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RE: circular polarized Arrow antenna



Tim Cunningham makes some good points about linear versus circular polarization for portable operation.  But the Arrow antenna definitely wouldn't be handheld when running 50W uplink to AO40.  And the antennas are not likely to be within reach of my operating position in a typical multi-day "holiday" portable operation (antennas outdoors, me and the radios indoors).  But the antenna mount could be designed so that it's easy to run out to the tripod and change the (linear) polarization.  I could transmit a low-power carrier and rotate the antenna for best uplink while listening on headphones.  I already plan to use a long headphone extension cord to facilitate adjusting azimuth and elevation by ear for best reception.  I could tweak TX polarization at the same time.

I'm not likely to attempt a portable AO40 operation unless there are long periods with low squint (definitely less than 20 degrees).  Most of the horizon would probably have obstructions, so I wouldn't operate much below 10 degrees elevation.  Even a 2 dB improvement might be significant for "BBQ dish" people to hear me better.  I would like to verify it myself, but I've heard that CP uplink antennas have less fading in typical AO40 conditions (I have only used RHCP for my AO40 uplink).

With the design of the 7x7 Arrow antenna, the extra complexity of the antenna itself has negligible impact on portability.  Another half pound of aluminum and maybe 2 additional minutes of assembly time to attach the arrow shafts and connect the second feedpoint.

I will probably try both a 7x7 RHCP antenna and a rotatable 7-element linear antenna to see which works better.  Maybe I will find that a linear antenna can be consistently rotated to be as good or better than a RHCP antenna.  Maybe I will never achieve good VSWR with a homebrew RHCP phasing/matching harness.  Or maybe RHCP will out-perform linear most of the time, with no fussing over polarization.

Wayne Estes W9AE
Mundelein, IL, USA

p.s. Due to the poor off-pointing angle and other near-term commitments, I'm thinking of an AO40 holiday expedition to Guadelupe (FG) in January or February of 2003.  That would give me plenty of time to assemble and optimize the portable setup during the summer and take it on a "practice trip" to the AMSAT symposium in November.  Maybe AO40 will be using 3-axis stabilization by then.  If so, the off-pointing angle would be consistently low and the entire orbit would be usable.  The intermittent nature of AO40 windows can make for a relatively balanced vacation mix of radio time, beach time, and jungle hiking time.  That's MY idea of balance, anyway!   : )

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