[time-nuts] Buffering the 1pps output from a Z3801A

[Didier Juges]

The Thunderbolt's output impedance on the PPS output is much less than 50
ohms, more like 5 ohms.

If you terminate the other end of the cable with a good 50 ohms termination,
you will be OK, even though it would be better to put a ~47 ohms series
resistor right at the TB output before driving the cable. This will reduce
the available amplitude, but will reduce ringing even more.

Check this page:

http://www.ko4bb.com/Test_Equipment/CoaxCableMatching.html

I used the PPS output of the Thunderbolt as a fast rise time pulse generator
for cable matching/reflections experiments.

It will show you what to expect when you use that output to drive a long
cable. 

Didier KO4BB

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Dave Brown
> Sent: Wednesday, March 26, 2008 2:57 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Buffering the 1pps output from a Z3801A
> 
> Peter
> All comments so far relate only to the Z3801A. The Trimble 
> Thunderbolt has a TTL level 1 pps 10 uSec pulse output on a 
> BNC connector intended to be loaded with 50 ohms.  AFAIK 
> there is no ECL level pps output available from the 
> Thunderbolt via its 9 pin serial port connector. 
> It's cetainly not mentioned in the Thunderbolt documentation if it is.
> 
> DaveB, NZ
> 
> ----- Original Message -----
> From: "Peter Vince" <pvince at theiet.org>
> To: <time-nuts at febo.com>
> Sent: Thursday, March 27, 2008 2:29 AM
> Subject: [time-nuts] Buffering the 1pps output from a Z3801A
> 
> 
> > Bruce, et al,
> >
> > The 1pps output of an HP Z3801A and Trimble Thunderbolt is
> > only available (as far as I know) as a balanced ECL signal on the
> > 25-pin connector, with dire warnings in the manuals about not
> > earthing either side of the ECL signals.  Would you be able to 
> > advise
> > on a simple buffer circuit that would allow me to drive the usual
> > unbalanced 50-ohm coax please?
> >
> > Thanks,
> >
> > Peter Vince  (London, England)
> >
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