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[TowerTalk] Full wave loop on 80m : Impedance 50 or 75 Ohms??

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Subject: [TowerTalk] Full wave loop on 80m : Impedance 50 or 75 Ohms??
From: (Jon Ogden)
Date: Tue Jan 28 07:52:05 2003

Dug out an old textbook from my antenna class in college (Antenna Theory and
Design by Stutzman and Thiele).  On page 250 of the book they are discussing
full wave loop antennas.

"The square loop antenna is most useful in practice for a one-wavelength
perimeter becuase of the desirable input impedance properties.......The
input resistance for a one wavelength perimeter is about 100 Ohms."

Unless I am reading something wrong, it appears that 100 Ohms is your

The antenna with the impedance range between 50 and 75 is the dipole.  A
resonant half wave is about 70 Ohms.

Now, I forget what happens to the impedance when parasitic elements are
added as in a Quad.

If I am incorrect, I am more than willing to be corrected!



on 1/27/03 9:15 PM, Lee Noonan at wrote:

> I have been using Full wave loops on 80m since 1987 and have always used 75
> Ohm coaxial cable as feedline without a Balun.  I know of other hams that use
> a Balun on a full wave loop. My Loop is Rectangular in Shape and fed in the
> center of one of the shorter sides. The Antenna is terminated with a gap of
> around 3 inches between the ends.
> This was how it was described , for a German Quad antenna which is a Full wave
> loop in a Diamond shape terminated at one of the sharp pointed ends..The
> German Quad was Quoted with an Impedance of roughly halfway between 50 & 70
> Ohms Impedance.. My Quad antenna is 33 feet high at all 4 points.  Any
> Comments on what impedance this Antenna May be at the feed point and how to
> feed it with Coaxial cable... I am about to run ALL new cables thru the roof
> of My House and I'm wondering whether to use 50 or 75 Ohm Cable...

Jon Ogden
NA9D (ex: KE9NA)

Citizen of the People's Democratic Republik of Illinois

Life Member: ARRL, NRA
Member:  AMSAT, DXCC   <- Updated on 1/22/03!!!

"A life lived in fear is a life half lived."

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