[time-nuts] HP Z3801A - How to convert the 1PPS & 10MHz Differential Pseudo ECL Output?

Hal Murray hmurray at suespammers.org
Sun Apr 9 21:36:20 EDT 2006

> I didn't convert the PECL signals, but instead went inside the unit
> andtapped off the 1pps and 10MHz signals.  I have details at
> http://www.febo.com/time-freq/gps/z3801a/mods/index.html 

You don't need to install the jumpers.  If you look around, there are unused 
0R slots near the ones you remove.  You can install 0R resistors there to get 
RS-232 levels.  It's pretty obvious if you poke around with an ohmmeter.  You 
can recycle the ones you remove so your shopping list gets shorter.

I don't have a quick/easy answer for how to convert the 10 MHz.  If I wanted 
to connect it to digital logic, I'd probably AC couple it and bias the 
receiver at the threshold.  If it was a CMOS receiver, I'd probably try 10K 
pullup and 10K pulldown.  For a TTL chip (HCT as well as real TTL), adjust to 
get 1.4V.

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