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The NA4IT 'CHEAP' Dual Band Ground Plane

Created by Scott Duckworth, NA4IT on 2021-07-10

"Editor's Note: Due to the popularity of some of eHam's older articles, many of which you may not have read, the eHam.net team has decided to rerun some of the best articles that we have received since eHam's inception. These articles will be reprinted to add to the quality of eHam's content and in a show of appreciation to the authors of these articles." This article was originally published on: 12/03/2003

 

The NA4IT "CHEAP" Dual Band Ground Plane Antenna

Here is a neat little antenna that is very easy and cheap to build. It is ideal for Technician class hams needing a "first" antenna, and also a very good "emergency" antenna for use during Skywarn events when you don't want to be on the sky hooks tall in the sky! This little antenna is very functional on 2 meters and 70 centimeters.

 

Materials needed:
(1) SO-239 4 hole chassis mount connector
(3) 3/32 bare welding rods (copper or brass)
Rosin Core Electrical Solder
Clear Silicone Sealant

Tools Needed:
Heavy duty soldering gun
Wire cutters
Vise or "Third Hand" or another human.

The finished product will look like this:

 

0x01 graphic

 

Let's get started! From the welding rods you need the following:

(1) piece 25 & 1/8 inches long
(2) pieces 6 & 1/2 inches long
(2) pieces 19 & 1/2 inches long

 

Here is how to prep the SO-239 connector:

0x01 graphic

 

Now to make the vertical element:

 

0x01 graphic

Now take the 19 & 1/2" on one end, placing each on into one of the mounting holes of the SO-239 and crimp it tightly, then solder, filling the hole. The arraingement should look like this:

0x01 graphic

Here is a close up photo of the first one I did: (My 6" radials were made from a welding rod 12 12 & 3/4" long bent into a "C" shape and run down through 2 of the mounting holes, then bent back out to the proper angles and soldered.

 

0x01 graphic

Finish by covering the entire center pin and insulator area on the "top" of the SO-239 with Clear Silicone Caulk.

To mount the antenna, use a 1-foot piece of PL-259 connector up through the piece of conduit, connect the antenna to the coax, and let it sit down into the conduit. Use stainless steel hose clamps to attach it to a mast. I'm sure you can come up with other ways to mount the little antenna also. This antenna makes a great Severe Weather antenna, so that you can maintain communications, by mounting it in the attic or even below the eaves of your house.

The first time this one was used, it was used at a RACES drill. It was mounted to a small telescopic speaker stand by clamping the PL-259 to the stand with a single hose clamp. It was inside the building, and with 10 watts, we could hit both 2M and 70cm repeaters up to 30 miles away (and that's in East TN, the "Heart of the Smokies"!).

SWR results of the prototype were less that 1.5-1 on across both bands with 55 watts input. Your results may vary. Also, this antenna may be somewhat directional. Experiment with it. I would welcome computer-plotting results if some one would like to do them. Let me know how it works for you!

NA4IT, Scott Duckworth
na4it@arrl.net

 

KJ4DGE2021-07-14
The NA4IT 'CHEAP' Dual Band Ground Plane
Saw this on another site and have been wanting to make one for a while. Thanks for the post!

Greg-KJ4DGE