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<paulsw...@gmail.com> 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<li...@rtty.us> 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
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