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Author Topic: USB/LSB Uplink/Downlink  (Read 8103 times)
K0JEG
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Posts: 669




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« on: November 18, 2012, 06:02:52 AM »

I'm starting to work the linear transponder satellites. Last night I was able to hear myself on the downlink, but not able to make any contacts despite it being a great pass, directly overhead. I'm using an FT897d and FT817 both controlled by Gpredict, adjusting for Doppler shift automatically (tuning the receiver retunes the transmitter to match transponder inversion and Doppler). I did hear a few stations during the pass (VO-52).

I've read a few articles online that explain the linear transponder concept, but none tell you what the accepted practice is concerning uplinking using USB or LSB. Similar to the practice of using USB on 20 meters and above and LSB below. Is it a standard across the board or different for different transponder modes?
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WD9EWK
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« Reply #1 on: November 18, 2012, 08:37:53 AM »

I'm starting to work the linear transponder satellites. Last night I was able to hear myself on the downlink, but not able to make any contacts despite it being a great pass, directly overhead. I'm using an FT897d and FT817 both controlled by Gpredict, adjusting for Doppler shift automatically (tuning the receiver retunes the transmitter to match transponder inversion and Doppler). I did hear a few stations during the pass (VO-52).

I've read a few articles online that explain the linear transponder concept, but none tell you what the accepted practice is concerning uplinking using USB or LSB. Similar to the practice of using USB on 20 meters and above and LSB below. Is it a standard across the board or different for different transponder modes?

The standard for SSB voice communications on the satellites is to end up receiving in USB on the downlink.  VO-52, FO-29, and AO-7 in mode B (70cm up/2m down) all use inverting transponders.  You transmit in LSB to those satellites, and receive the downlinks in USB.  AO-7 in mode A (2m up/10m down) is the only "exception" to this "rule" among our current crop of satellites with linear transponders, where it does not use an inverting transponder.  You transmit to AO-7 on 2m in USB, and receive the 10m downlink in USB. 

If you are able to copy the downlinks, you are off to a good start.  Make sure you are able to do that, before transmitting up to the satellite.  VO-52 is usually the easiest one of those transponders to copy. 

Good luck, and 73!
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Patrick WD9EWK/VA7EWK
http://www.wd9ewk.net/
K0JEG
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Posts: 669




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« Reply #2 on: November 19, 2012, 05:44:52 AM »

Thanks for the response. I tried a pass last night at 19:30 local time but didn't hear anything. Must have been a good football game on after the contest. Smiley

One thing I noticed right away is the increase in coax loss on 70cm compared to using the stock Arrow duplexer and an HT. Of course, the last sat I worked was AO-51, and it always seemed to boom in when overhead. Right now I'm using RG-8x because I have a lot of it on hand. LMR400 flex looks like the stuff to get, but it may need to wait until spring unless I can find some surplus somewhere.
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WD9EWK
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« Reply #3 on: November 19, 2012, 07:59:46 AM »

Thanks for the response. I tried a pass last night at 19:30 local time but didn't hear anything. Must have been a good football game on after the contest. Smiley

Or at the end of the contest - I think Sweepstakes ran until 0300 UTC, for those who wanted to be on at the very end.

Quote from: K0JEG
One thing I noticed right away is the increase in coax loss on 70cm compared to using the stock Arrow duplexer and an HT. Of course, the last sat I worked was AO-51, and it always seemed to boom in when overhead. Right now I'm using RG-8x because I have a lot of it on hand. LMR400 flex looks like the stuff to get, but it may need to wait until spring unless I can find some surplus somewhere.

Unless your coax runs are very short - think around 10 feet or so - or you are running preamps on your receive antennas, you will want to do better than RG-8X on the coax.  Coax losses are very noticeable as you go higher in frequency.  LMR400 is probably a good starting point for improving your coax situation. 

There were times that AO-51 would sound very strong, when the command stations set its downlink to 1W or 1.5W.  That did not happen often, due to the power budget that had to be maintained on that satellite.  But that would be 1W or 1.5W on a single frequency.  VO-52 has a strong downlink, but its transmitter power is shared across all signals passing through the transponder - across a 60 kHz spread.  Unless there is only one signal going through the transponder, or possibly when one station is overpowering the transponder, you probably won't hear too many signals that rival the "high power" setting from AO-51. 

73!
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Patrick WD9EWK/VA7EWK
http://www.wd9ewk.net/
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