WWVB broadcasts around the world on a low frequency of 60kHz with a power level of 70 kW. The question is, how does a little clock or cell phone receive this signal with a very small antenna? The wavelength is about
16,000 feet. Is this band a very low noise band where a very tiny signal can be amplified without the noise being a problem?.
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The little clocks and cell phones don't receive at that particular frequenc y.
It's used to synchronise higher frequency transmissions which they can rece ive at regular radio frequencies for the clocks (which presumably use ferri te rod antennas)and at GHz frequencies for cell-phones (which depends on sm all cells which use a limited range of different frequencies, with the cell s handing off from one cell - and frequency - to the next as you walk from cell to cell).
-- Bill Sloman, Sydney
The little clocks and cell phones don't receive at that particular frequency.
It's used to synchronise higher frequency transmissions which they can receive at regular radio frequencies for the clocks (which presumably use ferrite rod antennas)and at GHz frequencies for cell-phones (which depends on small cells which use a limited range of different frequencies, with the cells handing off from one cell - and frequency - to the next as you walk from cell to cell).
-- Bill Sloman, Sydney ---------------------------------- Bullshit. What, didn't go to Google before bloviating?
"In 2011, NIST estimated the number of radio clocks and wristwatches equipped with a WWVB receiver at over 50 million"
I'd expect them to use a resonant loop or rod antenna, detecting the h-field.
It's weird that WWVB is still on the air, what with GPS.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Not sure where you get this. Radio Controlled Clocks (RCC), which are often labeled "Atomic Clocks" because WWVB uses atomic clocks as references, directly receive the 60 kHz signal from WWVB in the US, JJY in Japan and MSF in the UK or 66.66 kHz from RBU in Russia or 68.5 kHz from BPC in China or 75 kHz from HBG in Switzerland or 77.5 kHz from DCF77 in Germany and BSF in Taiwan. There are others as well. This is well documented. There are many web pages explaining how to construct such receivers.
The US signal from WWVB is *not* heard around the world. It covers most of the US 48 states during the day and does a better job at night where it covers most of North and Central America.
The main limitation in receiving the signal is not the receiver sensitivity because the environmental noise at these frequencies is very high. Boost the signal with a better antenna and you also boost the noise. A small loop antenna works ok because it is tuned to resonance by a capacitor to peak the signal response (while reducing out of band noise), then highly amplified.
In contrast, at higher frequencies it is important to maximize the signal from the antenna as much as possible since the receiver input noise level is usually the limitation to receiver sensitivity. So a lot of work goes into the front end of HF receivers to reduce the noise level. This is not at all useful at the frequencies used for radio controlled clocks.
-- Rick
Radio controlled clocks (RCC) can be built with under $5 worth of electronics (likely much less) while a GPS module and antenna are much more expensive and use *hugely* more power. There are RCC wristwatches! Try getting GPS to work on your wrist. Just the antenna is the size of a wrist watch.
The main advantage of GPS is that it can be used over most of the populated world at any time while RCC transmissions are not available everywhere or all day as the signal propagation is much better at night. Even GPS doesn't have 100% coverage due to terrain limitations at times. I don't know if it is still a problem, but earlier on when I was more involved with GPS, the "urban canyon" was a real problem and it could be hard to tell even what block you were on because of the multi-path of the various satellites. I think better receiver design and more satellites have helped this a lot.
-- Rick
I should have remembered that the radio clock we had in the UK and the Netherlands picked up the roughly 60kHz signal directly.
Cell phones don't, so that part isn't bullshit, and you look at least as stupid in consequence.
Should have done, shouldn't I ... There's nothing more like to trap you into idiocy than a badly posed question.
-- Bill Sloman, Sydney
The LF and VLF bands are extremely noisy due to atmospherics and manmade (think smpus) sources but propagate very long distances by surface wave.
Receivers typically use a small ferrite rod loopstick antenna - in the case of wristwatches this is tiny. The very narrow bandwidth and distinctive modulation help the receiver but many timepieces will spend most of the time running from a local quartz crystal because the signal is swamped by noise. They only need an occasional sniff of the signal in breaks in the noise to make corrections.
