[time-nuts] 5370 Time interval calibrator.

SAIDJACK at aol.com SAIDJACK at aol.com
Mon Jun 11 07:18:52 EDT 2007

In a message dated 6/11/2007 01:19:56 Pacific Daylight Time,  
robert.atkinson at genetix.com writes:

>It's  on my list to build one. I was going to use a 4 port "transfer"
>type  coaxial relay to do the start-stop swap, this should have even
>better  balance than the Omron and PCB tracks, and has direct SMA  output
>connectors. The HP unit also has an HPIB control for automatic  use but
>this is optional. It's discrete logic so even that could be  copied.

>Robert G8RPI.

Hi Robert, Bruce, Didier, Tom, etc,
so I finally went ahead and played with the pots. Ok, to make a long story  
short, I was able to reduce my RMS jitter from >50ps to <20ps :)
First, I checked the INT and EXT 10MHz test points, both had about 20ps and  
15ps jitter. So for sure the 10811 is good (not quite as good as the external  
Fury, and this can be seen in the unit's measurement results as well).
Then I adjusted the DAC voltages. Not a big deal. Within 500 microvolts  now. 
They were off by about 2 - 4mV, within spec.
Then I started with the multiplier board. I started at 10pm, it's now 4am  
(and I gotta go to work soon!)
Wow. That was tough. My suggestion to anyone: Connect your Spectrum  analyzer 
to the 200MHz test point, and VERY Carefully (!) adjust from right to  left 
so that all spurs are gone. The pots all interact, so this is quite tough  to 
After all spurs are completely gone, adjust the left most (last) cap  trimmer 
for best RMS jitter performance.
While you are doing that, also adjust the trigger pots (both) for best  
I can now get 17 - 20ps RMS 100 samples or 1K samples. But I have to set  the 
trimpots just right. I started with 100ps, not a bad result.
Next up will be to adjust the trimpot for the Preset setting so that I get  
best performance in PRESET mode. That's kind of tough, I haven't located those  
pots yet.
It took 6 hours to get the settings right.
Lastly I will investigate using a low-noise, low-spur 200MHz VCXO to  
clean-up the Analog multiplier output, since it seems the 10/50MHz spurs are  what 
are causing the jitter. A very clean 200MHz Crystal locked with a slow loop  
filter using an Exor gate should do the trick to get rid of all spurs.
I don't think I will touch the interpolator adjustments.
Thanks again everyone!

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