[time-nuts] On choosing reasonable synthesizer PN requirements

[Brian Lloyd]

On Fri, Apr 24, 2020 at 8:08 AM jimlux <jimlux at earthlink.net> wrote:

> On 4/24/20 5:52 AM, David J Taylor via time-nuts wrote:
> > Hi
> >
> > The “wiggles” he is chasing are about 2-3 Hz (by eyeball on his charts).
> > At 2.4 GHz,
> > that is a fairly convenient ~1 ppb. The Z-3801 (if it was in good
> > health) should be easily
> > able to hold that level of performance. It’s not clear which MD-011 he
> > is using, but it is
> > a pretty good bet it will also hold that level as well. The usual
> > disclaimers about good
> > satellite view for the GPSDO’s would of course apply.
> >
> > Substituting a typical telecom Rb for either device would likely also
> > allow the wiggles
> > to be observed (or not). That would take out the whole dependence on GPS.
> >
> > (Yes I realize those comments are probably better directed to those
> > involved ….).
> >
> > Bob
>
>
> It's a fascinating writeup - the author does time-nut like stuff at
> work, so he looked at the possibilities - is the GPSDO at Bochum
> screwing up (can't actually get in because of COVID-19) - so he compares
> with a locally generated uplink.
> He also compares with the signal from an uplink from Mauritius, so the
> Doppler is slightly different.
>
> I'm going to guess just what he said at the end - some sort of thermal
> thing on the spacecraft.
>

And I would guess the battery charging system. I would love to see the bus
voltage plot superimposed on the The "wiggles". (Is the housekeeping
telemetry decodable?) Notice that the frequency "pop" in the beacon
coincides with the end of the "wiggles". I haven't looked but does the bird
have a planar PV array? If so, I am guessing that this is when the charging
system shuts down as the PV array stops producing output and then shortly
thereafter something else turns off or turns on, the two events creating
the leading and trailing edges of the "pop". If it has a max PPT charging
system (of course it does) I can imagine, as the output of the array falls
off, the MPPT algorithm "hunting" to find an optimum operating point and
causing bus voltage to vary.

Of course, it could always be the Radar Men from the Moon.
-- 



Brian Lloyd
706 Flightline
Spring Branch, TX 78070
brian at lloyd.aero
+1.210.802-8FLY (1.210.802-8359)