[time-nuts] UPDATE: DATUM 9390-52054 Grief again...

[David I. Emery]

On Fri, Apr 12, 2013 at 11:48:47AM -0700, Burt I. Weiner wrote:
> Sorry for the delay in posting this update.  Things have been hectic, 
> and then there was NAB.
> 
> Here's what I've discovered:  The receiver started working after 
> about 6 hours of just sitting.  However, the 9390's internal Vectron 
> oscillator was quite a ways off frequency and did not want to lock 
> after trying to stabilize all night.  I had to tweak the adjustment 
> screw quite a ways and then, after a while, it locked.  Prior to this 
> episode the oscillator had been sitting at only a few E-12.  I 
> suspect that this oscillator has had an intermittent problem for a 
> long time, and I should not have had to tweak it as far as it wanted 
> to go.  The receiver portion has not failed in the few weeks since it 
> decided to start seeing satellites again.  Maybe because I had 
> tweaked the oscillator?

	I have an ancient 9390 that has an ancient Trimble GPS board in
it that takes a 16.368 reference synthesized from the 10 MHz standard in
a PLL loop with a VXCO. This is used in the L band downconversion... 
and for timing generally and given that is PLL derived from the 10 MHz
quite likely if the 10 MHz is significantly wrong the receiver won't
find satellites.   I remember I had to fix this PLL in my box before the
receiver in that box would lock up... initially the PLL wasn't locked,
but the 16.368 VCXO output WAS present  - so for that receiver it has to
be pretty close to right on to work.


-- 
  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."