[time-nuts] Thunderbolt PPS output

Didier Juges didier at cox.net
Sat Aug 9 19:14:59 EDT 2008

The TB's PPS output has something like 5 ohm output impedance. It is very
desirable to terminate the coax cable with 50 ohm at the other end,
otherwise you will get endless ringing

The following web page uses the PPS output of the Thunderbolt to illustrate
ringing in a non-matched cable:


And this page shows a minimum, energy efficient pulse stretcher:


Didier KO4BB

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Scott Mace
> Sent: Saturday, August 09, 2008 5:41 PM
> To: Discussion of precise time and frequency measurement
> Subject: [time-nuts] Thunderbolt PPS output
> Has anyone used the thunderbolt PPS output with a N8UR 
> FatPPS?  I'm seeing a large (+-100-300us) amount of jitter on 
> the output of the FatPPS.  This same setup works fine with 
> the input from z3801a (using a PECL/TTL converter) or the 
> Fury (even though the Fury's pulse is wide enough to begin with).
> Is there something special about the thunderbolt PPS output?  
> I noticed it seemed to require 50ohm termination to get a 
> clean signal when I connected it to a counter (5334a) with a 
> 3 foot cable.
> I'm using the FatPPS in conjunction with a soekris 4501 with 
> the tmrin mod.
> 	Scott
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