4 ms·
The HP-5061 Cesium Beam clock (I've repaired a few) frequency modulates the sample frequency just a little bit, using a 137 hertz sine wave. It then compares t
by mikewarot 5y ago
The HP-5061 Cesium Beam clock (I've repaired a few) frequency modulates the sample frequency just a little bit, using a 137 hertz sine wave.
It then compares the phase of the output with the frequency shift.
If the output goes up in phase with the rise in frequency, the frequency is too low.
If the output goes down in phase with the rise in frequency, the frequency is too high.
This signal is used to very slowly pull the 5 Mhz local oscillator into lock with the bandpass of the Cesium beam.
At that point, the output dips on both excursions from zero, a 274 hz "second harmonic" is detected, and this turns on the "Lock" light, letting the user know the standard is now on frequency.
[Edit/More Info]
Here's a link to the Operating and Repair Manual.[1] (PDF)
There is a simplified block diagram on page 35 of the PDF. (Figure 4-1)
1 - http://www.leapsecond.com/museum/hp5061a/5061a.pdf http://www.leapsecond.com/museum/hp5061a/5061a.pdf