[time-nuts] DATUM 9390 Info wanted

[David I. Emery]

On Tue, Sep 11, 2007 at 09:20:43PM -0600, Don Wisdom wrote:
> Hi,
> I was curious if anyone could tell me a little bit more about the DATUM 9390
> clocks.  Primarly  whether it uses a propatary antenna & whether it is
> indeed gps based or loran or ??  Also if anyone has a manual available
> that'd be cool.

	I have one of the rubidium version  I bought off Ebay several
years ago.   Somewhere (and I mean somewhere in tons of stuff) I have a
partial set of prints and a manual, though I am not sure the prints
exactly match  the boards in my unit - there apparently were several
revisions of the thing.

	My unit uses a very early Trimble GPS board that takes a normal 
1574.2 MHz L band input (no special downconverter in the antenna or
other non standard rf stuff).  I have used it with conventional GPS
antennas but as I remember by default it was wired for 12 volt rather
than 5 volt power for the antenna.   Changing this isn't too hard as it
is quite possible to rewire the power feed for the antenna to 5 volts.  
I do remember the need to draw a certain amount of current from the
antenna circuit in order to avoid a "antenna fault" message.

	Supposedly the Trimble board does carrier phase tracking, but
how well this works on something so antique I do not know.   Frequency
reference for the receiver is derived from a VXCO that is phased locked
to the disciplined Rb so the entire timing path is coherent.

	My original receiver card had the GPS date problem and took some
fiddling to get the epoch right so it would compute the ephermides right
and find satellites, eventually I obtained an upgraded receiver board
with a PIC chip that twiddled the MSBs of the date message and does
display the date correctly.

	At the moment my receiver is down as the 24 volt to +5 and +-12
volt DC to DC converter died and I haven't got around to finding a
replacement that fits in the space provided.   If someone on the list
has a hanger queen with this board available I'd be interested....


-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."