[time-nuts] HP 5370B jitter

[Magnus Danielson]

From: SAIDJACK at aol.com
Subject: Re: [time-nuts] HP 5370B jitter
Date: Fri, 13 Jul 2007 17:16:38 EDT
Message-ID: <d48.c9234d4.33c945b6 at aol.com>

Said,

Returning to this message...

> I sent spectrum plots of the 10MHz 5370B output to this list earlier, the  
> output is very sad. It's extremely dirty and jittery (well, compared to the 4ps  
> noise you got, and compared to what the 10811 can deliver).

Further investigations have now shown that the 10811 output is clean, just a
little 3rd harmonic but nothing to worry about. The INT test point is also
clean. I suspect the output drive part, as other outputs to various parts are
also free of the 5 MHz. The 10 MHz present detector circuit is currently my
main suspect. It consists of a "one-shot multi-vibrator triggered by the 10 MHz
signal". Having a RC time-constant of 100 ns makes it a suspect indeed. Probing
it (pin 11 on A8U1) clearly shows a waveform wich looks like a 25% 5 MHz with
a short spike on it. This little culprit of a detector is infact a wideband
comb-generator which contributes its 5 MHz as sidebands to the output 10 MHz.
It's only purpose in life is to light a LED only visible to the servicing
engineer (me in this case). Thus, making a small modification to disable it
during normal operation would improve the quality of the 10 MHz output
considerably if I am right. Since I don't do ECL design on a daily basis, I
will have to ponder a bit in order to come up with a good method of acheiving
this.

> After calibration to 4ps, what does your 5370B unit read for it's  internal 
> RMS noise now?

Self-reference from 10 MHz output gives 29.9-34.0 ps.
A 130 MHz +15 dBm sine results in readings in the 35-41 ps range.
A 5 MHz +15 dBm sine from the Cesium does not acheive as deep levels, but
reaches 39-43 ps but does not vary as much.
A 10 MHz from anther 10811 source reaches 37-43 ps.

All measures where taken in TI mode, +/- TI, StdDev for 1k samples.
Optimum 1M/50 Ohm termination strategy selected for each signal. Flipping the
input termination switches for both channels quickly creates different levels
of input jitter.

I have not trimmed anything but the multiplier stage.

I have tested running frequency measurements and up to about 130 MHz seems
safe. At 133 MHz it will start to false-trigger and at 134 MHz it is just
starting to make obvious errors and at higher numbers it gives nonsense
readings.

I might add that I have only trimmed the 200 MHz multiplier chain so far.

Cheers,
Magnus