[time-nuts] Fwd: HP5061B Versus HP5071 Cesium Line Frequencies

Donald E. Pauly trojancowboy at gmail.com
Fri May 26 19:34:04 EDT 2017


Those were interesting links. C field levels are a small fraction of
the earth's field of 700 milliGauss.  The C field winding is a few
turns inside the beam tube.  They are driven by several different
possible currents depending upon the desired frequency correction.
For the HP5061B it is 24.5 mA for the standard tube at 100%.  At the
0% point of the C field, the cesium resonance is unaffected.  At the
50% point, it is shifted upward by the amount of error in the
microwave frequency.  This varies depending on synthesizer design.  At
the 100% point, the error is reversed to give a reverse adjustment
range equal to the original error.

An electron orbits in a magnetic field with frequency f=qB/(2πm).
(q=charge, B=field strength, m=electron mass)  The Zeeman frequency is
the same as the frequency of an electron orbit in a field equal to 25%
of C field listed.  The square of the C field gives the frequency
shift in the cesium line.  I saw 90 mG listed for the 5062C but I
think that it should be 100 mG.

There is a test for the beam tube when the rf drive is removed and the
LF coil is driven with a frequency equal to half the Zeeman frequency.
It induces a peak that checks the operation of the tube without rf.
Does anyone know what is actually going on then?  We had a bad beam
tube that failed this test.

model|freq error cps|Zeeman freq kc|C field|(milliGauss)
5061A 2.50 53.53 76 mG
5061B 1.59 42.82 61 mG
5062C 4.30 70.40 (100 mG?)


---------- Forwarded message ----------
From: Tom Van Baak <tvb at leapsecond.com>
Date: Thu, May 25, 2017 at 9:23 PM
Subject: Re: [time-nuts] HP5061B Versus HP5071 Cesium Line Frequencies
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>


You're familiar with the 9,192,631,770 Hz definition of the SI second;
but that's only for an "unperturbed" atom. The bad news is that in
order to make the cesium beam operate at the central resonance peak
one actually has to violate the SI definition and perturb it -- by
applying a magnetic field (the so-called C-field), as well as other
factors. This cannot be avoided. The good news is that the shift can
be calculated.

In other words, because a magnetic field must be applied the actual
cesium resonance frequency is not 9192.631770 MHz. The synthesizer
locks to the peak, but the peak is at a slightly higher frequency than
the nominal book value. This detailed note from hp may help:


Different model beam tubes use different field strength / Zeeman
frequency. Search the archives for lots of good postings about all
these magic frequencies -- google: site:febo.com zeeman

If you want to see what the resonance peaks (all 7 of them) actually
look after the C-field is applied see:

and (poster size):

See also John's version:


One final comment -- the perturbed vs. unperturbed issue is far more
complex than a single correction. To get an idea of the math and
physics complexity of a laboratory Cs beam standard read some of



----- Original Message -----
From: "Donald E. Pauly" <trojancowboy at gmail.com>
To: "time-nuts" <time-nuts at febo.com>; "Donald E. Pauly" <trojancowboy at gmail.com>
Sent: Thursday, May 25, 2017 7:55 PM
Subject: [time-nuts] HP5061B Versus HP5071 Cesium Line Frequencies


The synthesizer in the HP5061B generates a frequency of about
9,192,631,772.5 cps when the 5 mc oscillator is exactly on frequency.
First the 5 mc oscillator is multiplied by 18 to 90 mc on the A1
board.  That in turn is multiplied by 102 in the A4 board to give
9,180 mc.

The 5 mc is also divided by 4079 to produce 1,225.790635 cps.  That in
turn is multiplied by 10,305 to produce 12,631,772.5 cps.  This is
added to the 9180 mc in the A4 mixer to produce the final frequency of
9,192,631,772.5 cps approximately.  This is higher than the defined
frequency of 9,192,631,770 cps by about 2.5 cps or 271·10^-12.  If I
figured it right, the C field adjustment only has a range of
40·10^-12.  This seems to be insufficient to put the standard on

Can anyone explain these mysteries?  Does anyone know why this
frequency was chosen?  Does anyone know the choice for the frequency
of the HP5071 cesium?

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