Norman, The TPM II is a low-gain beam antenna (2 element, about 6 dBi) using a full wave loop for the driven element. It requires an azimuth rotator to be effective, but because of its low gain does not need an elevation rotator. It can be configured with a coaxial relay for switching polarity (not required). I found this extra feature invaluable for the LEOs like AO-27, UO-14, and FO-20. I have not had them up since AO-51 and SO-50 have been in orbit, so cannot comment on the current need for polarity switching except that AO-51 in mode V/U does seem to "swirl" like UO-14 when I worked it mobile/portable with a hand-held Yagi antenna.
A QHA is an omnidirectional antenna with a circularly polarized pattern that is generally superior to that of eggbeaters (their patterns are linear at the horizon, only circular overhead and mixed in between). Another choice in omni antennas is AA2TX's parasitic Lindenblad antenna presented at this year's AMSAT Symposium in San Francisco. Getting a copy of the proceedings is worth it just to see this innovative design.
A beam antenna, like the TPM II, will always be superior to an omnidirectional antenna. The beam needs a rotator and the omni needs a preamp (at the antenna) to be effective. If you go with a larger beam, anything more than 3 or 4 elements, you will likely need an elevation rotor as well, but this is a configuration more suited to HEOs than LEOs.
73, Jerry, M0GOE
----- Original Message ----- From: "Norman W Osborne VE3CJE" [email protected] To: [email protected] Sent: Friday, November 17, 2006 5:09 PM Subject: [amsat-bb] Comparison Quadrifiar verses TMP ll
Just wondering, how the comparison of Texas Potato Mashers ll verses the Quadrifilar Helix for Leo's. Both with the ability to switch RHCP and LHCP
Norman.
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