On Sun, 23 May 2004 08:14:41 -0700, "Keyboard In The Noise"
wrote:

Golly Gee -- what happened to the great R7 radial debate ??? (:-(

Not one single reply to the excellent post below -- guess it did end the
argument (:-)

Well, I found it interesting that the R7 is a 3/8 wave antenna, not a
1/2-waver. Which means radials might work as well as those 2-meter
whips/decouplers sticking out at the base.

Funny, I've never seen Cushcraft refer in their ads to their designs
being "1/2 wave." Maybe that's just a myth somebody started...

Bob
k5qwg



Thanks for the post Tom
-------------------------------------------------------

"Tom Ring" wrote in message
Ok, I spoke to the designer this evening, and I'll pass on what I
learned. He was speaking fast, as he normally does, so I'm sure I
missed a lot. Roy can confirm that, and Roy can confirm that he handed
over another copy of his software to him just last week.

Per the designer

The R7 was built because he needed a multiband antenna in the fall of
90. The R5 was used as the base idea for the design. He worked on it
over late fall and winter 90/91. The antenna project was up and down 2
to 3 times a day at times.

The owner of Cushcraft heard of the backyard project in spring 1991, and
"asked" that it be brought to work. Tomorrow at the latest.

The antenna is not a half wave antenna, it is about a 3/8 wave antenna.
The impedance is approximately 250 ohms, and a roughly 4.5 to 1
transform is done. There is a series cap of 41 pF for 40m.

There are 7 radials of 49 inches, because Cushcraft had tons of 49 inch
5/8 whips for 2m. The R5 had 4, this needed more.

There is a false resonance on 75m or 80m, and if you put power into it
at that freq, you will burn up the matching system.

And, to end this argument, do not ever add radials to the system, and do
not remove any of the ones it comes with. It's a touchy match.

tom
K0TAR