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Re: Gettng on AO-40 - Uplink Antenna


I use a Gulf Alpha Antenna for 70cm, and have been very happy with it. I also
use a FT-847 and find the 50 watts adequate for AO-40. Circular polarization is
more important on AO-40 currently, due to spin fade - if and when we go to
3-axis stabilization on AO-40 you won't need circular polarization, and linear
polarization will be a benefit - be aware that there has been no schedule
announced for 3-axis stabilization, and it may never happen.

If you do go with a circular polarized antenna, you might want to consider a
polarity switcher if you want to work some of the other satellites. While it is
not essential to have polarity switching, several satellites switch between
RHC/LHC polarization as they pass - SO-41 is a good example. When the satellites
switch from RHC to LHC the difference is 20db down - whereas from linear to
RHC/LHC it is only 3db down. Pete at Gulf Alpha is building a batch of polarity
switchers now to offer with his satellite antennas (they are not on his website
yet) - I think they are $129 in addition to the antenna cost. You can always add
it later.


Don Woodward
AMSAT 33535

----- Original Message -----
From: "Mike King - KM0T" <scsueepe@mtcnet.net>
To: <amsat-bb@AMSAT.Org>
Sent: Tuesday, August 13, 2002 00:44
Subject: [amsat-bb] Gettng on AO-40 - Uplink Antenna

Hi all, got some equipment for getting on AO-40.  Looking at a 435 Mhz
uplink antenna.  Hope to be on in a month or two.

Question, is the circular polarization uplink antenna such as a M2 436CP30
verses a single polarization unit a good way to go?  My research has
indicated that there is a 3 db difference to the sat, plus possibly less
fading?  I guess how much better is it in terms of operation?

Also, I understand that the RHC polarization, just set the antenna up for
that, no need to change polarization?  I assume that the A040 antennas
basically allwaya point back at earth in the same polarization.  I guess
what Im asking is if there is any reason or need for a polarization switch
to optimize the uplink signal.

In addition, any comments on this antenna verses the unit from Gulf Alpha
antennas.  That unit is about 3/4 the boom lenght of the 117" M2 unit.  Any
users out there with comparisons?

I will be using a FT-847 with 50 watts out (or less) to one of these
antennas.  Question is that without offending LELIA (I think thats the name
anyway) will 50 watts do the job (assuming reasonable feedline loss of 1 to
1.5 db) or will a brick still be required?  I really dont have a feel for
this as all the reading I have done kind of shows guys using different power
levels across the board.  Also I imagine this has some to do with single
verses circular polarization as well.

So, sorry if this has all been covered before (I would imagine it has) and I
appreciate any info from the veterens on the bird.  Any tips appreciated,
dont want to be a lid.

73 and thank you.

Mike - KM0T en13vc - NW Iowa

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