From Newsgroup: sci.electronics.design

Bac in the early 80s, I nade a lot of money selling 'better than normal accuracy' digital watches. A colleague designed and made an accuracy
tester that showed +/- 20 seconds/month. The source accuracy was from
MSF Rugby RF transmitter ( 1 pulse/second?). The detector ( I think) was
some form of piezo... it was about 2mm diameter glued into a BNC housing
( for simplicity). It worked by touching the piezo probe onto the back
of the watch ( with the back off) and I was able to adjust the trim cap
to get close to a few seconds per month ( ignore ambient/body temp)
This probe went into the box via a cable, was amplified and somehow
comaped to the source and converted into secs/month.
Can anyone figure out how this probe was constructed?
Reason- I want to build another one with a 10Mhz reference Xtal etc.
any suggestions welcomed.
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From Newsgroup: sci.electronics.design

On 8/01/2026 2:41 am, TTman wrote:

Bac in the early 80s, I nade a lot of money selling 'better than normal accuracy' digital watches. A colleague designed and made an accuracy
tester that showed +/- 20 seconds/month. The source accuracy was from
MSF Rugby RF transmitter ( 1 pulse/second?). The detector ( I think) was some form of piezo... it was about 2mm diameter glued into a BNC housing
( for simplicity). It worked by touching the piezo probe onto the back
of the watch ( with the back off) and I was able to adjust the trim cap
to get close to a few seconds per month ( ignore ambient/body temp)
This probe went into the box via a cable, was amplified and somehow
comaped to the source and converted into secs/month.
Can anyone figure out how this probe was constructed?
Reason- I want to build another one with a 10Mhz reference Xtal etc.
any suggestions welcomed.

Don't bother. 10MHz reference crystal aren't all that accurate. Get a
rubidium stabilised source if you can't pull a proper reference out of
the ether. Global positioning system reference frequencies are lot more accurate than any 10MHz reference crystal, and there are other broadcast frequencies which are almost as good.

The standard watch crystal is a 32,768kHz piezo fork, and if you put one
close to the metalwork around an active crystal in watch it would
presumably get mechanically excited by the watch crystal, and you should
be able detect an electrical signal on it's leads that would track
frequency being generated inside the watch.

The sensing crystal is unlikely to be resonant at exactly the same
frequency inside the watch so there would be a little phase lead or lag between them, but it would be stable.

I've never seen it done, but it ought to work.
--
Bill Sloman, Sydney
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From Newsgroup: sci.electronics.design

On 07/01/2026 15:41, TTman wrote:

Bac in the early 80s, I nade a lot of money selling 'better than normal accuracy' digital watches. A colleague designed and made an accuracy
tester that showed +/- 20 seconds/month. The source accuracy was from
MSF Rugby RF transmitter ( 1 pulse/second?). The detector ( I think) was some form of piezo... it was about 2mm diameter glued into a BNC housing
( for simplicity). It worked by touching the piezo probe onto the back
of the watch ( with the back off) and I was able to adjust the trim cap
to get close to a few seconds per month ( ignore ambient/body temp)

Watches tend to have better stability than wall clocks because for more
than half the time they are clamped to roughly body temperature. Some
kit today uses GPS when available to set its local clock.

This probe went into the box via a cable, was amplified and somehow
comaped to the source and converted into secs/month.
Can anyone figure out how this probe was constructed?
Reason- I want to build another one with a 10Mhz reference Xtal etc.
any suggestions welcomed.

I suspect it was a high Q tank circuit or a watch crystal tuned to
nominal ~32768Hz to act as a passive amplifier of the stray radiation
from the watch oscillator. Amplify to a logic level and count number of
pulses over fixed time intervals from the stable reference source.

Unless you oven the crystal and calibrate it periodically you really
want a better reference standard. MSF Rugby or equivalent is pretty good
for 1 to 10000s delays so long as the dew has evaporated (after ~10am).

We used MSF as a time reference to discipline local Rb clocks for early
low frequency interferometry and could easily detect diurnal shifts in
their pulse timing due to loading of the transmitter when the ground had
dew on it in the mornings and late at night.

You can do it the slow way over a few days against any cheap domestic
atomic clock. I doubt if it is really worth the effort of making such a
tester today. So many smart watches use the internet or GPS for time
reference that they are already well synced.
--
Martin Brown

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From Newsgroup: sci.electronics.design

On Wed, 7 Jan 2026 15:41:04 +0000, TTman <kraken.sankey@gmail.com>
wrote:

Bac in the early 80s, I nade a lot of money selling 'better than normal >accuracy' digital watches. A colleague designed and made an accuracy
tester that showed +/- 20 seconds/month. The source accuracy was from
MSF Rugby RF transmitter ( 1 pulse/second?). The detector ( I think) was >some form of piezo... it was about 2mm diameter glued into a BNC housing
( for simplicity). It worked by touching the piezo probe onto the back
of the watch ( with the back off) and I was able to adjust the trim cap
to get close to a few seconds per month ( ignore ambient/body temp)
This probe went into the box via a cable, was amplified and somehow
comaped to the source and converted into secs/month.
Can anyone figure out how this probe was constructed?
Reason- I want to build another one with a 10Mhz reference Xtal etc.
any suggestions welcomed.

