[time-nuts] Re: Symmetricom/Datum FTS-1050A Disciplined Frequency Standard

[ed breya]

That's an interesting old machine - very cool.

One thing though, is that unless I'm missing something, I believe the 
two available loop time constants are in minutes, not seconds, or that 
it should be in many more (maybe 100X) seconds, if stated that way. 
Since the unit can synchronize to a 1 PPS reference, it would make sense 
that the loop filtering goes way beyond 1 or 100 seconds.

If this is the case, then there's some typo errors in the manual.

As far as I know, time constant is still T=RC, or megohms X uF = 
seconds, in the convenient short form I always remember. So, the long 
time constant setting of 2500 megs by 10 uF gives 25,000 seconds - over 
400 minutes. Now, I can picture it being defined also by the scaling of 
the tuning range used. If you take the input divider 100 k/ 10 k, times 
the amplifier gain a little less than 2, that gets it overall into the 
100 minutes ballpark. The filter is not an integrator in the pure sense, 
but an RC LPF, so the output is bounded to about 20% of the "stored" 
tuning voltage from the DAC system.

Regardless of how you estimate, it seems like the times have to be in 
minutes, not seconds.

Ed