[time-nuts] Why using HP5370 ext-ref is (maybe) a bad idea

GandalfG8 at aol.com GandalfG8 at aol.com
Mon Mar 3 09:08:22 EST 2014

What about replacing the 3336 external reference with something like an HP  
10811 and checking what difference, if any, that makes?
In a message dated 03/03/2014 13:42:33 GMT Standard Time,  
phk at phk.freebsd.dk writes:

In  message <C542ADEE-19DD-4DAB-A1BF-FB842C0775FB at rtty.us>, Bob Camp  

>The likely answer is that the trigger point must be  changing.

Yes that would be my first theory as well.

> The  question is whether it's changing because the 
>3336 is doing something  (small waveform changes) or because the 5370 is 
>doing something.  

Yes, and obviously there are many experiments that can be  performed
to flesh out the details of that:

Changing the 3336 output  amplitude.

Exchanging the signals, so the 3336 feeds ext-ref,
and  lab-standard feeds start+stop.

Using a different  lab-standard.

Measuring opposite polarity etc.

>I would make  up / dig up a coax cable that is 8 degrees at 10 MHz. 
>Something around  1/2 meter long should do the job. 

As I said, I'm not really kitted out  for RF work, so my selection
of coax isn't that versatile and I don't have  the crimp-tools or
routine to make my own.

>Next step would be  some sort of filtering between the 3336 and the 5370. 
>That would help  rule out harmonics and spurs from the generator as the 
>source of the  problem.

The 3336 delivers pretty clean output, so I expect a couple of  sanity
checks will exonerate it.

Unfortunately my HP33120 does not  have an external clock input, so I
can't use that for the experiment.   Anybody with a HP3325 or later
HP33* with an external clock input can  participate in this game...

But to be honest, I'm not sure how much  more work is really warranted
for me, given that I don't think I can tune  the 200MHz multipliers
filters much better than they presently  are.

The really interesting experiments, in my mind, would be to ditch  the
200MHz multiplier and feed 200MHz from a good generator with  high
purity instead.

But then again:  It is so much easier to  just run the HP5370 on the
internal clock and that solve^H^H^H^H^Hhides all  the problems.

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