[time-nuts] 5370B practical question
didier at cox.net
Sat Feb 2 10:13:00 EST 2008
I am sure it can't have anything to do with it ;-) but the 5370B is only
specified to 100 MHz.
My 5370A stops working around that frequency.
Try simply dividing the frequency by two and see what happens, or mix it
down just enough with a stable oscillator so that the IF is below 100MHz and
the image is well rejected.
I have a clean (if not time-nuts quality) DIP crystal oscillator at 64 MHz
that I use for that kind of experiments.
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Christophe Huygens
> Sent: Saturday, February 02, 2008 5:45 AM
> To: Discussion of precise time and frequency measurement
> Subject: [time-nuts] 5370B practical question
> I am trying to start some Allen Deviation measurements on
> some VCXOs I have built those for 117, 106.5 and 123MHz
> (amateur radio use). The phase noise it not my primary
> concern (for now) but short term stability is (systems are
> locked to GPS etc). I would like to more formally
> characterize the performance hence my interest in AD.
> I am using the 5370B. For the moment, to get my feet wet, I
> am just measuring frequency - I don t want to deal with TI
> yet. I think I understand the limitations of both the method
> used and the counter.
> Upon measuring the 106.5MHz results are more or less as
> expected: I see excursions around center of +/- 20milliHz...
> (1second measurement time) I think these are due to hitting
> the frequency performance limit of the instrument.
> But at 123.5MHz, about 1 in 5 measurments, there is a 1Hz
> jump... the instrument showing 122.999998005 in stead of
> 999005. I never notice 100, 500 mHz jumps, only +/-20 and
> (+/-20 - 1000).
> I don t know much about the internals... is this the counter
> hitting the 100MHz limit, is something broken, or not likely
> is my VCO jumping by 1Hz?
> Thanks for any insight,
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