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Re: UO-22 azimuth-only system



John, Bob, et al.,
This discussion is right on the mark for what is needed by many newcomers to satellites.  Bob has suggested many times a simple azimuth-only tracking system would be perfect for a lot of hams.  I continue to be amazed no one has latched onto his simple design for the RS rotor interface and marketed a plug-and-play $99 satellite tracking system complete with Bob's "freeware."  Heck, I have two of those rotors sitting in my garage collecting dust!

What I did want to comment on, though, was the issue of polarity (no one has mentioned it).  Using low-gain antennas, i.e., wide beamwidth antennas, leaves little margin for polarity mismatches with the signals arriving from space.  If these types of antenna are to be used AND if you also want to hear 100% of a LEO pass, you must be able to switch polarity to match the satellite's signal's polarity (changing all the time).  Otherwise, you can easily spend a lot of time listening to static.  This is, ultimately, the failing of most omni antennas--they hear great one minute and are deaf the next when the satellite's signal polarity changes to the opposite of whatever the antenna is.  This is also, in large part, what makes the Arrow Antenna so effective.

Several years ago I designed and built a couple of antennas for this exact LEO scenario.  The second one, dubbed Texas Potato Masher II, worked exceedingly well, giving me WAS (including both KH6 and KL7 from Texas on FO-20) and VUCC.  It is a simple design, based on a full-wave loop driven element and a reflector--much like an eggbeater--except it is designed for maximum forward gain (6.7 dBi) and is thus pointed at the horizon (60 degree E-plane beamwidth).  You can see it, along with simple construction information, at (select TX Potato Masher II):
http://members.aol.com/k5oe

I designed it with polarity switching in mind and used a pair of coaxial relays to independently switch the 2 m and 70 cm antennas.  I could copy all the mode J LEOs from horizon to horizon without fades.  Of course, I also had a 70 cm preamp on the mast (25 m of coax to the shack).  I even worked AO-10 regularly when near perigee and have Japan and many European contacts in the log as well.  I only took them down and put up bigger antennas when I wanted to work AO-10 more seriously and at the same time get ready for P3D (now AO-40).

Why did I build them?  Because I did not want to spend $500 for an az/el rotor AND because nobody makes small satellite antennas for the beginner, the apartment dweller, or the stuck-with-deed-restrictions ops (like me).  Still true today, unfortunately.

Sorry for being so verbose.  The point of all this?  Azimuth-only control for LEOs is more than adequate with low-gain antennas.  Low gain antennas, however, will leave you with lots of "fades" unless you have the ability to switch polarity to match the satellites'.  For UO-22, not a big deal because you just ask for another DIR.  For UO-14, FO-20/29, etc., you will hear portions of the pass as static.  The very last thing we need is more operators on UO-14 who can't hear the satellite.
73,
Jerry, K5OE

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