[time-nuts] Measuring the accurcy of a wrist watch

Ulrich Bangert df6jb at ulrich-bangert.de
Thu Apr 17 04:14:39 EDT 2014


Chris,

I do not own a guitar with single coil pickups but I will surely give it a
try to find out whether the humbuckers of my Gibson Firebird & SG Standard
will also do the trick!

Best regards

Ulrich

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Chris Albertson
> Gesendet: Mittwoch, 16. April 2014 20:56
> An: Tom Van Baak; Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Measuring the accurcy of a wrist watch
> 
> 
> I just did an experiment.  Place a simple quartz movement 
> wrist watch on top of a Fender Stratocaster guitar.  I get a 
> very strong and easy to detect signal.  A loud and sharpt 
> "ping" once per second.  More then 1 volt
> peak to peak.   I can cancel almost all the background hum 
> and hiss in the
> normal way by using the selector switch on the guitar.
> 
> The guitar has a pickup coil with many thousands of turns of 
> #40 wire.  With the selector with at #2 position there is a 
> second coil some inches away that is wound in the opposite 
> direction and the two are added canceling any field that is 
> filing the room.
> 
> I tried the same with a wall clock and all I had to do was 
> hold the clock an inch away.  The wrist watch was placed on 
> top of the strings a few mm above the bridge PU.
> 
> These is likely about 3 oz of #40 magnet wire on a guitar PU. 
>  If I were building a sensor I'd do it just like the guitar.  
> one coil to pick up the signal and another identical coil 
> some inches away to to pick up ambient "noise" and then wire 
> the two in parallel but in anti-phase.
> 
> If yu happen to have a guitar around, you have a watch sensor.
> 
> 
> On Wed, Apr 16, 2014 at 10:43 AM, Tom Van Baak 
> <tvb at leapsecond.com> wrote:
> 
> > > Tom,
> > >
> > > can you explain what exactly you understand by "a large coil of 
> > > wire"?
> >
> > Sorry, by large I meant a large number of turns; the coil itself is 
> > quite small. Rather the winding one myself I just used the 
> pickup coil 
> > from an old cheap plastic self-impulsed pendulum clock. The wire is 
> > extremely fine and there must be thousands of turns since the spool 
> > diameter is only 15-20mm and the net resistance is 3.5k. 
> Here are some 
> > iPhone photos I just
> > took:
> >
> > http://leapsecond.com/pages/Junghans/coil.htm
> >
> > > Did you make the easurements on the Junghans with a DIY sensor or 
> > > with
> > one
> > > of the commercially available?
> >
> > Both. The commercial ones sold by Bryan Mumford are excellent; his 
> > instrument includes signal conditioning, adjustable high gain, and 
> > other useful features. It's meant for watchmaker types with no 
> > electronics background. It works perfectly out of the box.
> >
> > The Junghans wristwatch is extremely well engineered for 
> long-life and 
> > the leaked magnetic signal is the weakest of any watch I've 
> measured. 
> > Still, it can be measured. The placement of the pickup coil on the 
> > watch face needs to be optimized for best "reception", or any 
> > reception at all for that matter.
> >
> > By contrast, a typical AAA-battery desk/wall quartz clock movement 
> > generates a huge magnetic signal. It is so clean that you 
> can clearly 
> > see both the start (+) of the impulse and the end (-) of 
> the impulse 
> > about 30 ms later. In fact I suspect it's actually 31.25 
> ms, or 1/32 
> > s, since that's 1024 cycles of a 32.768 kHz oscillator. See:
> >
> > sensor placement: 
> > http://leapsecond.com/pages/Junghans/quartz-clock.jpg
> > output to scope: http://leapsecond.com/pages/Junghans/coil-aa.gif
> >
> > > I have made some basic tests with a coil coming from a 
> loudspeaker's
> > cross
> > > over network. It has a few hundred windings, R=1.3 Ohms, 
> 2.3 mH, but 
> > > the only thing i receive with this coil is a strong 10 Mhz 
> > > signal...perhaps
> > no
> > > real surprise in a time nuts laboratory.
> >
> > I suspect your 1.3 ohms means the number of turns is far too low. I 
> > don't see any RF here, nor even very much 50/60 Hz.
> >
> > /tvb
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> 
> 
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California 
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