[time-nuts] HP5061B Modulation Adjustment

Bob kb8tq kb8tq at n1k.org
Wed May 17 07:05:37 EDT 2017


> On May 16, 2017, at 10:04 PM, Donald E. Pauly <trojancowboy at gmail.com> wrote:
> https://www.febo.com/pipermail/time-nuts/2017-May/105298.html
> We recently got our second HP5061B to lock after changing the beam
> tube. We did no alignment with the exception of changing the gain on
> Beam current.  Ion current dropped from 14 to 1 with only a few hours
> of operation of the instrument.  We obtained momentary lock but lost
> it after a couple of minutes.  The trouble was a blown themal fuse on
> the HP10811 oscillator which shut down the oven.  We have TEMPORARILY
> jumpered it while the correct fuse is on order.
> We aligned the C Field on #1 but have not done that alignment on #2 yet.
> The 5 mc output of our #1 instrument was compared to the 5mc output of
> #2 with an HP10514A balanced mixer. Two input ports L and R are
> multiplied by internal Shottky diodes to produce an X output which can
> be terminated in 50 Ω. Maximum input current on both the L and R port
> is 40 mA or 2 V rms.   One instrument was put in Open Loop and the
> fine frequency adjusted to approach quadrature. It was then returned
> to OPR and steered to final quadrature with the C Field.
> We used a digital voltmeter with a resolution of 10 uV dc to measure
> the X output of the mixer with the L and R inputs in near quadrature.
> The mixer output contains a large 10 mc component of about 2 V peak of
> peak which rides on the dc representing the phase difference. The dc
> output for in phase and out of phase inputs is about +1 and -1 Volts.
> Our calculated sensitivity was 31 uV per picosecond of error when
> within a few degrees of quadrature. Lock within a few picoseconds was
> obtained by adjusting C field on #2.  It had to be continuously
> manually steered.  We could not look at the X output on the scope
> because of the large rf level present.  Our digital meter might have
> been experiencing rf overload causing inaccuracy at low dc voltages.

Keep in mind that the mixer has millivolt level offsets and millivolt level
drift (over a wide range). 

> Continuous lock was lost a few times on #2 which we attributed to it
> needing a complete alignment.  Second harmonic was only 22.  

There is a gain pot that “sets” the second harmonic. It can be low and the 
device will still lock. 


> The
> procedure in 5-217 g for modulation adjustment is not very scientific.
> It calls for adjusting modulation for maximum 137 cps out of the AC
> amplifier board when the beam tube is driven at 5x10^-9 below the
> resonance line.  Modulation is then to be reduced by 5%.  This affects
> all other adjustments.
> We decided to directly measure this deviation with precision.  The
> phase noise of the 90 mc output of the A3 multiplier board was
> measured as well as the modulation.  The spectral width of our
> function generators at 5 mc was compared to the HP5061B 5 mc output.
> Our adventures with this project will be covered in a separate post.
> πθ°μΩω±√·Γλ
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