"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 Germany. 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. http://www.boulder.nist.gov/timefreq/ http://www.ptb.de/english/org/4/43/433/disse.htm http://www.npl.co.uk/npl/ctm/msf.html 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 -- Markus G. Kuhn, Security Group, Computer Lab, Cambridge University, UK email: mkuhn at acm.org, home page: <http://www.cl.cam.ac.uk/~mgk25/>