The digital display probably emits EMI at the display refresh rate,
that with any luck is tied to the frequency reference crystal (32
KHz).

The metal case will block electrical signals but not low-frequency
magnetic signals.

So use a ferrite-cored solenoid to pick up magnetic signals and
analyze them.

Joe
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From Newsgroup: sci.electronics.design

On Wed, 7 Jan 2026 15:41:04 +0000, TTman <kraken.sankey@gmail.com>
wrote:

Bac in the early 80s, I nade a lot of money selling 'better than normal >accuracy' digital watches. A colleague designed and made an accuracy
tester that showed +/- 20 seconds/month. The source accuracy was from
MSF Rugby RF transmitter ( 1 pulse/second?). The detector ( I think) was >some form of piezo... it was about 2mm diameter glued into a BNC housing
( for simplicity). It worked by touching the piezo probe onto the back
of the watch ( with the back off) and I was able to adjust the trim cap
to get close to a few seconds per month ( ignore ambient/body temp)
This probe went into the box via a cable, was amplified and somehow
comaped to the source and converted into secs/month.
Can anyone figure out how this probe was constructed?
Reason- I want to build another one with a 10Mhz reference Xtal etc.
any suggestions welcomed.

I'd expect that removing the back affects the oscillator frequency.


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
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From Newsgroup: sci.electronics.design

On 07/01/2026 17:53, john larkin wrote:

On Wed, 7 Jan 2026 15:41:04 +0000, TTman <kraken.sankey@gmail.com>
wrote:

Bac in the early 80s, I nade a lot of money selling 'better than normal
accuracy' digital watches. A colleague designed and made an accuracy
tester that showed +/- 20 seconds/month. The source accuracy was from
MSF Rugby RF transmitter ( 1 pulse/second?). The detector ( I think) was
some form of piezo... it was about 2mm diameter glued into a BNC housing
( for simplicity). It worked by touching the piezo probe onto the back
of the watch ( with the back off) and I was able to adjust the trim cap
to get close to a few seconds per month ( ignore ambient/body temp)
This probe went into the box via a cable, was amplified and somehow
comaped to the source and converted into secs/month.
Can anyone figure out how this probe was constructed?
Reason- I want to build another one with a 10Mhz reference Xtal etc.
any suggestions welcomed.

I'd expect that removing the back affects the oscillator frequency.

More than likely... but a re test after adjustment and the back replaced
would cover that. Could what I thought was a 'piezo' at the end of the
probe just have been a piece of wire?

John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics

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From Newsgroup: sci.electronics.design

On 1/7/26 22:38, TTman wrote:

On 07/01/2026 17:53, john larkin wrote:

On Wed, 7 Jan 2026 15:41:04 +0000, TTman <kraken.sankey@gmail.com>
wrote:

Bac in the early 80s, I nade a lot of money selling 'better than normal
accuracy' digital watches. A colleague designed and made an accuracy
tester that showed +/- 20 seconds/month. The source accuracy was from
MSF Rugby RF transmitter ( 1 pulse/second?). The detector ( I think) was >>> some form of piezo... it was about 2mm diameter glued into a BNC housing >>> ( for simplicity). It worked by touching the piezo probe onto the back
of the watch ( with the back off) and I was able to adjust the trim cap
to get close to a few seconds per month ( ignore ambient/body temp)
This probe went into the box via a cable, was amplified and somehow
comaped to the source and converted into secs/month.
Can anyone figure out how this probe was constructed?
Reason- I want to build another one with a 10Mhz reference Xtal etc.
any suggestions welcomed.

I'd expect that removing the back affects the oscillator frequency.

More than likely... but a re test after adjustment and the back replaced would cover that. Could what I thought was a 'piezo' at the end of the
probe just have been a piece of wire?

John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics

I think the coupling was quite possibly acoustic rather than electric.

Jeroen Belleman
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From Newsgroup: sci.electronics.design

TTman <kraken.sankey@gmail.com>wrote:

Bac in the early 80s, I nade a lot of money selling 'better than normal >accuracy' digital watches. A colleague designed and made an accuracy

tester that showed +/- 20 seconds/month. The source accuracy was from
MSF Rugby RF transmitter ( 1 pulse/second?). The detector ( I think) was >some form of piezo... it was about 2mm diameter glued into a BNC housing
( for simplicity). It worked by touching the piezo probe onto the back
of the watch ( with the back off) and I was able to adjust the trim cap
to get close to a few seconds per month ( ignore ambient/body temp)
This probe went into the box via a cable, was amplified and somehow
comaped to the source and converted into secs/month.
Can anyone figure out how this probe was constructed?
Reason- I want to build another one with a 10Mhz reference Xtal etc.
any suggestions welcomed.

I am wearing a Casio radio watch that automatically syncs to DCF77
https://en.wikipedia.org/wiki/Casio_Wave_Ceptor

I also have a Rubidium 10 MHz reference generator from ebay.

