[Gb-ccb] 1PPS signal specifications

[John Ford]

Hi Martin.  It's amazing how quickly things that never give you trouble
migrate to the bottom of the drawer and are forgotten...

The drivers for the 1 PPS are set up to drive a 50 ohm coax to a
voltage level of 4.0 volts. The pulse is a 1 microsecond wide
positive-going pulse, rise time 6.5 ns typical, fall time, 5.5
ns typical  Short circuit protected, 150 ma output maximum.

I think a good setup would be a grounded BNC connector, a ferrite bead
on the center conductor inside your enclosure, and a good
double-shielded cable between your box and the 1 PPS signal source.
The cable will be about 22 meters long.

John

Martin Shepherd writes:
 > I need some more information about the GBT 1PPS signal. From previous
 > email, I know that this will arrive at the CCB via RG58 coax
 > terminated in a male BNC connector. What I now need to know are the
 > mark-space ratio and amplitude of the 1PPS pulses, and whether the
 > coax is going to be sufficiently long that I need to guard against
 > ground loops through the cable shield (eg. I could either use Amphenol
 > ground-filtered BNC sockets, along with extra RFI filtering of both
 > the shield and signal connections, or I could use normal uninsulated
 > BNC sockets, and just RFI filter the signal connection).
 > 
 > Martin Shepherd  (mcs at astro.caltech.edu)
 > 
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