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Turnstile antennas for mode A

Ladies and gentlemen of AMSAT,

I am currently installing a ten-meter dipole in my attic for, among other
things, mode A work.  I was wondering if the "turnstile" for 10m receive is
worth the trouble (not MUCH trouble but if it doesn't buy me anything i'll
save the coax)?  Will this configuration significantly improve receive over
a standard dipole?  For terrestrial work, what will be the impact on transmit?

Finally, a question for the RF-impaired:  Davidoff's Handbook calls for a
1/4 wave phase delay line between the two turnstile dipoles- a 90 ohm
line...why 90 ohm and how critical is this (ie would 50 or 75 ohm work?
Not that I have a problem buying 10 feet of coax... just curious on the
sensitivity of the application)?

Thanks for the help,


PS  Other than listening to a couple of the RS birds on a shortwave I have
NO experience working any of the satellites- this will be my first foray.