In article <(E-Mail Removed). com>,
Radium <(E-Mail Removed)> wrote:
>> Going to the source:
>> <http://tf.nist.gov/stations/radioclocks.htm>
>> NIST Recommended Practices for WWVB receivers.
>> <http://tf.nist.gov/general/pdf/1976.pdf> (See section 8A)
>> "We recommend that RCC products should be sensitive enough
>> to successfully synchronize to signals from WWVB with a field
>> strength of 50 uV/m, if the signal to noise ratio exceeds 20 dB.
>> The RF bandwidth of the receiver should be narrow, typically
>> =B110 Hz or less."
>> and:
>> "Wristwatch antennas should not be contained in the band,
>> so that RCC watch bands can be replaced in the same manner
>> as the bands of ordinary watches when they are damaged or
>> worn out."
>>
>> So much for the antenna in the wrist band idea. So, the question is,
>> what type of tiny antenna will work with such a field strength at
>> 60KHz. I dug through the FCC ID web pile looking for an inside photo
>> of Casio watch, but couldn't find anything. I'm gonna have to either
>> break one open, and/or calculate the field strength of a very small
>> ferrite rod antenna (later).
>>
>> --
>> Jeff Liebermann j...@cruzio.com
>> 150 Felker St #D http://www.LearnByDestroying.com
>> Santa Cruz CA 95060http://802.11junk.com
>> Skype: JeffLiebermann AE6KS 831-336-2558
>
>Sorry, I am now extremely interested and frustrated about how the
>wristwatch can be so tiny yet receive so long-wave signals.
>
>Just how does such a magical device work? It seems to defy laws of
>science that such a small device can operate at such long-wavelengths
>of radio waves.
>
>I suspect it's probably something those FBI/CIA bastards are going to
>keep secret from us.... >>SNIP<<
$DEITY, man, get a grip on yourself, OK? This is *old* technology - a
similar method has been used in AM radios for decades, dating to back
before the transistor was invented. There is nothing at all tricky,
or hidden/concealed about it.
>No offense but please respond with reasonable answers & keep out the
>jokes, off-topic nonsense, taunts, insults, and trivializations. I am
>really interested in this.
So, go "back to the source" just as the previous poster did.
A quick Google on the phrase "wwv watch antenna ferrite" turns up, as
its very first alternative, the following:
http://tf.nist.gov/general/pdf/1877.pdf
which is a very nice overview of radio controlled clocks, courtesy of
the United States Government (specifically, the National Institute of
Standards and Technology).
On Page 11 you'll see a clear photo of the sort of antenna used in a
WWVB-capable desk clock. It's a standard ferrite loop antenna.
On the following page you'll see a photo of the innards of a
WWVB-capable watch. It has a similar (although smaller)
ferrite-loaded loop antenna.
If you go to
http://www.mas-oy.com/data/MAS_docu_AR.htm you'll find
the web site (with data sheets) for WWVB receiver chips. Download the
MAS9180 data sheet. You'll see schematics, which show how a
ferrite-loaded antenna is combined with a capacitor, creating a
resonant circuit tuned to the 60 kHz (or whatever) radio signal.
The trick is fundamentally no different that the one used in an
ordinary battery-powered AM broadcast radio, which (in the older
designs) uses a ferrite-core multi-turn loop antenna, tuned to
resonate at AM broadcast frequencies using a variable capacitor
(typically a 365 pF maximum). The WWVB frequency is about 10% that of
signals at the low end of the AM broadcast band, so it's necessary to
use a larger-value capacitor to tune any given amount of ferrite
antenna inductance to the desired frequency, but it's the same method.
As to how it works... well, think of it this way (and this is just an
approximation). The high magnetic permeability of the ferrite acts as
a sort of "concentrator", so that more of the transmitted EM field
flows through the antenna than would be the case if the antenna had an
air or plastic core. And, the large number of turns of wire on the
antenna both increases the amount of signal produced by the EM field,
and adds enough inductance that it's possible to tune the antenna to
resonance with a reasonable-sized capacitor.
Google on "small loop antennas" for more background.
--
Dave Platt <(E-Mail Removed)> AE6EO
Friends of Jade Warrior home page:
http://www.radagast.org/jade-warrior
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