[time-nuts] DATUM 9390 Question...
w2hx at w2hx.com
Wed May 18 03:02:32 UTC 2011
Hi Burt, thanks for the excellent information and your experiences with this
model! I have to models, the -52054 and -52117
The 52054 seems to see the SVs much more easily. The 52117 using the same
antenna and antenna location sees nothing (I haven't tried moving the
antenna to a substantially better location yet to see whats what). I wonder
if they have different receivers in them? I have yet to open them up.
Thanks for relating to me that this disappearing SVs is not uncommon. It is
counterintuitive, but who knows what they were thinking when it was
designed. I did the master reset procedure quite successfully as the LAT
and LON both reset to the numbers in the manual.
My two dacs (on the two models) are at about 28,000 and 39,000 hopefully
that is sufficient to stay in range of the DAC.
Bottom line, thanks a lot for the info. Very helpful to know I am not alone!
73 Eugene W2HX
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Burt I. Weiner
Sent: Monday, May 16, 2011 9:43 PM
To: time-nuts at febo.com
Subject: [time-nuts] DATUM 9390 Question...
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.
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