On 07/02/14 20:40, beale wrote:
The entry in the FE5680 FAQ on this subject may be helpful, if you haven't
tried it already.
http://ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5680a_faq#what_if_my_5680a_output_does_not_lock_up_after_several_minutes
I have 3 of those units; one did not lock until I adjusted the trim-cap C217 to
bring the free-running frequency of the oscillator into range. If you have a
reasonably accurate counter you can check if this is the problem or not by
seeing if the output frequency (which ramps up and down prior to lock) crosses
through 10.000000 MHz or not. Mine did not.
This is why an oscillator trim is required. The oscillators offset is
outside the lock-in range, DDS offset trim can possibly, for the DDS
feedback version, cause lock-up, but the output won't be 10 MHz. This
can naturally be used as a feature to have neat beat-frequencies in a
DMTD setup, but otherwise not really recommended.
Good that you have tried it and could point to the C217 trim-cap.
Hopefully Jim can use that.
Jim, do you have a GPSDO around? If so, use a counter and try to see
what the top and bottom values in the sweeps are, adjust C217 so that
the sweep range covers the 10 MHz line. Make sure you trim it with some
margin to the edge of the sweep-range. Now, you should also be able to
monitor how it locks up.
Cheers,
Magnus
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