----- Original Message ----- From: w7lrd@comcast.net Subject: [amsat-bb] L'ers equipment
Hello I would like an informal survey regarding what you are using for Mode L. I am working on my system and do not want reinvent the wheel. The format of radio-power-transmission line-antenna/gain.
Hi Bob,
I posted this a while back, but it still should be good:
==== 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.
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: CT1EAT, G3VZV, G3WDG, IZ1ERR, KE4AZN, N5TD, N8MH, NA2P, VE3NPC, VE7BPB, W2XB and WA1ECF.
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.
COMMENTS: 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." ----