Radio Clocks

Markus Kuhn Markus.Kuhn at
Sun Oct 11 16:32:50 UTC 1998

"Richard L. Shockney" wrote on 1998-10-11 15:38 UTC:
> BTW, there are a few of these on the (U.S.) market that use radio
> frequencies to automatically adjust to the U.S. Atomic Clock. As I recall,
> the wrist watch was about $900, the analog wall clock about $200 and the
> digital clock/radio about $100 (all U.S. dollars).

These clocks are probably based on WWV, which is a short wave
transmitter, for which receivers are a bit more expensive than for
long-wave transmission. The German DCF77 is a very powerful (50 kW)
long-wave transmitter. Long-wave radiation has the advantage that it
penetrates buildings quite well, so you do not need external antennas
and your clocks work in every room. I used to have a DCF77 wrist watch
for around $50, and I have connected to the serial port of my Linux box
a DCF77 receiver for around $20. Since suitable long-wave receivers can
be implemented in a very simple chip design with practically the only
external component being the receiver coil/capacitor combination, you
find DCF77 more and more often in lowest cost products (< $50) in

NIST also operates a WWVB 60 kHz long-wave service in the US, but I it
has a much weaker signal than DCF77 (50 kW). WWVB used to have 10 kW for
a long time and was only very recently upgraded to 23 kW, with plans for
further upgrades to 35-40 kW. The British Telecom transmitter MSF in
Rugby has 27 kW at 60 kHz.

Once these WWVB upgrades have been completed, I would expect that you
might also get in the US mass market radio clocks that are as cheap as
those in Central Europe.


Markus G. Kuhn, Security Group, Computer Lab, Cambridge University, UK
email: mkuhn at,  home page: <>

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