Re: Q0-100 Web-SDR 198Hz frequency error


Andy G4JNT
 

The same discrepancy of 190Hz is - to within a couple of Hz - there today as well.
Looking at the block diagram of the WebSDR I see they use an Airspy locked to the same GPSDO, but does anyone know for certain how the Airspy interprets the tuning information it is sent?

The FDM-Dup used at my end, when set to USB the 'dial' frequency is that of the suppressed carrier, or a zero frequency tone.
Is this the same setting used on the Airspy?
Could there be an offset introduced somewhere in the setting chain?   The frequency setting of GH appears to be  in 30Hz increments, but rounding to something else.  IN all cases, I used the actual value showing on the display (shown in kHz)

Comparing the two beacon signals to my (all locked) uplink, they are within 1Hz of each other when using both my downlink and Goonhilly.   SO the beacon signals can still be used as reliable frequency offset indicators to Hz accuracy.

BUT, the keying of the upper and lower beacons  takes a bit of interpreting as to which tone is which.

For CW listening purposes both key in the same direction, rest/carrier  and key down are on the lower of the two tone frequencies.    Key up is 400Hz above that.   (The opposite to the standard defined for terrestrial beacon keying, I think)
On the lower beacon at 10489.500 the lowest frequency, is the reference 10489.50000,   and key up is the higher freq, moving into the passband
But
On the higher beacon, the carrier /key down is 400Hz below the edge of the passband and the key up higher tone is the one that defines teh passband edge at 10490.000000MHz


Andy


On Wed, 23 Jun 2021 at 13:31, Andy Talbot <andy.g4jnt@...> wrote:
As mentioned yesterday, I measured this Doppler a while back and you can read it at http://g4jnt.com/QO100_Stab.pdf   but that is not the issue here.

The discrepancy spotted yesterday is between my FULLY LOCKED system  and the GOONHILLY Web SDR.
I see I hadn't actually measured the Goonhilly accuracy back in those tests of 2019, that was all about satellite and the ground station beacon's stability.

Will do some more tests before too long..



On Wed, 23 Jun 2021 at 13:25, Dave_G0WBX via groups.io <g8kbvdave=googlemail.com@groups.io> wrote:

WRT:

From: Gary M1EGI
Date: Tue, 22 Jun 2021 10:33:22 PDT

Hi Andy,

Could some of this be explained by the satellite itself?

Oscillators used, thermal changes onboard due to activity on the main payload?

Just a thought.


Plus the bird itself is not in a true fixed point (WRT the ground stations).

If it's part of a cluster in particular it will move around, I think in a 24 hour cycle.

What does the unexpected offset show 12 hours later, if some 200Hz the other way, maybe that's the cause?

This was explained to me some years ago, by one of the site guys we worked with, when involved with a new DBS uplink install that we were providing the TX PA's for.   But I don't remember the sort of figures he illustrated things with, but the frequencies used were in the 12 GHz area.

(That, as a result of a question I asked, relating to why the antenna positioners kept whirring every few minutes, if the satellite was in a "geostationary" orbit.   That resulted in a good 45 minutes very interesting diversion from amplifier problems, and a visit to one other much older uplink facility on the same site, to see a chart recorder output.)

73.

Dave G8KBV

 



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