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AMfone's Online AM Handbook => Antennas => Topic started by: WU2D on July 02, 2006, 06:50:52 PM

Title: 20M 5/8 Groundplane
Post by: WU2D on July 02, 2006, 06:50:52 PM
Here is a simple afternoon antenna project. Get out your Slingshot, Fishing Rod or Bow.

I wanted to try a simple vertical to pull up into a tall tree in the backyard to try for some low angle 20M DX. I have a 100' chunk of buried low loss coax going out there which allows me to play with antennas in the woods.

I used the following formula for the 5/8 radiator: 585/f  (Frequency in MHz)

This gave me a vertical wire of 41 feet. I then simply cut 5 radials to 16.5 Feet.

The radials and the feed were at 10 feet off ground and the radials were essentially horizontal. I clamped on a couple of big ferrites on the coax at the elevated feed.

The match to 50 Ohms is not so good as you could imagine. The impedance is something like 75 Ohms Real and - 450 Ohms Capacitive, so you need some series L to match it.

I did not go crazy with the match. I simply made a coil out of copper tubing 10 turns at around 3 inches diameter with about 1/4 inch between the turns. I stuck a big alligator clip on the center of the coax. It turned out to require 7 turns to get a very nice match. This coil was insulated with standoffs and screwed into a tree.

It really brings up the DX compared to my 260 ft longwire (which is my main antenna), which is the point. Local stations go away.

Mike WU2D

Title: Re: 20M 5/8 Groundplane
Post by: k7pp on December 10, 2013, 04:57:53 PM
I made this video a while back using a "Zero 5" 3db 20 meter only vertical with four tuned radials at about 20 feet and compared it to a half wave dipole at 35 feet and pointed to favor a remote receiver about 300 miles South of my QTH.
The remote receiver uses a vertical antenna and is programmable from the net.  
Here are the results.

Pete, K7PP
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands