I realized that there was lot of way to avoid this [pulldown] problem, but
as I said, it was a long time ago (around 1976...), I was young and
inexperimented, and I just tried once on an almost broken 5 FF (~$1)
wristwatch, then I decided that the software approach would be better for
me.
I used a fine-grained handheld sharpening stone very carefully and just a
few light touchs were enough (um, rather too much!).
It also depends on what precision you're expecting. I hoped to reach few
seconds a day and it was rather tens of second or few minutes. Not so bad,
but if I had to reset the sidereal time once a day, it was almost useless
for me... At that time, I ended with a small program on an HP-65 (then
latter transposed to an HP-41CV), and I soon added a small star catalog
including proper motion and precession data for all the targets we were
working on at that time (Optical interferometry with aperture synthesis).
YMMV...
Regards,
Jean-Louis
----- Original Message -----
From: <iov...@inwind.it>
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Sent: Tuesday, May 17, 2011 1:05 PM
Subject: Re: [time-nuts] Sidereal timekeeping
Hi Jean-Louis,
I'm pleased to hear that you had success trying to modify such a crystal,
though you had problems checking the frequency.
Regarding this aspect that I'm aware of, my idea is to "hear" to the 32kHz
signal with a HP3586A selective voltmeter or a R&S VLF receiver. Further,
as
electric-guitar players do know, the 1 pps pulse of wristwatches is easily
picked up by guitar pickups (many use wristwatches to check pick-ups).
These
pulses could be compared to pulses coming from, say, a properly set 3325A.
And
I will use a wall-clock machine which I suppose is stronger than a
wristwatch.
As there is no issue, to some extent, with the lenght of wires between the
crystal and the circuit at these frequencies, I was also speculating about
a
quasi-continuous monitoring of the trimming process, where for trimming I
could
use a disc of lapping sheet glued to a Dremel disc.
Well, just arrived another suggestion from Bob LaJeunesse too.
Regarding software applets (your other post) I have several of them, but
as I
said my problem is different.
Thanks,
Antonio I8IOV
Hello list,
I tried that a long time ago, but the trap I went into was that the
capacitance of the 'scope probe was pulling the frequency down, so I ended
with a crystal too high in frequency...
I'm not sure that you can control the frequency without significantly
perturbing it. And waiting to check the rate between each tuning step
would
take a long time...
Regards,
Jean-Louis
----- Original Message -----
From: "Bruce Griffiths" <bruce.griffi...@xtra.co.nz>
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Sent: Tuesday, May 17, 2011 1:22 AM
Subject: Re: [time-nuts] Sidereal timekeeping
Jim Lux wrote:
On 5/16/11 2:58 PM, iov...@inwind.it wrote:
Neville,
at present I have not enough skill with micros to solve the problem.
I think I will try modifying a crystal. This would not be that
difficult
using
a lapping sheet or the like. And opening the can would be quite easy
using hot
air.
or a fine jeweler's saw or tubing cutter.
As you pointed out, the crystals are cheap, so you can afford to ruin a
few while figuring out how to do it.
(and then, remember us all, when you're a multi-billionaire having
cornered the market on sidereal rate crystals<grin>)
Since the 32 kHz crystal is likely to be a tuning fork form, one merely
needs to shorten the tines to increase the frequency.
It may be feasible to do this without removing any of the electrode
metallization.
Bruce
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