[ntp:questions] Re: WWVB 60kHz Receiver

David L. Mills mills at udel.edu
Mon Apr 17 03:11:20 UTC 2006


Hal,

THe Spectracom receiver is actually very good. It can pull the signal 
from beneath the noise (literally), but doesn't do well with cochannel 
signals. What I saw on the scope was a substantial carrier modulated 
with 60-Hz square wave(!). That's why I suspect an arc welder. I called 
in the power company and they were quite cooperative (heck; they were 
hams themselves). It was easy to verify the crud quickly dived under the 
noise when more than a couple hundred feet from the power line. I could 
probably fix it at home with line filters.

Outboard DSP might help, but I would DC coupling and the only thing I 
have around for that is an old DSP93. Heck; not this year.

Dave

Hal Murray wrote:
>>The WWVB signal has become degraded in recent years and now all WWVB 
>>receivers here have been retired. Here in Delaware we are on the 100 
>>microvolt per meter contour (before the WWVB transmitter upgrade) and 
>>normally this would be sufficient for good accuracy. However, at least 
>>here in Newark, there is another strong signal on 60 kHz that interferes 
>>with WWVB. I chased this down to power-line conducted EMI and found the 
>>interferiing signal was well above the noise several miles from campus. 
>>It's not clear where it originates, but the prime suspect is a power 
>>inverter for an arc welder at the Chrysler plant in town.
> 
> 
> I'm not a wizard at this stuff.  CPUs are cheap these days.
> 
> Would it be possible to pull the signal out of the junk
> with some serious DSP hacking?
> 
> At the back of an envelope level, how would one answer
> that question?
> 
> On the other hand, NIST recently upgraded the transmitter
> at WWVB, so somebody must think this is a valuable service.
> Do they have anybody tracking the EMI issues?
> 
> Who uses WWVB these days?  Have serious time hackers all switched
> to GPS, leaving "atomic clocks" as the only customer?
> 




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