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Author Topic: CP Antenna design....  (Read 1157 times)
KD0OCY
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Posts: 17




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« on: March 10, 2013, 09:56:45 AM »

So I have been reading up a bit on circularly polarized antennas preparing plans to build one of my own and am thinking about building the following....

1 loop antenna with a vertical fed 90 degrees out of phase.  Sort of a different approach than the egg beater and the turnstile antennas I have come across. 

Any thoughts on how (or if) this might work? Suggestions?
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W4OP
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« Reply #1 on: March 10, 2013, 10:58:28 AM »

What type of loop antenna. Halo/squalo designs are typically 5-6dB "out of omni" and radiate from the mast and coax- both solvable problems but must be paid attention to.

Dale W4OP
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WB6BYU
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« Reply #2 on: March 10, 2013, 02:11:52 PM »

For circular polarization both components have to be matched in amplitude and have the proper
phase shift in each direction.  I don't think either will work when combining a horizontal loop
with a vertical antenna.

What short of pattern are you trying to achieve?
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KD0OCY
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« Reply #3 on: March 10, 2013, 06:36:53 PM »

Wanting a pattern that will hit satellites well.  I'm guessing that since they are two very different antennas with different gain and radiation angles, it might not work that well. Especially if the sat happens to pass directly over me. 
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N6EY
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« Reply #4 on: March 10, 2013, 09:57:28 PM »

An eggbeater, quad helix or a turnstile will work just fine.

Linear polarization will work fine with most LEO birds, given a little extra gain to overcome the 6 dB loss between CP and linear polarization.

The vertical/loop approach, as pointed out, will yield weird results if a CP feed is attempted.  It might work okay to switch between the two. 

Switching between a vertical, with a low angle of radiation, and a horizontal omni (HO Loop) at .1-.2 wl above a ground plane, will give you good coverage at nearly all angles. 


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________________________________
73,
Jason N6EY
________________________________
WB6BYU
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Posts: 13139




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« Reply #5 on: March 11, 2013, 09:10:00 AM »

Quote from: N6EY

... extra gain to overcome the 6 dB loss between CP and linear polarization.




Only 3dB, actually.




Quote

It might work okay to switch between the two. 



That may be the best solution.  You can use a rotatable beam for best coverage
near the horizon where signals will be weaker, and a CP omni for when the bird
is overhead.
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