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

[Said Jackson]

Hi Hal,

I think its a slow driver, and a complex output impedance, not necessarily a weak driver.

I have a Tbolt hidden somewhere and would need to dig it out. My 30 foot cable disappeared though, so I need to buy a new one :(

On the small hump, i don't think that is a reflection. The signal risetime is just too slow to create such fast spurts. I think it may be a capacitor bridging a larger series resistor. Yuck.

Oh, on the z3801 I thought it had a bnc 1pps output as well..

Bye,
Said

Sent From iPhone

> On Sep 16, 2014, at 13:07, Hal Murray <hmurray at megapathdsl.net> wrote:
> 
> 
> 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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