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