[KYHAM] 2 Meter Antenna Question

Wed, 26 Jun 2002 09:50:55 -0700

Hi Bob and All,

Bob, yep that is an important point!

At Dayton, perhaps 25 years ago a demonstration of an RF sniffer using a
2-meter resonant circuit in conjunction with a small incandescent lamp was
demonstrated. The person doing the demonstration as I recall was Dr. Don
Reynolds, a West coast university electromagnetic lab professor. He had
developed a conical sleeve decoupled 2-meter antenna, which a couple of his
students then marketed as the AEA Isopole. I went home and built an antenna
and transmission line demonstration apparatus based on his RF sniffers.

If you would sense the field near the "J-Pole", a high voltage point would
be found at the end of the 1/4 wave launching section and at the end of the
antenna. A high current would be found near the base and at the mid point of
the half wave top part.  Yes, keeping the antenna away from metal window
frames and in the clear is important.

The writer developed a transmission line and antenna demonstration apparatus
that has been shown at the antenna forum in Dayton a couple of times and the
1985 Louisville National ARRL convention. I wonder if anyone remembers Dr.
Reynolds call, I think a K-zero now a SK or my demonstration. My old dog and
pony show might be a good program for Cave City. I am unable to make the
Lexington convention because of a date conflict.

I sure appreciate KD4PWL keeping this information system organized and
serving the amateurs in and around the Commonwealth.

73 Dave

David Smith W8YZ
Technical Coordinator
Michigan Section ARRL
Monroe, Michigan 48162-2943
Phone 734-242-5589
Fax 734-242-8413
Cell 734-479-4686
E-Mail: [email protected]
OR: [email protected]
Please visit our websites at:
http://www.arrl.org/sections/index.html?sect=MI
Or:
http://www.msp.state.mi.us/division/emd/staff.html

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Bob Burns K4RXR
Sent: Wednesday, June 26, 2002 3:54 AM
To: [email protected]
Subject: RE: [KYHAM] 2 Meter Antenna Question

At 01:11 PM 6/25/02, David A. Smith wrote:

>This
>provides a low to high impedance transformation, which drives the remaining
>half wavelength of single wire at its voltage feed point.

Twinlead J-poles are pretty slick antennas for portable use. I have a
couple for 2m, one for 220MHz, and one for 440MHz.

One thing to be careful about is mounting them too close to grounded metal.
As David describes, the lower quarter wave section of a J-pole is a
transformer. Any ground in the field of that transformer will adversely
affect the antenna's performance.

Bob...

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