[time-nuts] Fwd: OT: 10 MHz data capture, help
ed_palmer at sasktel.net
Sat Apr 11 20:41:46 UTC 2009
The Agilent web site has most of the manuals for the 5372a. The data
sheet and the "Condensed Specification & Reference Guide" (over 100
pages!) gives you most of the functionality.
The 5372a's biggest deficiencies for a time nut are its resolution of
only 150ps and its maximum built-in timing period of 8 seconds. This
means that even though it can calculate Allan Deviation, it's limited to
about 1.5e-10 @ 1 sec. and it can't calculate anything beyond a tau of 8
seconds. You have to use external means to improve the noise floor
(e.g. mixers). The 8 second limitation can be sidestepped if you use
GPIB to pull the data and process it externally.
The 13M readings per second that Magnus mentioned is limited to
measuring the period of the incoming signal and then incrementing a
count of how many measurements were in that range. There are 2000
'bins' that can be as small as 200ps wide. No time stamping, no
calculations, just how many measurements were in that range. Useful
but, at the same time, limited. I recently used it to collect 100M
measurements of the 10 MHz output of a Navsync GPS receiver. I was able
to infer the algorithm that they used to keep the output on frequency.
If I remember correctly, it took less than 20 seconds to collect and
plot the data!
SAIDJACK at aol.com wrote:
> Hi Magnus,
> thanks for the info, I got to look at that 5372A again. They were too costly
> when I last checked it out some time ago.
> There are several Wavecrest on Ebay, starting at ~$1200 for a working unit..
> I would love to get my hand on a CNT-90, but again cost and availability is
> an issue.
> In a message dated 4/11/2009 07:44:40 Pacific Daylight Time,
> magnus at rubidium.dyndns.org writes:
> No. The HP5372A happily gives you a rate at 13,3 MHz sample rate. I
> think the SIA-3000 is higher than 40k too (I think I recall 200k) and I
> know that the Pendulum CNT-90 and followers also passes that rate.
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