Distortion on first part of pass on orbit 31

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Distortion on first part of pass on orbit 31

Postby M0SAT » Sat Nov 23, 2013 2:45 pm

The beacon was distorted (wobbly) for the first 12 degrees of the pass for me on orbit 31 (think that's correct, last day orbit to the West today).

I have checked my horizon and isn't anything that should be causing this problem, in fact on West pass yesterday managed more data than on any other.

Not a phase change and this just fades to static or very noisy, but not distorted.

Looking back FunCube was coming out of eclipse. Is this just coincidence, some local interference to me or did anyone else suffer this?

The distortion appeared to be rectified within one block of data (i.e. one tone was distorted, the next 5 seconds later after data was clean).

It then remained "clean" for the rest of the pass.

Up until it became "clean" although I was able to hear the data and tones audibly nothing was decoded.

Will check on the next passes this evening but Eu will be in Eclipse so the beacon will be switched lower so won't be able to replicate for 24 hours.

Dave
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Re: Distortion on first part of pass on orbit 31

Postby g0mjw » Sat Nov 23, 2013 3:32 pm

Same here Dave - on the following pass the distortion, which seemed like FM, was present all the time and despite a strong signal, I recovered no data. However a few minutes later when it reached North America, it must have recovered as data was flowing again. This seems to happen just out of eclipse so my theory is it is temperature or power bus related. It might be connected to VSWR issue.

Mike G0MJW
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Re: Distortion on first part of pass on orbit 31

Postby WB4SON » Sat Nov 23, 2013 4:42 pm

Wasn't there a notification the satellite would be switched to Transponder Mode for testing during this orbit?

I believe the control folks discovered this same issue, when the Transponder was turned on and the beacon was in low power mode (30mw), so they put they turned the transponder back off and put the beacon back into high power mode.

I wonder if you guys didn't catch the low-power to high-power event?

The control ops are asking anyone with recorded audio to forward it to them for analysis.

73, Bob, WB4SON
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Re: Distortion on first part of pass on orbit 31

Postby M0SAT » Sat Nov 23, 2013 5:57 pm

Glad you heard it as well Mike.

The FM you mention is a good analogy. I did manually tune up & down either side of the beacon for quite some way and couldn't find any specific culprit.

Thanks for your comments also Bob. I don't believe it's a transponder switching issue (i.e. low-high power) as there was no discernible change in signal strength on the radio (I know this is not the most accurate of measures, but it stayed the same and it's all I had in line to measure at the time).

Next time I'll have my camera ready to record it.

I'm not using SDR otherwise I would have recorded the whole spectrum for analysis.

Looking forward to hearing/working the transponder on this evenings passes.

Dave
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Re: Distortion on first part of pass on orbit 31

Postby g3vzv » Sat Nov 23, 2013 9:02 pm

We believe this "problem" was caused by everyone receiving the signal from a spacecraft that was over (or behind) the auroral curtain around the North Pole...think "59A" and consider what a BPSK signal would sound like with auroral spreading.

cheers

Graham
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