[time-nuts] Where does the Z3801A 1 PPS come from?

Bill Jones, K8CU k8cu at realhamradio.com
Sun Mar 13 12:05:52 EST 2005


On the Z3801A the 1 PPS from the Motorola GPS receiver is sent to pin 82 of
the CPU (U32). From there, the Z3801A 1 PPS output is sourced from the CPU
on pin 78 and eventually drives the output line driver at U6.

The 1 PPS is definitely not simply divided from the 10 MHz oscillator

Bill Jones, K8CU

----- Original Message ----- 
From: "John Ackermann N8UR" <jra at febo.com>
To: <time-nuts at febo.com>
Sent: Sunday, March 13, 2005 4:51 PM
Subject: [time-nuts] Where does the Z3801A 1 PPS come from?

> I asked myself that question the other day and decided to see whether
> the 1pps was simply divided from the 10MHz frequency, or whether it was
> actively stepped.  So, I started an experiment with the time interval
> counter to compare the 1 PPS output* with a 1 PPS signal from an
> external divider on the 10MHz output.
> Here are the results: http://www.febo.com/time-freq/plots/z3801a-pps.html.
> There is about 2.5ns of peak-to-peak variation between the two (with 100
> second averaging, and measured over about 36 hours as I type this).
> That's not much, but there's an interesting very linear daily sawtooth
> pattern.  I have no idea what to make of it, other than it indicates
> some sort of active steering is going on separate from the oscillator
> discipline.
> John
> * Picked off using Jeff Mock's hardware mod at
> http://www.shoshin.co.jp/computer/lantro/html/z3801a.htm
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