[time-nuts] WWVB phase modulation test April 15-16

Hal Murray hmurray at megapathdsl.net
Thu Apr 12 03:56:23 EDT 2012


> Just the T and a DC block. 1/4 wave at 60 kHz is far, far longer than any
> cable you have. 

This is time-nuts.  Somebody is likely to do something most of us would 
consider, well, nutty.

It's probably reasonable to make a lumped-circuit approximation of a long 
transmission line at 60 KHz or 100 KHz.

Many years ago, when we were working on early 10 Mb Ethernet, a friend rigged 
up a good approximation to a long chunk of coax with 1 R and 1 C and a few 
clip leads.  It looked pretty good on a scope.

I ordered several 500 ft spools of coax so we could test the real thing.  500 
ft of Ethernet coax (not thinwire) is a serious spool.  A key step was 
getting the maintainance guy to build a dolly with serious casters.  He was 
happy to do something strange.  The result was slight overkill which is what 
I wanted.  It worked great.  Every lab should have one.  :)

How many of you have used the Tek scope-probe to BNC adapter?  I tried a bit 
but couldn't find anything on the web.  The idea was (roughly) that you put a 
BNC Tee in the line you wanted to watch and this magic gizmo on the Tee.  One 
end was BNC.  The other end was a hole where you inserted a scope probe.  The 
idea was to avoid the inductance on the pigtail for the ground cliplead.

----------

Not quite so many years ago, we built a SONET/OC-3 delay box.  It was just a 
fiber optic receiver, FPGA, knobs, memory, and fiber optic transmitter.  The 
FPGA could just barely  run at 155 megabits.  We used a recycled memory 
module.  I think it was 36 bits wide with 1 megabit chips.  The idea was to 
let the software guys test long links in their lab.  It worked great.  (I 
think that size memory covered (roughly) California to Paris.)


-- 
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