs wrote:
| inventing a solution to a problem, only in america
| benhurmarcel wrote:
| It's like apple pie then
| dusted wrote:
| I was going to remark on this as well, but my observation is
| different: It strikes me as a very (old-school) American thing
| indeed. But not a modern American thing, if it was a modern
| American thing, it'd be privately owned, for profit with
| continually degrading quality and multiple incompatible
| "service providers" competing to trick people into their
| particular walled garden..
| dinoqqq wrote:
| American patriotism set aside, I share the author's enthusiasm
| for these types of technology! The post's main focus on how we
| stand on the shoulders of giants is so true! It makes me happy
| and proud as well.
|
| Another fascinating technology that we take for granted, is the
| possibility to travel with 280km/h in a train and still be able
| to receive digital bits and bytes. What kind of witchcraft would
| our grand-grand-grandparents have called that?
| barrenko wrote:
| Wonderful post, thank you.
| jgrahamc wrote:
| The WWVB transmitter sometimes has surprisingly long propagation:
| https://blog.jgc.org/2021/07/receiving-wwvb-time-signal-in-p...
| and https://blog.jgc.org/2023/03/wave-ok-wwvb-time-signal-
| sets-m...
| belter wrote:
| If you go below 300 Hz, you are probably into some hardcore top
| secret stuff:
| https://en.wikipedia.org/wiki/Communication_with_submarines
|
| Assuming salt water, a 1024 Kb message should take around 3 hours
| to transmit.
| evanjrowley wrote:
| Earlier this week I purchased a Casio Waveceptor watch. It
| features the ability to synchronize with this radio signal. I'm
| very happy with it. I was also happy with an early-2000s model
| for several years prior. The older one's receiver seemed to
| become unreliable after about a decade, possibly due to changes
| in the wireless spectrum over time. Overall, it was quite a
| reliable watch and so I have good confidence in this product
| line.
| kwhitefoot wrote:
| 1 bps on a 60 kHz carrier? That is certainly not the maximum
| possible data rate.
|
| There are AM stations broadcasting at only two or three times
| that frequency that broadcast voice and music.
|
| Perhaps they meant that it is the most practical for small
| receivers like watches.
|
| BBC R4 Longwave is at 198 kHz (formerly 200 kHz). The transmitter
| at Droitwich has been broadcasting voice and music since 1934.
| esaym wrote:
| I see there are cheap indoor wall clocks that are syncd with
| WWVB. But can't find anything that use gps instead. I am
| wondering why? Are the receivers too power hungry or the signals
| just too weak? I'd think going with a gps time sync would be a
| more future proof design.
| Liftyee wrote:
| Could someone please explain why the low frequency means the
| bandwidth is limited to 1 bps? Why can't the signal be turned on
| and off more times per second to transmit at a higher rate?
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