[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.)

These are my opinions, not necessarily my employer's.  I hate spam.

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