[time-nuts] GPSDO module connections

Charles Steinmetz csteinmetz at yandex.com
Mon Mar 3 14:49:23 EST 2014

>Is it OK if I'll take some RG-59 from CCTV, cut 6" or 12" of it, 
>connect one end to GPSDO (let say this cable has compression type 
>connector) and solder other end to BNC on the panel ? Or its better 
>to use adapters and no soldering ? Like "F connector-to-BNC" adapter 
>, then short BNC-to-BNC cable connected to BNC panel connector ?

The fewer adapters the better, and it is best to avoid solder-type 
panel connectors entirely (if what you mean is a non-coaxial 
connection with the center conductor soldered to the center pin and 
the shield separated and attached to the panel or the connector 
body).  Best to keep it coaxial all the way.  So, the best solution 
would be a piece of RG-59 with a male F connector on one end and a 
female, rear-mounting, panel mount BNC on the other end.  If you do 
not have the facilities to make up your own coaxial cables with crimp 
or compression terminations, there are a number of ebay vendors who 
will do it for very reasonable cost (or you may well find the 
"pigtail" cable you need already made).  Alternatively, you could use 
a cable with a male F connector at one end and a male BNC at the 
other end, connecting to a female-to-female bulkhead connector at the 
panel.  But that is one more connection, which is better avoided.

One further consideration is whether the shield of the panel-mount 
connector should be galvanically connected to the panel, or insulated 
from it.  If you have problems with ground loops, insulating it may 
help.  If you do insulate it, the shield should be bypassed to the 
panel right at the connector with (for example) a 0.01uF capacitor 
paralleled by, say, a 1k ohm resistor.

>is it worth to use RF cable to connect 1PPS output from GPSDO to 
>distribution amplifier ? Or regular AWG-22 could do that job ?

The PPS signal has a tendency to leak everywhere because it is a 
short pulse with fast edges.  If you bring it out of the box you 
definitely need to use coax.  Good, quad-shielded coax.  Really, you 
should use triaxial cable, but that is enough hassle that few people 
do it.  If you don't have a pressing use for the PPS signal, it is 
best to leave it inside the box.  You can mitigate the leakage by 
slowing down the edges, but that may compromise the utility of the 
pps by increasing jitter in the trigger circuitry of whatever you 
feed with it.  If you bring the PPS out of the box, you will need to 
make sure it is properly terminated to preserve the pulse shape.

Best regards,


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