[time-nuts] Zeeman frequency oddness

paul swed paulswedb at gmail.com
Sat Oct 27 16:55:46 EDT 2012


John
Going from what you have here and the information below it would seem to me
that there is some form of residual magnetism effecting the tube. I don't
believe the waveform of the signal has a huge effect as long as its not a
square wave. I think it can have distortion.

Its been a while but since you have an accurate reference, I believe you
can adjust the system to align to that and see what pip on the zeeman you
end up on. Perhaps you are aligning to the wrong pip. Go to either of the
lower ones and see if it works better or lines up. If it does then the math
holds and refines the question.

There was an old HP doc that evidently it was very easy to align to the
wrong pip. It was quite a problem actually.
Regards
Paul
WB8TSL

On Sat, Oct 27, 2012 at 3:16 PM, John Ackermann N8UR <jra at febo.com> wrote:

> Since I recently got an HP Cs degausser (thanks, Stijn!), I though I'd go
> through the whole setup routine for my 5061B/004 and see how close the
> C-field-via-Zeeman setting would bring me to GPS-derived frequency.  It
> turned out to be an interesting and puzzling exercise.
>
> This 5061 seems to be in perfect working order -- quick lock, good meter
> readings, and measurements indicate frequency within parts in e12.  I don't
> have any reason to believe that it's not tuned or working properly, except
> for the Zeeman-setting results.
>
> The problem is that when I tune the audio source around 53.53 kHz, per
> both the manual and the sticker on the door, I don't see any change in Beam
> I at all.  Nor do I see anything at the alternate frequency of 42.82 kHz.
>
> Instead, I see the expected three peaks -- primary with a smaller
> secondary on either side -- at about 48.21 kHz, which doesn't show up
> anywhere in the literature I've found.
>
> Below, I've cut and pasted a years-old message from TVB and Corby that
> explains the Zeeman frequencies.  I've measured the synthesizer output and
> it's nominally 12.6317725 MHz, which per that message should correspond to
> a 53.53 Zeeman.  Where 48.21 kHz comes from, I have no idea.
>
> I'm using a Rigol arbitrary function generator locked to an external
> reference as the audio source, in sine wave mode.  I know that's not the
> cleanest device in the world, but the wave doesn't look too bad on my scope
> and a counter indicates the frequency is what the dial says.  As I adjust
> the audio amplitude, the beam current responds, and I see a peak at around
> 500mV, which the 5061B manual says is correct.
>
> Any ideas why I might be seeing this very off-the-wall result?  Could
> distortion in the audio source cause something like this?  I'm more
> inclined to blame technique or gremlins than the 5061B -- again, external
> measurements indicate that the thing is tuned correctly and operating
> properly, just having this goofy Zeeman response.
>
> Thanks!
>
> John
>
>
> [time-nuts] Zeeman frequency and cesium tube interchange
> Tom Van Baak
> Fri Apr 22 13:32:35 EDT 2005
>
> Hi Brian,
>
> The SI second is defined for mean sea level and no
> external fields.
>
> If there were no magnetic field, in theory, a cesium
> tube would show a resonance when its synthesizer
> generated exactly 9192.631770 MHz; the definition
> of the second.
>
> But in practice, a weak uniform magnetic field is
> necessary for the beam apparatus to operate; to
> isolate the center peak from the other peaks. This
> DC field also has the side-effect of slightly shifting
> the frequency of the center line.
>
> Fortunately the frequency shift is a calculatable
> amount (a function of magnetic field strength) so
> the trick is that the synthesizer must be designed
> to generate a slightly higher frequency to exactly
> compensate for the shift that will be induced by
> the field.
>
> Thus the synthesizer for a 5061A does not actually
> generate 9192 631 770 Hz as one might expect,
> but because of the nominal 61 milligauss C-field,
> the synthesizer must generate 9192 631 771.6 Hz
> in order to lock onto the Cs peak precisely. The
> Zeeman frequency for 61 mG is 42.82 kHz (info
> from an old 5061A manual).
>
> Other 5061A/B use a 76 mG field, corresponding
> to a 53.53 kHz Zeeman frequency, and require the
> synthesizer to generate 9192 631 772.5 Hz (info
> from a new 5061B manual).
>
> The short HP 5062C runs at 9192 631 774.3 Hz
> with a Zeeman of 70.40 kHz.
>
> Below is a great reply from Corby Dawson about
> the problems this can cause when mixing FTS
> 4050, 4060, HP 5060A, 5061A, 5061B parts.
>
> /tvb
>
> ----- Original Message -----
> > Tom,
> >
> > The zeeman frequency required depends on two things, the magnitude of the
> > C-field current and the synthesizer frequency.
> >
> > HP 5061A and B units that have a synthesizer freq. of 12.6317725 Mhz are
> > configured for a lower value of C-field current by selecting a higher
> > value series resistor on the A15 board. In this case any tube installed
> > (5061A/B 5060 4050 4060) will operate at the 53.53Khz zeeman frequency.
> >
> > HP 5061A and B units and 5060A units that have a synthesizer frequency of
> > 12.6317716 Mhz are configured for a higher C-field current due to a lower
> > value series resistor in the C-field circuit. In this case any installed
> > tube will operate with a 42.82Khz zeeman frequency.
> >
> > Problems arise when synthesizer and or A15 modules are swapped around
> > indiscriminantly leaving a unit with modules that do not match!
> >
> > Since the HP and FTS tubes C-field windings are designed to provide the
> > same field for a given input they are interchangeable. You can operate
> > any of these tubes at a 42.82 or 53.53Khz zeeman. I usually just stick
> > with how the mainframe came configured.
> >
> >
> > I don't remember what I ended up with as far as the zeeman freq. was
> > concerned when I installed a Frequency Electronics tube into a 5061A, but
> > do remember the line width was quite broad in keeping with the reduced
> > accuracy spec. of the FE tubes. (Same spec. as the 5062C tube)
> >
> > I have installed FTS tubes into the 5062C giving it the +-7Z10-12th
> > accuracy spec. and did have to modify the synthesizer for 42.82Khz and
> > set the C-field accordingly.
> >
> > Hope this helps!
> >
> > Corby_
>
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