[time-nuts] time stamping counters

Pete peterawson at earthlink.net
Wed Jan 2 20:58:44 EST 2008


Magnus,

I was unable to respond to your message earlier; too many visitors
& too many diversions.

Thanks for the info on the CNT-91; I have read the datasheet
thoroughly and it would be VERY nice to own one, but too
many $$ for me.

I have downloaded the evaluation copy of Timeview. It works
well, but without any capability to save/store results, it's only
a toy for me. I can't justify the $395 license fee since I'm retired.
Oh, well.

I have a licensed copy of HP VEE 5.0 (now quite old), but it
does allow me to operate my CNT-81 from GPIB and save
data for later processing. Using the internal (block) function
I have been able to capture TI data at 6Kpoints/sec, but records
have to be limited to 4466 points per capture. Still, this is 
useful.

While learning to use my CNT-81 I was surprised to discover
a minor, but possibly important anomaly in it's performance.
I was attempting to discover the best case jitter measurements
which could be taken on stable sources at 5, 10 and 100MHz.
For the 5 & 10 MHz sources, the jitter consistently reads <
22ps for large & small samples. At 100MHz I was expecting
jitter results as good, or better than those at lower frequencies.
But, this was not the case. The jitter results were >40ps!
After consulting the folks at Pendulum, it was confirmed that
input signals near the internal 100MHz reference cause
period measurements to exhibit 240ps peak-to-peak jitter at
10x the frequency delta of the reference to the input. I have
screen shots of Timeview analysis if you're interested.

Regards,
Pete



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