[ntp:questions] Very large jitter and offsets on GPS ref clock after upgrade to "p5"

John Hasler jhasler at newsguy.com
Mon Jan 9 00:27:56 UTC 2012


David Woolley writes:
> If you want fast edges to be reproduced accurately, you must do, as
> Unruh says, and terminate the line with its characteristic impedance.

But RS232 drivers won't reliably drive 100 ohm loads.  Another possible
problem with RS232 on long runs is 60Hz interference due to ground
loops.  As you suggest, it's best to use 422 for long runs.

If you must use RS232 drive the cable with +-15 from a 100 ohm source.
It is not necessary to terminate the cable with its characteristic
impedance at both ends.
-- 
John Hasler 
jhasler at newsguy.com
Dancing Horse Hill
Elmwood, WI USA



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