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Re: Disparaging Helical Antennas for AO-40...some notes




Zack,

Thanks!  I pulled out my Sept. 97 issue of QEX.  Good info for a helix with
cavity reflector.

Also interesting how your predictions for P3D are now being seen.
Especially found your comments about ground noise and foliage blocking
pertinent.  Yesterday morning I attempted to listen to the AO-40 S2 beacon
shortly after AOS.  The problem is that the dish is looking thru the trees
at elev. <10 degrees.  Previous observation of AO-40 with the 4-foot dish
when elev = 30 degrees produced a signal three s-units over noise [guessing
~12 to 15 dB].  The noise floor looking at the trees was S-3 vs S-2 looking
at cold sky.  My Drake converter NF~6 dB.  Its curious  that filling the
dish aperture with 290K "hot" trees produced about 3 dB more noise [a NF of
3 dB is equivalent to 290K]!  BTW the beacon was not heard :-)

Ed


>From: "Lau, Zack,  W1VT" <zlau@arrl.org>
>My September 1997 QEX column (the issue with a cavity reflector helix on the
>cover)
>suggested gains of 15.5 dBi for the G3RUH helix and 17.8 dBi for an accurate
>duplication
>of the King and Wong 35 turn helix.
>
>I concluded that you really want a small dish on  for 2.4 GHz receive.
>However, if you have
>a really fine converter with an EME quality preamp, it should be possible to
>use a helix.
>--Zack W1VT
 

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