[time-nuts] FE5680A signal output

wje wje at quackers.net
Fri Jul 11 13:18:48 EDT 2008

If I remember correctly, the 1PPS pulse width is only about 100 ns.
There are two possibilities:

1) you can't see the pulse height properly at the very low sweep rate 
you're using. Trigger on it at a much higher sweep rate, crank up the 
intensity on your scope, and look carefully.

2) the output is dead. This happens occasionally. I had to replace the 
74ac240 buffer in mine.

Bill Ezell
They said 'Windows or better'
so I used Linux.

Remco den Besten wrote:
> I recently obtained a FEI FE-5680A Rb standard Revision: B.
> After powering it up 'out of the box', a lock @ 50.25505.. MHz was obtained
> within
> a few minutes, confirmed by measuring the lock indicator on pin 3 of J1 and
> listening to the signal on my FT 857 receiver. Nice to hear it sweeping
> before locking ;-)
> Here te levels at pin3 of J1 are: unlocked +4V, locked +1.5V
> A 1PPS signal could not be detected with a multimeter, so I connected a
> scope.
> I consider the signal levels somewhat peculiar and am curious if FE 5680A
> owners
> here have the same experience. E.g. the amplitude of the PPS signal at pin6
> is superimposed on a DC offset of ca. 170 mV and amounts (only?) 25 mV.
> It is visible as a small spike here (depending upon the time base of 
> course).
> My perception of a '1PPS' signal is a signal with TTL levels or open
> collector out or something, and a pulse width of 10 - 200 ms..
> I connected a 2k2 resistor between pin6 and pin1 (pull up) but could not see
> any improvement. The top-top amplitude remained ca. 25 mV.
> Pin6 (measured with scope) spikes with t = 1 sec:
> 200mV       |      |      |
> 170mV ------|------|------|
> The signal above will be hard to interface, but I feel that perhaps the PPS
> output is not 'set' or perhaps broken.
> After powering up, the unit draws 1.6A which gradually decreases to 800mA.
> This looks normal.
> Anyone any ideas?
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