I think maybe use a 10 MHz piezo mounted against the watch as detector?
There are several piezo sensors for that frequency,
From:
https://duckduckgo.com/?q=10+MHz+Piezo+sensor
https://acs-international.com/instruments/transducers/piezoelectric-1-10-mhz/

Or maybe you can just pick up the watch's 10 MHz oscillator with a small antenna close to the watch,

Check / try with your shortwave radio on SSB with local oscillator should hear a tone.
Then build a small RF 10 Mhz tuned amplifer?


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From Newsgroup: sci.electronics.design

Jan Panteltje <alien@comet.invalid>wrote:

TTman <kraken.sankey@gmail.com>wrote:
Bac in the early 80s, I nade a lot of money selling 'better than normal >>accuracy' digital watches. A colleague designed and made an accuracy >>tester that showed +/- 20 seconds/month. The source accuracy was from

MSF Rugby RF transmitter ( 1 pulse/second?). The detector ( I think) was >>some form of piezo... it was about 2mm diameter glued into a BNC housing
( for simplicity). It worked by touching the piezo probe onto the back
of the watch ( with the back off) and I was able to adjust the trim cap
to get close to a few seconds per month ( ignore ambient/body temp)
This probe went into the box via a cable, was amplified and somehow >>comaped to the source and converted into secs/month.
Can anyone figure out how this probe was constructed?
Reason- I want to build another one with a 10Mhz reference Xtal etc.
any suggestions welcomed.

I am wearing a Casio radio watch that automatically syncs to DCF77
https://en.wikipedia.org/wiki/Casio_Wave_Ceptor

I also have a Rubidium 10 MHz reference generator from ebay.

I think maybe use a 10 MHz piezo mounted against the watch as detector?
There are several piezo sensors for that frequency,
From:
https://duckduckgo.com/?q=10+MHz+Piezo+sensor
https://acs-international.com/instruments/transducers/piezoelectric-1-10-mhz/

Or maybe you can just pick up the watch's 10 MHz oscillator with a small antenna close to the watch,

Check / try with your shortwave radio on SSB with local oscillator should hear a tone.
Then build a small RF 10 Mhz tuned amplifer?

Or 32 kHz if that is the crystal.
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From Newsgroup: sci.electronics.design

On 08/01/2026 04:56, Jan Panteltje wrote:

Jan Panteltje <alien@comet.invalid>wrote:

I am wearing a Casio radio watch that automatically syncs to DCF77
https://en.wikipedia.org/wiki/Casio_Wave_Ceptor

I also have a Rubidium 10 MHz reference generator from ebay.

I think maybe use a 10 MHz piezo mounted against the watch as detector?
There are several piezo sensors for that frequency,
From:
https://duckduckgo.com/?q=10+MHz+Piezo+sensor
https://acs-international.com/instruments/transducers/piezoelectric-1-10-mhz/

Or maybe you can just pick up the watch's 10 MHz oscillator with a small antenna close to the watch,

Check / try with your shortwave radio on SSB with local oscillator should hear a tone.
Then build a small RF 10 Mhz tuned amplifer?

Or 32 kHz if that is the crystal.

Watches are almost always 32kHz crystals at ultra low power.
Higher frequencies require too much current!
--
Martin Brown

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From Newsgroup: sci.electronics.design

Martin Brown <'''newspam'''@nonad.co.uk>wrote:

On 08/01/2026 04:56, Jan Panteltje wrote:

Jan Panteltje <alien@comet.invalid>wrote:

I am wearing a Casio radio watch that automatically syncs to DCF77
https://en.wikipedia.org/wiki/Casio_Wave_Ceptor

I also have a Rubidium 10 MHz reference generator from ebay.

I think maybe use a 10 MHz piezo mounted against the watch as detector?
There are several piezo sensors for that frequency,
From:
https://duckduckgo.com/?q=10+MHz+Piezo+sensor
https://acs-international.com/instruments/transducers/piezoelectric-1-10-mhz/

Or maybe you can just pick up the watch's 10 MHz oscillator with a small antenna close to the watch,

Check / try with your shortwave radio on SSB with local oscillator should hear a tone.
Then build a small RF 10 Mhz tuned amplifer?

Or 32 kHz if that is the crystal.

Watches are almost always 32kHz crystals at ultra low power.
Higher frequencies require too much current!

True, you could try listening to the harmonics with a good radio too,
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From Newsgroup: sci.electronics.design

I also have a Rubidium 10 MHz reference generator from ebay.

I think maybe use a 10 MHz piezo mounted against the watch as detector? >>>> There are several piezo sensors for that frequency,
From:
https://duckduckgo.com/?q=10+MHz+Piezo+sensor
https://acs-international.com/instruments/transducers/piezoelectric-1-10-mhz/

I've ordered 5 of those to play with. I bought a 'watch' tester from
ali, stripped out and saw it had a piezo strapped across 2 metal pins
that the watch is held against. These seem to be designed for quartz
analogue watches- the app detects the missing motor pulses to correct
the time..( as opposed to 'pulling' the crystal like they did in the old
days)
In the box, the piezo is connected to an LM386 ( !) and a USB comms
chip to send data to the app. I can play some more now.
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