[time-nuts] HP5061B Versus HP5071 Cesium Line Frequencies
kb8tq at n1k.org
Fri Jun 2 08:57:10 EDT 2017
> On Jun 1, 2017, at 10:04 PM, Donald E. Pauly <trojancowboy at gmail.com> wrote:
> The lock system on the HP5071 is complex and expensive. My plan to
> improve the HP5061B is to to use a pair of third overtone crystals
> running at 91.9 mc and 100 mc. I have come up with the magic numbers
> to lock them together. This eliminates all multipliers with the
> exception of the A4 board. The 12.61 mc synthesizer input presently
> wastes half the microwave power produced by the 90 mc input in the
> unused lower sideband. Therefore only half the 91.9 mc drive is
> Eight bit ECL dividers in one package are available to perform the
> necessary lock. When multiplied by 100 to the cesium resonance line,
> the 91.9 mc frequency is a few cycles high so that C field currents
> are reasonable. With crystal cuts for zero temperature coefficient at
> 25°C, it is possible to get along without an oven. Room temperature
> performance at 25°C±5°C is ±15·10^-9.
I would suggest you check a few real crystals over the 20 to 40C range ….
With all the “stuff” in a 5061, it will change (rise) at least 10C after turn on.
> Oscillator warm up time would
> be measured in seconds.
> Square wave modulation of variable frequency and amplitude shows
> promise for reducing the noise effects of the beam tube. You can
> smoothly change the lock time constant, deviation and frequency. This
> would avoid the big disturbance of the HP5061B when you switch from
> OPR to LTC. (OPR=operate with 1 second time constant, LTC=operate with
> 100 second time constant)
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