Is it normal for reflected power to be so high?

For the early roll-out of the Dashboard

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Is it normal for reflected power to be so high?

Postby WB4SON » Fri Nov 22, 2013 4:20 am

I was wondering if this is an issue of scaling, or if there was some sort of implied issue with the transmitter/antenna?

Forward power has been running about 400 mW, and Reverse Power has been running about 240 mW over the two passes I monitored tonight. If the scale is correct, that seems to be a pretty bad SWR, something like 9.6:1, right?

73, Bob, WB4SON
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Re: Is it normal for reflected power to be so high?

Postby g4dpz » Fri Nov 22, 2013 6:36 am

Hi Bob.

We noticed that problem early into the flight yesterday and we spent a good deal of the day using the data we had received through the warehouse to model the swr change over several orbits.

We believe it is a calibration error in the slope of both the fwd and rev sensors.

We think that our choice to provide the dashboard and warehouse was a very wise decision and we thank the 40 plus people who uploaded data for their support.

It's going to be another busy day of checkout and PR.

73

Dave, g4dpz
AO-73 satellite team
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Re: Is it normal for reflected power to be so high?

Postby g0mjw » Fri Nov 22, 2013 11:05 am

Something very strange happened towards the end of the last pass. The transmitter power telemetry showed a large drop from 350mW down to 40mW , so did the bias current, 110mA to 35mA and PA temperature,14C down to 8C. I also lost a few packets and the satellite went into Eclipse (surely it didn't).

I am hoping this was due to commands trying to bottom out the high reflected power issue and/or testing the transponder.

Mike
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Re: Is it normal for reflected power to be so high?

Postby g4dpz » Fri Nov 22, 2013 11:55 am

Hi,

We commanded the satellite into transponder mode on that pass so the beacon drops to 30 mW.

On the FUNcube dongle you can see the beacon and the passband noise floor.

We may do the same on the next pass but it's only 22 deg. elevation to us so we may hold off until later
today.

We will be working on characterising the SWR problem today and changing the Dashboard and Warehouse
scaling and offset calculations.

Also you may have noticed that the battery value may have very high values, this is a problem with roll
over of the data. Values 253 = -2 254 = -1 255 = 0 we are working on these

73

Dave, G4DPZ
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Re: Is it normal for reflected power to be so high?

Postby g0mjw » Fri Nov 22, 2013 12:35 pm

Hi Dave,

I figured that out once you posted you had had a QSO. I heard you calling on the last 22 degree pass and I called you back, but no response. Probably I wasn't netted properly. I need to program the TS2000 to tune automagically but I have to be careful not to transmit on 2m by mistake as the FCD is plugged in. Another satellite passed over directly afterwards and I could hear someone calling in Russian. I don't know if it was another satellite from the latest launch or once of the older satellites in the same orbit. I can imagine QRM issues if these drift together.

Mike
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Re: Is it normal for reflected power to be so high?

Postby g8sqh » Fri Nov 22, 2013 7:49 pm

I noticed this last night, but it seems only to occur when she's in eclipse - data from VK had normal SWR, as did data from the UK this morning. I suspect the temperature change affects the fwd/rev power detectors - to be expected if they use normal diodes. Can't see any obvious way the antenna would detune that much when cold

On the good side, the battery voltage is steadily creeping up. Once it reaches 8.4V, will the solar panel energy be dumped into shunt resistors? That would get the battery above 0C rather nicely
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