[time-nuts] Short Terms Stablity of the Trimble Mini-T
Rex Moncur
rmoncur at bigpond.net.au
Wed Nov 7 21:28:35 UTC 2007
I am new to this list - so apologies if I am going over old ground. Is there
an archive that I can look back on?
I have been comparing a recently purchased Trimble Mini-T with a HP Z3801A
and getting short term frequency variations of 1 Hz and more at 1296 MHz
with a period that varies from a few 10 of seconds to a minute or more.
This equates to a short term stability of around 1 part in 10^9 compared to
the 1 part in 10^10 I was expecting from the Allan Deviation specs. There
has been no improvement after running the Min-T for more than a week.
I admit to not fully understanding the relationship between Allan Deviation
and short term frequency stability. So I would be grateful for advice as to
whether there is a simple relationship?
Now I don't know if the stability issue is the Mini-T or the HP Z3801A but
the clue is that if I remove the antenna from the Mini-T the short-term
stability improves by a factor of 10, so I am reasonably confident that the
problem is with the Mini-T. Does anyone have experience with the Mini-T and
what sort of short-term stability one should expect?
Now a clue as to whether there is a problem is that it appears that when GPS
locked the Mini-T is overshooting like it has too much control loop gain. A
further clue is that after a period with the antenna removed the frequency
overshoots one way or the other up to several Hz before coming back to the
correct frequency. I have not yet connected the Mini-T to a computer so it
is possible there is some adjustment I can make.
(I can send a frequency plot on Spectrum Lab to anyone who might find this
useful)
73 Rex VK7MO
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