How can such a small device -- a wrist watch -- receive such long-wave radio signals?
 

I want to know how such a tiny device can operate at such a long
wavelength. Unfortunately, that info is classified by the FBI/CIA, and
then won't let me or any USA citizen find out about it.


No X-files stuff needed.....

The secret is that the receiver only needs a tiny amount of bandwidth,
not more than a few hertz.
So even with a teensy, tiny, itsy-bitsy, microscopic signal, all that
an antenna that's much shorter than a wavelength can capture, that's
still enough signal to be discernible.

A cheap and simple 60KHz crystal filter has under one Hertz
bandwidth. 60KHz mini crystals are like 32 cents each at digi-key.

Voila!

How can such a small device -- a wrist watch -- receive such long-wave radio signals?
 

Ancient_Hacker hath wroth:

The secret is that the receiver only needs a tiny amount of bandwidth,
not more than a few hertz.

It hertz to think about it.

So even with a teensy, tiny, itsy-bitsy, microscopic signal, all that
an antenna that's much shorter than a wavelength can capture, that's
still enough signal to be discernible.

A cheap and simple 60KHz crystal filter has under one Hertz
bandwidth. 60KHz mini crystals are like 32 cents each at digi-key.

Less than 1Hz BW won't work for WWVB.

From:
WWVB Radio Controlled Clocks:
Recommended Practices for Manufacturers and Consumers
http://tf.nist.gov/general/pdf/1976.pdf
Section 8A.
"The RF bandwidth of the receiver should be narrow,
typically ±10 Hz or less."

The data rate of WWVB is 1 bit/sec, which occupies about 4Hz bandwidth
in a practical receiver. The bandwidth also needs to compensate for
2x6 tuning fork crystal tolerance and drift which can vary radically
by vendor and quality:
http://www.worldbond.com/quartz-fork.php
±50ppm initial accuracy yields ±3Hz, which is where the rather wide
20Hz bandwidth spec came from.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558