[time-nuts] On choosing reasonable synthesizer PN requirements

[jimlux]

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.



> ========================================
> 
> If you follow his Twitter feed:
> 
>   https://twitter.com/ea4gpz
> 
> I think it's all but certain that it's the local oscillator in the 
> satellite-borne transponder is the cause of the problem.  He's looked at 
> an engineering beacon on the satellite too.  The orbital calculations 
> involved need to be quite accurate.
> 
> I thought it might interest those chasing the ultimate precision!
> 
> Probably ought to change the title of this topic, but I'm unsure of the 
> protocol here about so doing.
> 
> Cheers,
> David