--- "Stephen W. Kercel" <[EMAIL PROTECTED]> wrote:
> Dave:
>
> From the 1 callsign, I expect that you are located in New England. If so,
> you're on the ragged edge of the normal coverage of WWVB. It is likely that
> the location is giving you as much trouble as the metal siding.
WWVB is by no means a "weak signal". But like everything thing else in
radio, "It's the signal-to-noise ratio, stupid!" :-)
Look for local noise sources. Much like an AM radio, "atomic clocks" use a
ferrite loopstick antenna for reception. The tiny receivers in them have a
sensitivity is on order of 0.5 uV. A tuning fork crystal provides
selectivity on the order of 10 Hz.
A loopstick antenna responds primarily to the magnetic component of
electromagnetic waves. Since magnetic fields follow an inverse cube
(rather than inverse square) law, if you've got an interference
problem with a magnetic probe antenna, the source is likey right under
your nose.
Keep your clock as far away from (and at right angles to) gadgets in your
home that might use switch-mode power supplies (EVEN if they are turned off!).
Our Sylvania color TV set is a prime generator of LF hash at my QTH, even
when the TV is off. It took me a year and a half to discover this -- by
accident!
Also, the 5th harmonic of any TV's horizontal oscillator is only a few
kHz from 60 kHz. Computer monitors sometimes cause problems as well.
I've heard that some UPS units use a switched-mode power supply operating
at 60 kHz. (Manufacturers have discovered the virues of RF, if only they
gave it the respect it deserves.)
"Atomic clocks" typically sync themselves periodically (typically during
the evening when signals are strongest, and noise levels subside). They
free-run on a 32.768 kHz oscillator, just like any other quartz-based
clock. Their "speed" is not under control of the precise 60 kHz carrier
to which they are tuned. Only spot checks are made to correct for timing
errors. In between, you're on your own.
Personally, I don't own an "atomic clock"... My story's different, but
directly related to my K2/100.
I'm in the process of developing a WWVB-based frequency standard that was
inspired by building and calibrating my K2/100 in 2003. When I tried to
beat a harmonic of the 4 MHz oscillator against WWV on 20 MHz for
calibration, and couldn't copy WWV on 20 MHz for many days (weeks?),
I knew I had to find a better approach. Having a test signal of known
precision would have been a nice way to perform the frequency counter
calibration.
I've made quite a lot of progress with the project, and have even used it
along with my K2 in the past two ARRL Frequency Measurement Tests with
very good results.
My antenna is a 40-turn air-core loop, 4-meters in circumference (that's
over 600 feet of wire!). I cheated and used 40 conductor ribbon cable to
build the loop. This feeds an Analog Devices instrumentation amplifier (to
maintain electrical balance) that is remotely powered by the receiver (the
antenna and preamp are in the attic). The rest is a secret (only kidding!),
but it involves balanced synchronous detection, zero IF (baseband) filtering,
and correlation decoding.
Incidentially, I cannot hear WWVB at all using an LF upconverter, a 75-meter
dipole, and my K2. All I hear is noise. Yet, I have SOLID copy, any day,
any time, on my specialized receiver, and I'm over 1600 miles from WWVB.
Kinda make you wonder what else is out there, doesn't it?
> If you cannot get it to come into sync within a week, then you probably do
> need an outdoor antenna. I'm sure that many participants in this reflector
> could come up with a practical way to build a 60 kHz external antenna and
> hook it to your clock. If I were doing it, I would look for one of the
> commercially made antennas that are designed for the time servers that some
> computer networks use.
Another approach might be to build a resonant loop (it can be smaller
than the one I described), and place it in proximity, (magnetically coupled)
to your "atomic clock". This would be similar to the "Select-A-Tenna"
(or similar devices) used to improve AM radio reception in fringe areas.
In closing, don't expect miracles from these clocks. They are simple
designs that perform best under high SNR conditions. They appear to be
too easily "fooled" by noise. They don't do WWVB justice.
73, de John, KD2BD
=====
Visit John on the Web at:
http://www.qsl.net/kd2bd/
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