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Re: New Observations on UO-14 (17:00UTC Pass)



Howard and David,

"Howard Long" <howard@hanlincrest.co.uk> writes:

> Yes, the eggbeaters aren't too hot at low elevations especially if you have
> radials fitted unless you perform some sort of rotation such as Jerry's
> devised. As Jon said, limited to predominantly linear polarization at the
> horizon also gives you even less chance as there is probably a strong linear
> component from the sat at low angles. Murphy's law probably states that
> it'll be in the opposite polarization to you too. Again, tilting and
> rotating would help here.


Howard & David,
Please allow me to comment on the omni antennas and offer an explanation to those not familiar with the references...

The first antenna for many home stations are omnidirectional circularly polarized antenna.  The most common of these is the M2 eggbeater.  You can also build a popular version of this antenna, but I have found them to be ineffective at low elevation passes (most passes are below 45 degrees 90 percent of the time), especially if equiped with the radials option and as noted in David's previous posting.  An improved version of this classic design, the Eggbeater II, will give pretty fair results from horizon to horizon as it is designed to concentrate it's gain pattern at the horizon and not into the sky.  I took one of these to Russia with me and worked all the LEOs and AO-10 with it.  The basic Eggbeater II design is fixed right-hand circularly polarized (RHCP), leaving it susceptible to the “fades” common in satellites downlink (you will not hear 100 % of the pass), but is still an effective, simple antenna—and MUCH better than the “classic” eggbeater.  Other antennas in this class are the turnstile, the quadrifilar helix array (QHA), and the Lindenblad, the latter two being considerably more difficult to build, and none of these being commercially available for the ham sat freqs (that I know of).

The next step up is to buy or build a higher gain antenna and rotate it to match the satellites' position (azimuth).  Gain in the 6-7 dBi range, corresponding to a 60 degree beamwidth, is about the maximum that can be utilized without needing elevation control.  Unfortunately, there are no commercially available circularly polarized antennas available in this size/gain range.  If you are blocked at the horizon (and up to 20 or 30 degrees), I can recommend the original Texas Potato Masher (Howard's reference in the earlier posting).  If, however, you have a good view to the horizon, then the TPM II antenna is a perfect candidate to work all the LEO’s as well as AO-10 out to about 25,000 km.  This antenna does not require an elevation rotor or even accurate pointing (you can do it manually with no trouble).  I built mine with coaxial relays to switch the circular polarity, allowing me to match the satellite downlink.  I can hear and work ALL the LEOs from horizon to horizon using this simple-to-build antenna and a TV-type rotator.  I have been using this antenna for the last year or so and have made literally thousands of contacts with is and Worked All Continents with it (AO-10, of course).

Sorry so long-winded, but I just wanted to help clarify the references and options....
73,
Jerry, K5OE
http://members.aol.com/k5oe


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