[time-nuts] Sidereal timekeeping

[Jean-Louis Oneto]

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: <iovane at inwind.it>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at 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.griffiths at xtra.co.nz>
>>To: "Discussion of precise time and frequency measurement"
>><time-nuts at 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, iovane at 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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>
>
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