[time-nuts] Trimble Thunderbolt 1pps
Hal Murray
hmurray at megapathdsl.net
Fri Jan 3 20:09:38 EST 2014
saidjack at aol.com said:
> Your plots don't show the wave being reflected by the cable end, and
> bouncing back and forth.. Until settling down.
Yes. I'll put up some nasty pictures if anybody wants an ugly example.
For that set of graphs, I tried to get rid of that sort of junk. I was
working on the bench, using connectors and clipleads rather than PCBs or
soldering whatever so things could be (much?) cleaner.
For the coax, there was a short chunk of coax from the TBolt to a Tee at the
scope, then the long chunk of coax under test, then a 50 ohm terminator at
the other scope input. You can see some ringing due to the coax not really
matching the terminator.
For the twisted pairs, I used clipleads. The first/simple try wasn't good
enough. The non-twisted cliplead wires were long enough to cause visible
cruft. I ended up with a BNC to cliplead adapter with wires that were only 6
inches long.
At the far end, I had a resistor merged into the clipleads, and adjusted it
for best results.
For the Cat-5 and Cat-6, I used a pair of RJ-45 to DB-9 adapters without the
DB-9 connector. The wires coming out of the adapers are about 2 inches long.
I forget what I did for the RG-6 which is 75 ohms. I have a pair of 50-75
adapters, but I don't remember doing any scaling to get the graphs to come
out right and I don't see anything in the gnuplot commands to make the
graphs. So I probably use a cliplead setup like for the twisted pairs.
--
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