Re: Comparison Quadrifiar verses TMP ll
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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Here is an idea for a cheap educational receiver kit for AMSAT/ARRL/ARISS? to provide as part of their outreach to youth:
http://www.ew.usna.edu/~bruninga/amsat-radio.html
This design uses a simple $9 FRS FM Walkie Talkie as the receiver and a -converter- kit to convert 145.800 from the Space Station to 462.5625 MHz. All of the mechanical parts in this concept total about $3 and if we can get the electronics to under $20 then this could be a great receiver kit for students to listen to the Astronauts on the ISS and Space Shuttle.
My original proposal back in October had a different mechanical arrangement:
http://www.ew.usna.edu/~bruninga/amsat-ideas.html
But this new juice-can concept solves many problems by not only providing a good mechanical housing for the device, but it also provides the IF shielding necessary to prevent any local FRS activity from bleeding through the receiver. It also improves the coupling between the converter and the receiver.
Anyway, I think this idea is a nice circuit design challenge sith lots of potential. This juice-can mechanical concept is intended to simplify some of the construction challenges for students. Can anyone design a cheap converter kit?
de WB4APR, Bob
Hi Bob,
You can buy a complete 2-meter dual-conversion receiver kit that will drive a speaker from here:
http://www.mpja.com/productview.asp?product=6599+RB
In quantity 5+, they are only $29.95 and in singles they are only $34.95.
This is not a great receiver but it ought to be more than sufficient to hear the ISS on 145.800.
73, Tony AA2TX
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At 02:49 PM 11/20/2006, Robert Bruninga wrote:
Here is an idea for a cheap educational receiver kit for AMSAT/ARRL/ARISS? to provide as part of their outreach to youth:
http://www.ew.usna.edu/~bruninga/amsat-radio.html
This design uses a simple $9 FRS FM Walkie Talkie as the receiver and a -converter- kit to convert 145.800 from the Space Station to 462.5625 MHz. All of the mechanical parts in this concept total about $3 and if we can get the electronics to under $20 then this could be a great receiver kit for students to listen to the Astronauts on the ISS and Space Shuttle.
My original proposal back in October had a different mechanical arrangement:
http://www.ew.usna.edu/~bruninga/amsat-ideas.html
But this new juice-can concept solves many problems by not only providing a good mechanical housing for the device, but it also provides the IF shielding necessary to prevent any local FRS activity from bleeding through the receiver. It also improves the coupling between the converter and the receiver.
Anyway, I think this idea is a nice circuit design challenge sith lots of potential. This juice-can mechanical concept is intended to simplify some of the construction challenges for students. Can anyone design a cheap converter kit?
de WB4APR, Bob
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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.
To amplify on that, for LEO's you don't need an elevation rotator for beams of several elements probablly up to 8 or more elements because 67% of all the times the satellite is in view, it is below 20 degrees anyway. It is only above 45 degrees less than 5% of the time. It is only above 60 deg 2% of all possible time, so just mount the beam up at about 10 degrees and you will get maximum gain down on the horizon up to about 40 degrees where you need it most when the satellite is far away (95% of the time). When it is above 45 degrees it is 10 dB closer to you anyway, and you can afford to be offpointed a bit.
Bob
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.
Check out the new AOL. Most comprehensive set of free safety and security tools, free access to millions of high-quality videos from across the web, free AOL Mail and more. _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings:
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Anthony Monteiro -
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Robert Bruninga