R: [amsat-bb] Help with L1 uplink on AO-40

["Joe Steinmetz" <joes@xxxxxxxxxxxxxxx>]

Just wanted to update the list on this thread.

Thanks to all the replies I received. There were many very useful emails I
received. Lots of good help out there.

I understand things much better now. My findings are below:

-I neglected to adjust the reflected power by the cable loss, thinking it
was only 2 watts, when in fact it was really more than 4. The SWR was
greater than 2.

-the 2:1 splitter on my phasing harness was the culprit, removing it dropped
the reflected power to less than 1 watt including the cable loss. The SWR is
now less than 2.

Other observations and things suggested by others via email:

-L band with squint angles above 10 degrees requires > 1000 watts EiRP.

-a 12 turn helical doesn't really have 14dBic gain and therefore combining
two doesn't really give me 17dBic. More like 14 dBic combined...you mileage
may vary.

-put the amplifier at the antenna and run an up converter with 2m IF to get
around the cable loss.

-use a dish rather than helicals, better gain an no need to fuss with
phasing.

So, after removing my broken splitter and using just one 12-turn helical
with about 30 watts at the antenna with the squint angle less than 10
degrees I was able to hear my own signal on the downlink sufficiently above
the noise floor to make a QSO (although I didn't actually make one). So it
does work after all.

It was pointed out to me, and now it makes sense, that to make L band
useable with squint angles greater than 10 degrees (which is a goal) one
needs greater than 1000 watts of EiRP. So that means I need to move my
amplifier to the antenna as well as improve the gain of my antenna. That is
my next project.

I am thinking of using a 1.2m dish (dumping the helicals) to accomplish more
gain. This is an offset dish and a bigger version of the one I use for S
band RX/TX. Any suggestions on feeds for this dish are appreciated, I was
thinking either a helical or patch but am open to other ideas or comments by
others.

thanks for the help,

Joe
k6sat

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