On Sat, Mar 16, 2013 at 05:41:11AM -0400, [email protected] wrote: > I've had an "interesting" week or so playing with an X72 and > it turned out not to be quite as straightforward as I first > expected.
> A google based "X72" search of the list archives seems to throw > up more questions than answers so I thought it might help a bit > if I shared what I've learned, whilst hoping others might be > able to fill in some missing gaps for me too :-) > One of the attractions of the X72 was the option to use a 1PPS > input for frequency conditioning, and one of the first things > I learned was that this depends on the firmware version. This > feature was introduced with firmware version 5.02 in 2003, and > this bright and shiny looking just like new X72 turned out to > have 25,000 hours on the clock and firmware version 4.10 from > 2002. Lesson one, looks ain't everything :-( Did you open up the unit completely? If so, did/could you take/make some photos/scans of the electronics/components? best, Herbert > Next problem, these are specified at shipment to have > an accuracy of <+/-5E-11 but obviously they age. Whilst > Symmetricom does offer analogue and digital options for > adjustment, more of which in a moment, there's no user > option to properly adjust the startup frequency, as in the > FE5680A for example, instead there's a flag that gets set to > conveniently warn the user when it's time to send their X72 > back to Symmetricom for a "service". As received, the locked > output frequency of this unit was 9.999,999,986,xx Mhz, the > xx indicating digits still wandering after lock which may > reflect more on the less than ideal antenna placement for the > Thunderbolt providing the counter reference. > When finally in a negotiated position to remove the "do not > remove" warranty stickers both were found to cover access > holes, one of which led nowhere but the other to a trimmer > capacitor adjacent to the lamp assembly. > Whether or not it was the intended purpose this did allow > adjustment of the output frequency, unfortunately it ran out of > steam at 9.999,999,992,xx MHz so was reset to where it started. > There are two further options for frequency adjustment, not > including the digitally adjustable CMOS outputs, one is a > software command that allows an offset to be specified, based > on the free running frequency and in steps of 2E-12, which > does allow for reasonable adjustment relative to the startup > frequency but resets every time power is removed > The other is an anologue control input which can be varied from > 0 to 5 volts and allows adjustment to a few parts in 10^11, but > which sits at just over 4 volts to bring this one to 10MHz. > _______________________________________________ > 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.
