[time-nuts] Re: Oncore UT+

[alan bain]

On Wed, 16 Nov 2022 at 03:19, Gerhard Hoffmann via time-nuts <
time-nuts at lists.febo.com> wrote:

>
> Am 2022-11-15 12:28, schrieb alan bain via time-nuts:
>
> > A better reference was clearly needed. To convince myself I don't need
> > a
> > Caesium standard I decided I needed a GPSDO.  I've been modifying one
> > of
> > those Lucent RTFG-u REF-0 boxes following Peter Garde's excellent
> > instructions (because it looked fun).  All was going well until i found
> > my
> > Motorola Oncore module believed to be a UT+ when bought was in fact a
> > GT+
> > and didn't provide some of the T-RAIM messages the HP needs (the GT+ is
> > a
> > navigation receiver).
>
> I have bought a Ref-0 and a Ref-1 unit from that guy in Florida, maybe
> PyroJoe?
> Some people around here did that, too.
> The units were still shrink-wrapped, never been on a telecom tower.
> The ref-1 units have the GPS-Receiver, the ref-0 units don't. Not even
> an
> antenna plug. The ref-1 units were quickly sold out, but nobody wanted
> ref-0 w/o GPS. I got a price I could not refuse for the leftover ref-0
> units,
> each had a 5 MHz MTI-260 oven as hot spare (so does have the ref-1).
> I ended up with abt. 20 ovens. :-) Better deal than those Chinese MV89A
> that are removed from their boards with hammer & sickle and best used
> for
> 5 MHz SC crystals.
>
> I have a back burner project of locking a lot of these MTI-260 slooowly
> to the GPS source and Wilkinson-combine the outputs together with the
> intent to get 2*2*2* 3dB phase noise improvement. The board for 4
> oscillators is still in statu nascendi. Ḿaybe XMESS.
>
> The 10 MHz test point of the ref0 has ugly phase noise.
> I made a doubler/distributor for the ref1, directly from the oven.
> Nothing special, mostly LM6702 or ad8000 CFB op amps.
>
> <  http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf  >
>

That's very useful - I noticed the 10MHz test port fed to SA seemed a bit
"messy" in the unlocked state and good to have
an excuse to test a few crystals on the VNA and also the distribution
amplifier is useful (especially one that doesn't do DC
restoration!)


> Please, where is that stuff from Peter Garde?
>
> The (excellent) article I found was this

https://www.eevblog.com/forum/testgear/economical-option-for-precision-frequency-reference/?action=dlattach;attach=172662


And it all worked - it's just that with the wrong oncore, 36s after
initiation of the module it went into a GPS error state which seemed from
my analysis to be
lack of an @@En message from Oncore. It just looped around doing that -
although it determined my position fine and tracked 6 or so
satelites (cheap window antenna).

Alan