Eugene,
I have two of the DATUM 9390-5054 instruments with the original
antennas and 100 foot feedline that I have above tree line and well
in the clear. I have worked with many of this model receiver and my
experience is that it is not uncommon for them to begin to gather
satellites, having all four SVs looking happy and ten drop back down
to none, or only one or two satellites. He may do this once or even
twice then settle down and do his thing. Be patient. There is a
Master Reset performed by turning the unit off, lowering one of the
DIP switches, turning the unit on waiting about 30 seconds and then
turning the unit off and then returning the DIP switch back up. The
bad part is that I don't remember which DIP switch! I'll see if I
can find that in my notes. Really, the only time this is handy, not
mandatory, is when the unit has been moved to a different location
since it was last fully operational. This reset will clear out the
old Almanac and give it a fresh start. Even if you don't do this it
will work just fine but will take a longer time to figure out where
he is and start to gather satellites.
One thing you will want to check is that the DAC number is around
27,000. This can be set by removing the protective cover screw for
the oscillator in the back of the receiver and using a long insulated
screw-driver to set the set the oscillator (Well, I suppose it
depends on which oscillator you unit has in it.). Looking at it from
the back, turning the screw counter-clockwise lowers the DAC and CW
(obviously) raises the DAC. What I have found as a happy way to set
a receiver that has been sitting for a long time is to turn the
instrument on without the antenna connected, let it warm up for a
while and ten setting the oscillator as described above for an output
frequency of 10 MHz - as close as you can get it with out going
crazy. Anywhere within 1 Hz is plenty close enough to make it happy
for a start. Mine usually settle down to 1 to 10 E-12 after about 24
hours. Periodically check the DAC - maybe once a month. It will be
happy if it's between 20,000 to 45,000. Once in a while I tweak mine
back to around 27,000 using the procedure I described above. I never
tweak both, just one at a time, let it settle in for a day or two and
then I'll tweak the other one. A sign that the DAC may be getting
close to its limit is that the instrument will likely drop out of
lock every once in a while or more often depending on how close to
the limit he really is.
I hope this is of some help.
Burt, K6OQK
At 08:02 PM 5/15/2011, [email protected] wrote
> On Sun, May 15, 2011 at 6:30 PM, W2HX <[email protected]> wrote:
>
> Hi there. Recently acquired my first GPSDO. It is a datum 9390 (thank you,
> Norm!). One aspect of its behavior seems strange to me. Within a matter
> of
> a few minutes, it seems that satellites are appearing and disappearing.
> Are
> the satellites moving that quickly? I might go from 1SV to 3SV or 4SV and
> then a minute later go to 1SV or none. The antenna isn't moving and the
> trees aren't moving too much today. I have not done anything with regard
> to
> setting minimum elevation or any other parameters. I did go through the
> COLD RESTART procedure to clear out everything and let it start from
> scratch.
>
>
>
> Do other GPSDO users experience something like this?
>
> 73 Eugene W2HX
Burt I. Weiner Associates
Broadcast Technical Services
Glendale, California U.S.A.
[email protected]
www.biwa.cc
K6OQK
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