[time-nuts] FE-5680A Voltage tolerance

beale beale at bealecorner.com
Thu Jan 19 18:56:57 EST 2012

Very interesting data. I wonder if this has to do with the nominal center frequency of the internal 60 MHz VCXO (which is divided by 6 to generate the 10 MHz output).  On my units, the center frequency is pretty low and the 10 MHz output is near the top of the range (actually beyond the range on one unit, so it would never lock, until I tweaked the C217 trimmer). If there's an internal supply rail that sags even slightly, that would probably put at least one of my units out of lock range.  

Of course there's more to the whole system, maybe the Rb doesn't reach temperature, or the microwave section droops or has inadequate power level, etc.  I'd suspect even if the unit does work at very low voltages, it is more marginal, noisy and less stable.  It is surprising that it works at all below 11 V input, though.

-John Beale

>  From: gonzo . <cadbloke at hotmail.com>
>  Subject: [time-nuts] FE-5680A Voltage tolerance
>  Experiment for the day.
>  I thought I'd follow Dons quote and see how tolerant my unit is.
>  My benchmark is at 15.5V it locks in about 3min.
>  I backed off the supply to 10.8V and the lock time (from cold) is 8min.

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