[time-nuts] IC for 1 PPS Output

Robert Atkinson robert.atkinson at genetix.com
Fri Apr 7 08:19:22 EDT 2006

Hi Hans,
Yes the SN74128 will drive a 50R load to TTL levels, it does not however
have a 50R output impedance. The point was made succinctly by Jeroen,
that it is only strictly necessary to terminate one end of a
transmission line at its characteristic impedance, as long as the other
end is perfect. But what is perfect?
Also this is a TTL 5V output, Brooke does not state what he wanted but,
coax is usually associated with sine outputs, Logic pulses tend to be
sent down balanced systems.

Robert G8RPI.

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Hans H. Jucker
Sent: 07 April 2006 10:11
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] IC for 1 PPS Output

Dear Robert

You can either drive from A to B with the world finest German Maybach
or also with a British Mini Cooper. May be the SN74128 50ohms coax-cable
driver is rather matched for this simple application !



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