[ntp:questions] Re: WWVB 60kHz Receiver

John Ackermann N8UR jra at febo.com
Sun Apr 16 12:58:49 UTC 2006


Hi Dave --

We've chatted about your WWVB problems in the past, and you seem to have
a real collection of noisemakers that cause problems.  On the other
hand, I get really good reception here in Ohio.  I'm using the
Spectracom ferrite antenna (with internal preamp) up on the roof of my
house, and don't have any major spark generators nearby.  I do, however,
have challenges of my own with a few AM broadcasters that put in very
strong signals.  The BCB power coming down the coax of my wideband LF
antenna is so great that my LORAN receiver shows a diurnal phase shift
when the broadcaster changes antenna pattern at sunrise and sunset.

I get very good signal strength, and the 8170 loses lock maybe once
every 10 days; I've never actually seen the "lock" LED go off when I was
there.

I just looked at the NIST WWVB page, and it looks like the experiment
they were doing with the modulation depth has become permanent -- the
advertised power drop is now 17dB instead of the 10dB it used to be.  I
wonder if that might have a negative effect on some users, particularly
if they are competing with a lot of local noise.

I guess from Dave's, and my, experience you can draw the conclusion that
WWVB reception quality may be very dependent on the local environment.

By the way -- despite my fondness for LF, I'll readily acknowledge that
GPS is certainly a better time source in a whole bunch of ways, as long
as you can see the sky.

John
----
David L. Mills said the following on 04/15/2006 11:31 PM:
> John, et al,
> 
> You are not going to like this.
> 
> I;ve been running several WWVB clocks since 1981 using Spectracom 8170
> and Netclock/2 receivers with the NTP WWVB driver. NIST Time and
> Frequency Services, NIST Special Publication 462 (Revised 1990), claims
> nominal timecode accuracy of 100 microseconds, and that's what I got in
> the beginning.
> 
> 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.
> 
> This was bad enough, but then we started installing banks of UPS units
> in the machine room and they scream like banshees on 60 kHz, even with
> the antenna on the roof of an outbuilding. The result was total failure
> of all our WWVB radios, at least on campus.
> 
> Until recently I was getting good results at home, but now I see the
> signal has failed there as well, probably due to increased crud at 60
> kHz due some incidental radiator. I conclude WWVB is no longer useful
> here and I suspect in any machine room, unless the antenna is far away
> from the UPSes and with suitable ferrite decoupling.
> 
> A solution that would probably work for business is to locate the
> antenna and radio in a doghouse on the roof and run serial cable to the
> machine room. Lemme tell you how hard that is with a plastic sheet roof
> and a landlord that believes rooftop space rental for tenant machinery
> is a significant revenue stream.
> 
> Dave




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