Hi The interesting part is that the LPRO sweeps *much* slower than the FE. For what ever reason, the FE spends most of it's sweep cycle with the VCXO going nowhere (railed at one end or the other).
Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Rex Sent: Tuesday, February 14, 2012 6:11 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] FE-5680A Question The Efrotoms (FRS-C. Lpro) find the lock by modulating the microwave frequency with an audio signal (127 Hz if I remember right) which causes the light sense modulated signal to double in frequency when centered on the hyperfine frequency. See the manuals for nice description. The 5680A seems to accomplish the same thing by stepping the frequency +/- 700 Hz rather than mixing in modulation. Never saw any documentation on that, but seems to be implied by the great hacking Javier Herrero has done on the loop frequencies. Seems to me that finding lock, that is finding the dip, may be a bit harder with the stepping than with the modulation. Maybe the observed drop in frequency during start up is part of the algorithm to walk the stepped frequency to center on the hyperfine light transmission dip. On 2/13/2012 4:39 PM, Bob Camp wrote: > Hi > > If they are looking for a pattern what is the pattern? > > Bob > > > > On Feb 13, 2012, at 3:35 PM, paul swed<[email protected]> wrote: > >> The reason to sweep low is to establish a particular lock pattern to look >> for. >> Check the programmed offset before retuning. Mine was at mid range 0000 >> Search the threads for sending commands to the FE5680. >> >> On Mon, Feb 13, 2012 at 2:56 PM, Bob Camp<[email protected]> wrote: >> >>> Hi >>> >>> For what ever reason, most of the FE's sweep down to about 200 to 250 Hz >>> low. Few sweep more than 50 Hz high. I have one unit that locks fine and >>> only sweeps 5 Hz high. >>> >>> Yes, I would open it up and re-tune. I think I would only bump it about 50 >>> Hz or so. I have no idea *why* they are all tuned low, but there may be a >>> reason (like avoiding a false lock). >>> >>> Bob >>> _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
