[ntp:questions] Odd results with Oncore UT+ ref clock

Chris Albertson albertson.chris at gmail.com
Wed Feb 2 19:06:21 UTC 2011


So many good ideas.  I'll try and answer them all.

(1) cable length.  At this point I don't care about delay of 75 ns.
But there might be attenuation of the signal.  I've not measured it
yet but I doubt it because (a) the serial messages are working fine
and are on the same cable and (b) I'm using a MAX232 chip to do level
conversion TLL->RS232

(2) The clockstats shows that I have enough satellites in view.
Always at least 5.  The UT+ is an 8 channel receiver.

(3) I have the UT+ set to only send PPS when the timing error is
within limits which I think is either 100 or 300 ns.  but clockstats
log shows errors in 40 to 60 range all the time some times going down
to 31 nanoseconds.

There are still things to rule out.  For example I don't 100% trust
the 7404 inverter chip the PPS signal goes through  It could be that
it's CMOS and I don't have level conversion to TTL done correctly.
The PPS blinks a LED just fine but it may not be driving the MAX232
chip reliabely.  The serial data goes direct from UT+ to max232.    I
have a 74F04 on order


-- 
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Chris Albertson
Redondo Beach, California



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