[time-nuts] Why are 1PPS signals so skinny?

[Hal Murray]

SAIDJACK at aol.com said:
> Also, the Thunderbolt has less than 5 Ohms output impedance, so you  get a
> reflection going back from the 50 Ohms end-termination anyway because the
> impedance is mismatched! 

I think that's a different problem.

If the far end termination matches the cable there won't be any reflection.

If the far end isn't terminated correctly, there will be reflections from the 
far end.  There may also be reflections from joints in cables or a Tee and 
input load if you are daisy chaining multiple instruments.  When those 
reflections get back to the typical low impedance driver, they will get 
reflected back again.

It's not uncommon to use both source/series and end/parallel terminations.  The series terminator drops the signal level by 2 but minimizes reflections if you are working in a less than ideal setup.  It also provides a current limit on the driver in case something gets shorted.


-- 
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