[time-nuts] FE-5680A arrived
lists at rtty.us
Wed Jan 11 21:05:45 EST 2012
They have a VCXO in the loop. It probably does not have much over +/- 50 Hz of useful range.
On Jan 11, 2012, at 8:32 PM, GandalfG8 at aol.com wrote:
> My observations are that the RS232 offset on these needs to be considered
> as very much a fine adjustment only, and presumably just intended to pull
> the frequency on to 10 MHz rather than to provide a usable offset.
> I did try pushing my first unit to the extremes of the adjustment range
> shown in the manual and it didn't like it, the frequency was highly unstable
> and at one extreme it just gave up and rejected the offset.
> Observations on three units so far indicate that none seem to have had any
> offset programmed in the field but all are less stable the further they are
> from being set to 10MHz.
> I haven't recorded any long term data as yet, just observed the short term
> stability on an HP 53132A and Tek FCA3100 clocked against one of three
> T'bolts, but am getting a definite impression that 10MHz is a sweet spot and
> that anything either side is just begging to be corrected:-)
> In a message dated 12/01/2012 01:04:03 GMT Standard Time, smither at c-c-i.com
> More observations. My unit is S/N 0316 61953, UN 63983. If I try to
> change the
> offset count (using RS232) by more than about 131,000 counts (0x20000) at
> a time
> it sometimes loses the 1PPS and the lock signal goes high.
> By bringing the offset count up slowly (increments of 0x10000) I recorded
> following drift rates versus offset count:
> 0 usec / sec at 0
> 1 usec / sec at 1441792 (0x160000)
> 2 usec / sec at 2949120 (0x2D0000)
> 3 usec / sec at 4390912 (0x430000)
> 4 usec / sec at 5898240 (0x5A0000)
> The offset count was incremented in units of 0x10000 (65,536) counts so the
> drifts are approximate.
> A plot of these results is here:
> My unit appears to have an adjustment resolution of about 6.8E-13 / count -
> close to what has been reported here before.
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