[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.


-- 
These are my opinions.  I hate spam.





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