[amsat-bb] Re: L'ers equipment

Mike Seguin n1jez at verizon.net
Wed Sep 13 17:58:35 PDT 2006

----- Original Message ----- 
From: <w7lrd at 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:


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


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

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.


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.

Mike, N1JEZ
AMSAT #29649
Local Area Coordinator
"A closed mouth gathers no feet."

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