Or about half of what an atomic clock is at the discounters
and there the price includes a huge
display along with the receiver parts.

Oh, I'm all for cannibalizing the commercial clocks, what with their
pretuned ferrite loops, 60kHz receiver and demodulator, as a
cost-and-time-effective method. But if someone did want to roll their
own...

I have custom ordered tuning-fork style crystals down to 12kHz, and
they were way more than the mass-produced $1 jobbies! I think $30-$50
each in onesies. $1 is really cheap in comparison.

Tim.

Hello Rich,

Except for the fact that one receiver drove a Nixie display I never built
one with tubes. Now wouldn't that be something?

Yabbut, it'd be a little cumbersome for a wall clock. ;-)

In the shape of a mantle clock it would work. Open chassis, of course,
so the discerning visitor can admire. With nixies it would look really cool.

Regards, Joerg

http://www.analogconsultants.com

Hello Tim,

Oh, I'm all for cannibalizing the commercial clocks, what with their
pretuned ferrite loops, 60kHz receiver and demodulator, as a
cost-and-time-effective method. But if someone did want to roll their
own...

In that case I'd probably try to do it with a PLL stabilized
Q-multiplier instead of a crystal filter. Should work just fine at
60kHz. Or a conversion scheme that puts the IF in the low kHz range
where it can be done with active or switched capacitor filters. Still
have to stabilize the oscillator though. Just as a proof of concept...

I have custom ordered tuning-fork style crystals down to 12kHz, and
they were way more than the mass-produced $1 jobbies! I think $30-$50
each in onesies. $1 is really cheap in comparison.

True, $1 is cheap. Custom crystals are less and less popular. Some of
the companies I used way back when are no longer there or aren't doing
it anymore unless you buy thousands.

Regards, Joerg

http://www.analogconsultants.com

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.

My appologies for the late reply but what is a "PLL stabilized
Q-multiplier"?

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.

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.
....

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.

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.

I see what you're asking.

The Digi-Key pages says 100 ppm (+/- 6 Hz @ 60 Khz). The Epson
web page says they are photolithography-finished and at least
one Epson data sheet says the standard frequency tolerance is
20 ppm. Possibly they have no problem hitting 20 ppm and the
actual tolerance is much better than that (but not over
temperature).

20 ppm is still 1.2 Hz wide and the resonance probably is
sharper than that (Q 50K?).

This measuring project started when I tried to use the Epson
crystal data to calculate what the series resonant frequency
would be of the 60 Khz parallel specified crystals. After
much mucking around with various numbers I decided to measure
it.

And you're right, I've been ignoring calibration. Here's how
I'm measuring the resonance:

I have a homebrew LC VCO running at 6 Mhz. It's full frequency
range is about 5.99180 to 6.0053 Mhz. This is divided by 100
(two 74LS90's) and then low pass filtered resulting in a sine
wave around 60 Khz.

The signal level is attenuated via 10k/1k resistors and then fed
through the crystal with a 10k load on the other side. There's
some additional loading from the x100 gain amplifier and then
into a scope.

The circuit around the xctl looks like:
.1 10k
from-e-follower-lowpass--||----/\/\/\/\/----+---| xctl |----+--- to
x100 amp


1k 10k


gnd gnd

I can see a noise widened trace on the scope plus some
switching spikes/artifacts. As I tune the VCO, the noise
trace is flat except at one specific frequency, which is
about 1 Hz at most wide where the noise band becomes a sine
wave.

I'm measuring the frequency of the 6 Mhz VCO with a
Ramsey C-125 frequency counter. It's a standard ICM7216D
counter with a cheap 10 Mhz crystal as the time base. It's
uncalibrated (other than the factory, not sure of the date,
possibly in the 70s?).

Ok, how to calibrate the frequency counter?

And how stable is the frequency counter?

I'm living in a cloud of RF noise, plus computers. In addition
the frequency counter is a real RF noise generator too
(multiplexed LEDs in addition to the counting circuitry).

By moving the counter and short wave radio to a different room
I managed to hear the 2nd harmonic of a 5 Mhz crystal oscillator
on 10 Mhz with WWV. It sounded like the beat frequency was lower
in frequency than the 100 Hz WWV modulation pulses. So an upper
bound of +/- 100 Hz at 10 Mhz would put the upper bound on the
frequency counter of 10 ppm.

I'm not really happy with this calibration, I'll have to see what
I can do to improve it.

I'm not really happy with this calibration,
I'll have to see what I can do to improve it.

Zero-beat to WWV is hard to do better than 50Hz by ear. Mechanical
aids will get you a little better but then at the few Hz level you hit
variations in carrier due to ionospheric variation.

For a few hundred $, HP Z3801A's are available on the surplus market.
They're a 10MHz OCXO locked to GPS. Short term Allan variation is
10^-12 or better over 1-100 seconds. Many lab counters and a lot of
ham radio frequency counters will happily accept the 10MHz reference
that the Z3801A makes.

Other telecom-related GPS-locked OCXO's/rubidium oscillators are
available on the surplus market too, some make telco-related reference
frequencies like 1.544MHz or 19.6608MHz which can be used to calibrate
on.

Tim.

I read in sci.electronics.design that Tim Shoppa
wrote (in
.com) about 'wwvb
receiver chip needed', on Tue, 26 Apr 2005:

Zero-beat to WWV is hard to do better than 50Hz by ear.

Have you tried a Lissajou display?
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

"John Woodgate" wrote in message
...
I read in sci.electronics.design that Tim Shoppa
wrote (in
.com) about 'wwvb
receiver chip needed', on Tue, 26 Apr 2005:

Zero-beat to WWV is hard to do better than 50Hz by ear.

Have you tried a Lissajou display?
--

Or use the S-meter to see very low freq beats.