From: "mike742" on Sun,Apr 17 2005 11:09 pm

I've always noted with some curiosity that 77.503kHz,
60.002kHz, and 60.005kHz are off-the-shelf crystals too...
used in a direct conversion receiver for DCF/WWV to 3Hz, 2Hz,
and 5Hz carrier-detect frequencies maybe?

Strange. Maybe another resonance mode?

I'd guess the specified frequency is parallel resonance with
the specified load capacitance.

I have some Digi-Key SE3320-ND 60 Khz xctls (C-2 60.000KC-P).

My best try at measuring the series resonant frequency shows
59998 Hz. Perhaps the 60.002 Khz ones are series resonant at
60000 Hz. I don't have any of those to measure.

To help us out, it would be best if you describe your
method of testing the resonance frequencies and the
accuracy of your frequency meter/counter.

A -2 Hz "error" in frequency is about 33 PPM (Parts
Per Million) or 0.0033 %. That seems to be within
manufacturer's stated tolerance.

For what it's worth, the spectral occupancy needed
by the WWVB signal is roughly 5 Hz. That is good
enough to demodulate the AM of WWVB and still
preserve the (relative) sharpness of the digital
amplitude transitions for purposes of obtaining the
correct time of day. Modulation on WWVB is roughly
30% AM at 1 second periodicity.

In my TRF receiver for 60 KHz, the carrier is
extracted by amplifying the filtered signal and
applying it to an over-driven MC1350P which acts
as a limiter. Outside of the (relatively) broad
selectivity of the tuned loop (Q roughly 45) and
an interstage L-C tuned coupling, the final filter
is simply two ECS crystals in series with a small
capacitor to ground at the series connection point.
The capacitor value was arrived at by "cut and
try" substitution, much quicker than trying to
calculate everything after an elaborate crystal
measurement exercise. :-)

The final selectivity is narrow enough to eliminate
most of the LF hash around the spectrum, especially
the 4th harmonics of the TV set horizontal sweep
frequency. That should work equally well on non-
limiting demodulation to get the time-of-day data.
[without the DSP supplied by the microcontrollers
in the radio clocks...we have two commercial units
in the house for that]

Measuring the exact crystal resonance frequency is
NOT a simple exercise at 60 KHz. I would suggest
looking closer at the Digi-Key links for technical
data direct from the manufacturer. Those are found
on the Digi-Key final part-number page just below
the electronic catalog page PDF link. Manufacturer's
data yields the parallel capacitance, maximum series
resonance crystal equivalent resistance, and either
the equivalent series inductance or the equivalent
series capacitance. Digi-Key is excellent in their
links to manufacturer's data in my estimation.