[time-nuts] HP5359A non-linearities

Magnus Danielson magnus at rubidium.dyndns.org
Mon Dec 17 19:45:59 EST 2007


From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
Subject: Re: [time-nuts] HP5359A non-linearities
Date: Tue, 18 Dec 2007 00:28:34 +0000
Message-ID: <13318.1197937714 at critter.freebsd.dk>

> In message <20071218.004912.692035820.cfmd at bredband.net>, Magnus Danielson writes:
> >Fellow time-nuts!
> >
> >I have been making some measurements on the HP5359A using the DTS2070C.
> >I am adjusting the period and measure that.
> >
> >Initially it is apparent that the HP5359A does not hit the mark, 
> 
> The 5359A doesn't work quite the way you would expect, the trigger
> is just sort of a trigger for an internal trigger, from which the
> pulse will be delivered, very precisely (if properly calibrated).
> 
> It's kind of strange, once you've read their explanation, it makes
> sense.

I have spent my time over the operating and service manual to figure it out, so
I have a fair idea of how it ticks, and when operating in the frequency/period
mode it triggers itself. What I have been doing is measuring the acheived
period time vs. "dialed" period time.

The startable VCO is indeed a strange beast, but it makes kind of sense.
You don't know when the trigger gets there, but once it does, you want to
count some number of 129/128 * 10 ns clocks and then analogue interpolate the
last fractional 129/128 * 10 ns in about 50 ps steps, or about 1/200 fraction
of that. It is very similar to the startable VCO in the 5370B, but with a
different ratio (257/256).

You could use some other method than the startable oscillator, but all methods
depend upon some means of measuing the trigger error relative some stable
clock and then maintain that allignment error somehow while adding some
arbitrary programable delay value to output an output event.

Regardless of method, we can expect a variance of jitter and variance of step-
size/non-linearity. I was kind of interested in verifying the properties before
using it to test lesser counters than the DTS-2070C. ;-) Normal time-nut
activity I guess.

Cheers,
Magnus



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