[time-nuts] 9390 GPS RX

Ed Palmer ed_palmer at sasktel.net
Sat Jun 1 13:36:20 EDT 2013

On 6/1/2013 9:47 AM, Mark C. Stephens wrote:
> Yep, Phase plot is like a Saw tooth.

So, despite the 'lock' LED, it isn't locked.  Well, maybe something's 
locked, but we're not sure what.

> I plugged the house standard as external reference (I am sure I did that already) and it still drifts so there is something wrong there somewhere.
> I also measured the DAC voltage going to the FRK and it's not moving from 0.95 volt.
> Without schematics I am pretty much stuck at this point.
> I doubt if the Schematic for that RX was ever released.

I'd take a shot at reverse engineering the connections to the receiver.  
See if you can talk to it or, at least, see if the 1 PPS coming out of 
it is actually locked to GPS.  Maybe that's what the 'locked' LED means.

> BTW, there are ~120Hz varying on those 1st 2 SMB connectors
> The first is Sine, the second is square.

That's the two that go to the OCXO?  You'd have to trace out the OCXO 
board to see if that made sense.  I would have expected to see a sine 
wave output from the board and an EFC DC voltage input. 16.618 MHz could 
be divided down to 125 Hz which might be used as a reference for phase 
comparison.  120 Hz would work if the crystal was 16.617 960 MHz.  Now 
that I think of it, that OCXO should be checked to see to see how far 
it's drifted over the years.  Whether it's supposed to be phase-locked 
or free-running it could have drifted out of range.

> So, Plan is to Shelve it, on the off chance someone needs bits or I find a parts donor.
> Bit disappointed really, good looking piece of kit.
> I have about 1100 other projects on at the moment and they are all falling behind..

Yeah, I know what you mean.  My problem is, I'm too stubborn to give up 
on a project.  My project list and workbench suffer from the backlog.  
Oh well, it's been fun.  Of couse, you now have a working FRK so the 
project wasn't a total loss.


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