Topband: Radiation Resistance

[Chortek, Robert L.]

Hi Dave,

Thanks for the reply.

The antenna is fed at 3’ off the ground.   The radials slope up at about 45 degrees to the roof (at about 10’).

It’s resonant at about 1.9 MHZ so I use about 2 turns of a 5.5” diamanté’s coil made of very heavy gauge copper wire.

I’m using an 1 to 1 Balun Designs isolation transformer at the feed point and a 32/50 UnUn to match the impedance of the coax. Another isolation transformer is used at the shack.

Thanks for your input!  Much appreciated

Bob
Robert L. Chortek

On Mar 7, 2020, at 11:39 AM, Dave Cuthbert <telegrapher9 at gmail.com> wrote:



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Robert, some questions:

Does the 55 ft vertical begin 10' above earth for a total radiator length of 45 ft?
What frequency?
The 45 deg angle doesn't work with the length and radial end height.

At 1.83 MHz a 55' radiator/top wires with the base 10' above earth, and eight 67' radials at 10 ft, the radiation resistance is 8.7 ohms. I believe it should measure closer to 9 ohms than the 29.7 ohms you measure (implying GND loss of 21 ohms). Are the radials decoupled from earth GND with a high-Z feedline choke? I'm using EZNEC the NEC-2D engine.

For a 45' radiator/top wire with base 10' above earth and eight 67' radials at 10' the radiation resistance is 5.3 ohms.

    73, Dave KH6AQ

On Sat, Mar 7, 2020 at 8:59 AM Chortek, Robert L. <Robert.Chortek at berliner.com<mailto:Robert.Chortek at berliner.com>> wrote:
Good Day!

Does anyone know the radiation resistance of a 55 foot vertical #12 wire, top loaded with 2 41 foot #14 wires sloping at 45°, with their ends at 35 feet?

I’m curious about the efficiency. The fee point impedance is 29.7 ohms, and I’m using eight 1/8 wave elevated radios at 10 feet.

Please and thank you!

Bob
Robert L. Chortek
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