[time-nuts] Correcting jitter on the 1 PPSsignalfromaGPSreceiver.

Hal Murray hmurray at megapathdsl.net
Tue Sep 16 16:07:50 EDT 2014

SAIDJACK at aol.com said:
> here are some plots from two GPSDOs, one series terminated (CSAC GPSDO),
> and one load-terminated (Agilent 58503A) product. 

Nice pictures.  Thanks.

My reading of your pictures is that the 58503A has a weak driver.  Do you 
have a TBolt?

> ... and there is a little hump right at the beginning.

That could be a reflection from an impedance change.  I wonder what's inside 
the box.

> I don't know what the output circuit of the 58503A looks like, but
> assuming that it probably is the same as on the Z3801 units many folks  here
> have it is quite relevant to this discussion, and comparing these two
> approaches  really shows the quality difference between these two products'
> signals.

The Z3801 doesn't have a simple BNC connector for the PPS.  Their are 2 pairs 
of differential PECL signals on the DB-25.  I haven't looked at them.

If all you want to do with the PPS is feed it to NTP, you don't need ns level 
accuracy.  There is a standard recipe for converting the RS-422 levels to 
RS-232 and borrowing one of the drivers for the PPS signal.   RS-232 drivers 
are deliberately slow enough to avoid most of these problems.

The 10 MHz comes out on a BNC.  That's what most hams use for multiplying up 
to GHz.

These are my opinions.  I hate spam.

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