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Fw: AO-51 L/u Synopsis

Hello Bob, Ed and BB,

Mike Seguin, N1JEZ  did some actual testing on AO-51 L/S mode.  I am 
forwarding his email to the BB from last August.

----- Original Message ----- 
From: "Mike Seguin" <n1jez@verizon.net>
To: "AMSAT BB" <amsat-bb@AMSAT.Org>
Sent: Monday, August 09, 2004 10:53 AM
Subject: [amsat-bb] AO-51 L/u Synopsis

> The first AO-51 "Experimenter's Wednesday" took place on 08/04/2004. The
> satellite was configured for L/u voice. For those that might have missed
> hearing the first pass, Patrick, KA9SCF recorded it and has an mp3 at:
> http://www.warpcore.com/AO-51-20040804-0227.mp3
> Based on information supplied by 13 of the satellite operators who worked
> L/u, I've extrapolated what I feel is a good starting point for those
> interested in trying the L Band uplink. This is based purely on my own
> experiences working other L Band stations and reviewing data sent by other
> successful users.
> I am not going to recommend equipment, rather EIRP necessary for several
> levels of performance. There are many ways to generate the necessary 
> uplink
> power, so trying to list them all would be a huge task.
> EIRP is a combination of rig power output, coax losses, and antenna gain.
> You'll want to make some basic calculations to arrive at your EIRP. Here 
> are
> a couple of URL's that may help. The first is for loss for various types 
> of
> coax at 1269 MHz.
> http://www.ocarc.ca/coax.htm
> Once you know your rig power out, coax loss and antenna gain plug them in
> here:
> http://www.csgnetwork.com/antennaecalc.html
> First I'd like to thank the following for sending data on their systems:
> Based on data from the above, I'd like to recommend users consider putting
> together the following L Band systems to be used on L/u Voice:
> For an occasional contact, 150 watts EIRP.
> For medium level performance, 500 watts EIRP.
> For superior performance, 1 kW EIRP or higher.
> 1.) L Band doesn't like trees. Depending on your power level, you may need
> to see clear sky.
> 2.) Doppler can run as high as +/- 28 kHz. You must tune your uplink to
> compensate.
> 3.) The satellite L Band receive antenna is linear. This would seem to
> indicate that a circular antenna on the ground would be best. Of the 13
> users surveyed, 5 used linear and 8 had circular antennas.
> For those that may not have seen it, here is a picture of the dual band 
> L/S
> receive antenna designed by Stan Wood, WA4NFY. It is essentially a 1/4 
> wave
> design. For size perspective, it is built on an SMA connector.
> http://members.aol.com/mike73/images/ls.jpg
> 4.) As you reduce uplink power, Doppler correction and antenna pointing
> accuracy become more important. I was able to hold the L uplink with a 
> mere
> 50 watts EIRP, BUT only after I had fine tuned my antenna and carefully
> adjusted Doppler for the center of the receiver capture window. Mark, N8MH
> was using about 170 watts EIRPc and we did make a contact. There was a bit
> of white noise on his signal, but he was quite readable.
> 5.) At the 500 watt EIRP level, #4 is still important but it is much less
> severe. Operation is pretty easy. An interesting observation was made by
> Clare, VE3NPC. He runs 500 watts EIRPc. He was experiencing drop outs as 
> he
> talked. When his FM deviation was reduced, it seemed to clear up the
> problem. This was a very limited test, so more work needs to be done here 
> to
> see if this is a factor or not. I have seen this effect on marginal 
> signals
> into FM repeaters where an operator will be dropping out. He is then told 
> to
> back off his mic and he'll then hold the repeater.
> 6.) At the 1 kW and above level, operation becomes very easy. There still 
> is
> the need for Doppler correction, but the window is easily +/- 5 kHz.
> 7.) An HT with 5 kHz steps could perhaps work, but if the EIRP is small, 
> it
> might tend to be spotty unless Doppler were close to a 5 kHz step.
> Unfortunately, I'm not aware of anyone making contact with an HT this time
> around. The best I could do was test the effects of using lower power. It
> _did_ work! Who will make the first L/u contact with an HT and small beam 
> on
> the uplink?
> Please remember this is all based on just one day of testing with a
> satellite that is still being commissioned.
> Finally, don't be afraid to try whatever you might have. Hopefully some of
> the suggestions above will aid in your success.
> 73,
> Mike, N1JEZ
> AMSAT #29649
> Local Area Coordinator
> "A closed mouth gathers no feet."
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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