[time-nuts] HP5061B Cesium Tube Resonance

Donald E. Pauly trojancowboy at gmail.com
Fri Apr 21 18:26:58 EDT 2017


Yesterday we swept our HP5061B thru the cesium resonance curve.  As
far as I know this is the first time that the curves have been
published.  The original phase modulation is a very unlinear sine wave
frequency sweep.  We built a 100 ms time constant integrator for the
20 cps triangle from the function generator.  When a triangle is
integrated, the result looks much like a sine wave but it is not.  It
is really back to back parabolas as shown in
http://gonascent.com/papers/hp/hp5061/waveform/dblepara.jpg . The
waveform is actually inverted in the display.  Note that it appears a
bit squashed.  That small difference results in a linear triangle
frequency sweep. We drove J1 on the A3 board with the output of the
integrator and turned R20 the Mod Level pot all the way up.  The phase
modulation differentiates the output of the integrator to restore
linear sweep.

We ran the electron multiplier output J1 which went into the A7 board
into scope channel two see
http://gonascent.com/papers/hp/hp5061/waveform/csweep.jpg   Vertical
was 5 millivolts per division inverted.  Ground is shown by the yellow
1 arrow and the scope amplifier was providing the 1 MΩ termination.
The corresponding peak beam current is 20 nA or 20 on the HP meter.
Because of the varactor polarity, the frequency sweep is inverted and
is from -1,200 cps below resonance to +1,200 cps above resonance.  The
center of the negative going sweep of the triangle is the peak
response of the cesium tube while being swept from low to high
frequency.  At -550 cps below it and +550 cps above it are seen the
two valleys of the main resonance peak.  The center of the positive
going sweep of the triangle is also the peak response of the cesium
tube while being sweep from high to low frequency.  The valleys either
side of the main peak are seen again along with partial false peaks.

As you approach the positive peak of the triangle the lower false peak
is seen.  As you approach the negative peak of the triangle, the upper
false peak is seen.  Integrator limitations kept us from having enough
drive levels to see the complete lower and upper false peaks.
Remember that the sweep is reversed at both peaks of the triangle, low
to high and high to low.  See the artists depiction at Figure 4-43 in
the manual.


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