I am not aware of cell-phones using WWv/DCF/MSF etc - I think they get time from the network.
piglet
** Coverage is not nearly that great - continental USA is about it.
** The very low frequency means the signal travels via ground wave, which gives over the horizon reception and low losses. But the main trick is the slow data rate requiring only a very narrow bandwidth combined with minimal s/n ratio required for detection of the data.
Works rather like Morse code to get through with power levels and under conditions when nothing else will.
.... Phil
I have a Garmin Foretrex 201 which straps to my wrist. It is about 3" x
1.5". It works beautifully. I used it to record my path through the jungles of Belize searching for caves. The battery charge easily lasts all day.
I have a cell phone. It seems to display the time and date pretty well. Wristwatches are mostly jewelry, and I don't wear jewelry.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
And what did that have to do with the thread?
I've worn a wristwatch since I went to secondary school, and I use it to ch eck the time - it's quicker to read it than to fish out my cell-phone.
As jewellery, it doesn't rate - the one I'm wearing now I bought in the mid
-1980's and it's Casio with a liquid crystal display. I had a programmable Sieko that I bought a bit later, which was handy, but the case lost a small but critical bit of plastic around 2000, and Sieko had given up making the watch by then, which made it irreparable.
I can't say I was ever tempted by the radio watches - the nice thing about the Casio is that the batteries last for about seven years - the Sieko was greedier - and anything with a radio in it isn't going to last that long.
I suppose to a narcissist, a wristwatch has to be jewelry, rather than devi ce to keep track of the time, but most people can separate the functions.
-- Bill Sloman, Sydney
Although it's theoretically possible to cram a ferrite antenna into a cell phone it seems most unlikely. :o)
-- Don Kuenz KB7RPU
Den 18/04/2016 kl. 05.06 skrev Bill Bowden:
Some time ago I tried to make a radio clock chip market survey to find the "best" current radio clock chip and found:
CME8000 (multi-modus receiver: WWVB, DCF77, JJY, MSF and HBG with three crystals) very low power consumption while receiving (excluding external MCU). The channel width is only 10Hz:
Digikey has complete multi-modus modules (WWVB, DCF77, JJY, MSF and HBG):
561-1005-ND (none now) Datasheet:I have no idea if this is a problem for CME8000:
That was in late 2012 that WWVB added phase modulation and broke many WWVB receivers. If that's your problem, there are a few fixes, but I suspect they're only useful for higher end receivers.
2012 WWVB Receiver Modification Modification makes receiver insensitive to WWVB's new biphase-shifted time code.Glenn
The smallest ferrite rod loopstick antenna known to me measures about
60mm in length. Yet you piglet, seem to know of even smaller antennas that fit into a wristwatch. Is it possible for you to share a part number? TIA.-- Don Kuenz KB7RPU
Ask Mr Google:
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
23.6 mm
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Thank you. Apparently ever smaller diameter wire on an ever smaller coil does the trick. OTOH a "Citizen-style" ?baroque? rod antenna seems absent from the guts of a Casio. [1] Perhaps the small circular device shown at the bottom of the picture is a SMD ferrite antenna?
All of this ferrite antenna on a wristwatch stuff (Pease parlance) seems to push the art. "Multi-antenna receiver in a radio controlled clock." [2]
Note.
-- Don Kuenz KB7RPU
Hi Don, Others have answered before me. There are even tinier ferrite loopsticks used in short range RFID tags and proximity fobs. The loopsticks used in pet animal ID tags which are injected under the skin are about the size and shape of a grain of rice!
piglet
CDMA phones certainly do -- the health and welfare of the network depends on all of the base stations being GPS-synchronized, and you can't sync up to the long code in less than a month without knowing the time -- which the base station tells you as soon as you know the short code.
I would be mildly astonished if there's any other modern cell phone protocol that does not also depend on the handset knowing the network (and hence GPS) time.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
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