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Roy Lewallen wrote:
I played with that many, many moons ago. The bugaboo is local noise -- QRM from all kinds of devices running from mains power, switching, arcing, and sparking. The noise was lower late at night when more gadgets were off, which I'm sure is why the automatic clocks you can get now do their synchronizing late at night. So I suggest looking at each architechture for its noise immunity and how it responds when it does get a burst of noise. Absolute minimum bandwidth is an advantage from a noise standpoint, as long as it's not so narrow that it rings for too long when hit with an impulse. A PLL with long loop time constant might be a good idea, since it should maintain synchronization through a noise burst. Other than those generalities, I don't have much to offer. I built up a simple receiver long ago that allowed me to see the binary code on a scope, but only late at night. I never pursued perfecting it to the point where it would be reliable. WWVB increased its power between then and now, but it's probably still not a piece of cake. Roy Lewallen, W7EL Joel Kolstad wrote: I've been thinking about building a WWVB (time code on 60kHz) receiver, and wanted to get some suggestions for the architecture. Poking around the web some, I did find one receiver where the guy built a synchronous detector using a PLL and VCXO to phase-lock to the 60kHz carrier. Nice idea -- especially since he wanted the 60kHz carrier as a synchronization signal. However, I just want the time data... so... wouldn't it be easier to build a mixer at, e.g., 59kHz and then use an envelope detector to get a loud/quiet audible (1kHz) tone (WWVB reduces power by 10dB to signify 0 bits in its time code)? It seems to me that this approach avoids the need for the PLL and VCXO, which is a nice 'reduction' in complexity. Also, since I'll have a microcontroller around to decode the time code anyway, it can easily generate the 59kHz signal. Thanks, ---Joel Kolstad I would suggest using a shielded loop antenna to help with the local noise problem. The loop is directional so it could be oriented to reduce at least one source of noise. Bill K7NOM |
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