[time-nuts] 5370B practical question

Christophe Huygens christophe.huygens at cs.kuleuven.ac.be
Sat Feb 2 06:44:46 EST 2008


Hi,

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,
Christophe






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