[time-nuts] Picked up the Austral 2200A tonight

paul swed paulswedb at gmail.com
Thu Jul 30 11:30:13 EDT 2015


Jason
If you build a single conversion front end as you suggest, then the LO will
be 1500 MHz and low side injection causing a 180 degree phase flip.
Hopefully not a real issue.
The thing I ran into when I built my solution is that front end LO had to
be locked to the 10 Mhz out of the Austron. The Austron directed the LO to
establish a stable phase relationship through the receive chain. So the DDS
master clock should in some way be controlled by the Austron 10 MHz. A
thought would be 6 X 10 MHz filter it and drive the DDS.
Now the funny thing about a DDS is that they don't often run atthe exact
frequency you need. Always a bit high or low unless the math is worked out
ahead of time.
That drift will make the austron reference drift as it tries to correct it.
(Null it out)

With a single conversion process the IF filter will be a bit complex. It
has to be several MHz wide and 75.42 is the center frequency. Then you may
need some IF gain perhaps 10 DB as a pure guess.

There is no pps or 10 MHz out of the unit till locked.
However if you go to the output board the 10 MHz is there and goes to a
gate that you can force to always provide the 10 MHz. I do not recall if I
marked that down or not.
Regards
Paul
WB8TSL

On Mon, Jul 27, 2015 at 5:56 AM, Jason Ball <jason at ball.net> wrote:

> Just picked it up, it has an internal rubidium which piqued my interest as
> worst case I could cannibalize the unit.  It's also been sitting on a shelf
> for > 10 years so the oscillator should hopefully have some life left in
> it.
>
> What does surprise me is the firmware is dated 25th August 1998, I was of
> the opinion these units weren't Y2K compliant and would have assumed an
> update in 1998 would have been tested...   gps rollover not withstanding.
>
> Is there anyway to get the 10MHz output running off the rubidium without a
> satellite lock ?   I can't seem to trigger it just yet.
>
> My plan is to use a DDS to generate a 1.Ghz LO and to feed this into a
> suitable mixer to down convert to the 75.42Mhz input signal for the gps
> reference as a start to see if I can get the thing working, allowing for
> the 1024 week offset of course.  Just waiting on parts at the moment.
>
> Cheers
> J.
>
>
> --
> --
> Teach your kids Science, or somebody else will :/
>
> jason at ball.net
> vk2vjb at google.com <vk2flnx at google.com>
> callsign: vk2vjb
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