[time-nuts] Fixing an HP 5370A with a missing ROM board
Mark Sims
holrum at hotmail.com
Sat Jul 25 14:06:54 UTC 2009
Another weakness of the 5370 oven oscillator power supply is the use of a simple zener diode for the oscillator power regulator. The 10811 spec shows a 2e-10 change in freq with a 1% change in oscillator voltage.
Another surprising 10811 spec is the 2e-9 change with 50,000 feet of altitude (call it a 90% change in air pressure, probably more). Barometric pressure here can easily change from say 29 to 31 inches of mercury (call it 5%). If the oscillator sensitivity to air pressure is linear, one could see another 1e-10 change in freq with the weather. Plus the thing is also rather sensitive to humidity (1e-9 over 95% relative humidity). Also a 6e-11 change per degree C.
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