[time-nuts] How Rubidiums make their frequency

Bill Hawkins bill at iaxs.net
Thu Apr 20 14:05:12 EDT 2006

Good point on the crystal frequency. It gets multiplied about 680 times.

IIRC, iron can be magnetized by jarring (striking) it while in a
magnetic field. Since you don't know the transportation history of
the device, degaussing is in order if the crystal is within lock range.

If degaussing is difficult, make sure that the C field changes smoothly
with the adjustment. A milliammeter in the line to the coils will work.
You won't see the change with a compass if the mu-metal shielding is
working (true?). Ah, can you damage mu-metal by striking it?

Bill Hawkins

Twenty years ago, my company installed CRT monitors in a titanium plant.
As luck would have it, the monitors were not far from a DC buss carrying
50,000 amps to the magnesium chloride electrolysis cells. When the DC
was turned on, the monitors showed the lower left quadrant of the screen
in the upper right quadrant. The customer was not amused. The problem was
fixed with mu-metal shields fit to the CRTs. Seems to me the mu-metal had
to be handled with care.

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
Behalf Of Rex
Sent: Thursday, April 20, 2006 4:56 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] How Rubidiums make their frequency (was
RE:time-nuts Digest, Vol 21, Issue 22)

On Thu, 20 Apr 2006 02:31:08 -0700, "Christopher Hoover"
<ch at murgatroid.com> wrote:
>Hi Tom,
>That's a good explanation, thank you.   I got that much already.  (While it
>took some time for my phyiscs, chemistry and semiconductor physics studies
>to kick back in, it all clicked last week.)   The Tracor, indeed, seems
>fairly ordinary compared to the other Rb's I have, going by the test points
>and the various labels inside.   There is the typical synthesizer section,
>audio demodulation section for the photocell, etc.
>So what I'm really wondering is this: is there a  wear mechanism or failure
>mode in the physics package that might explain why I have to crank the mag
>field almost to its high limit to get 5 MHz?  (This question presumes the
>mag field control is working properly, and I cannot say for sure that it
>-- Christopher.

I could be way off, but are you sure the xtal osc is centered on the
desired range?

Having the adjustment procedure for your unit would be a good advantage.
I got an Efretom rubidium a few years back that would not lock. I went
through all the proceedures and found that the crystal had drifted out
of the lock range. I was able to get it working but at the limit of the
xtal trimmer. Had to change a fixed capacitor to get it back near the
mid of the xtal trimmer.

So, I'm thinking I might have got it locked by messing with C field if I
had a problem like this. Would have locked but off correct freq.

Not sure if this is a reasonable discussion, you may have this stuff all
understood. Do you have the full service documentation?

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