[time-nuts] GPS timing recievers and INTERFERENCE

[James Maynard]

Glenn wrote:

> 
> BTW, Timing accuracy of the UT+ is listed as "In position hold mode, 
> <50ns (1 sigma) with SA on." Does anyone have claimed or measured values 
> for timing accuracry WITHOUT SA?
> 
I'm using an M12+ timing receiver, included in my new "CNS Clock II) 
from Rick Hambly of CNS Systems. In the manual for the CNS Clock II, 
Rick claims 20 ns or less one-sigma jitter on the 1 Hz pulses. On his 
Web page describing this product,

     http://www.cnssys.com/cnsclock/CNSClockII.html,

Rick claims typical jitter of plus or minus 27 ns (15 ns one-sigma) 
without the "High Performance PPS Option."  With that option, which 
provides a hardware correction for sawtooth error on the 1 PPS output, 
he claims plus or minus 11 ns jitter on the 1 Hz output pulses (3 ns 
one-sigma).

I am seeing a one-sigma jitter of about 9 or 10 nanoseconds.  This isn't 
as good as Rick claims, but then my antenna location, although up on the 
roof, is shadowed by some rather large trees and may be experiencing 
some multipath effects.

As to its absolute accuracy, I don't know, because I have not completely 
allowed for cable delay from the antenna to the M12+, nor for cable 
delay from the M12+ to my time interval counter. Also, I'm still waiting 
for final settling of the long-time-constant phase-locked loop by which 
my Rb frequency standard disciplines its frequency to agree with the 1 
Hz pulses from the GPS receiver.

If the M12+ timing receiver had an optimum antenna location, with 
multipath suppressed, I think the 3-nanosecond one-sigma accuracy on the 
timing pulses is probably acheivable. That is, I have no reason to doubt 
Rick's measurements. With my installation, however, I see more like 
10-nanosecond one-sigma uncertainty.

-- 
James Maynard, K7KK
Salem, Oregon, USA