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Old 10-07-2011, 05:03 PM   #1
KE5ZRT
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Lightbulb 2m Ground Plane (my design)

I had some junq lying around and I wanted to build a 2m ground plane antenna for one of our local technicians. I scoured the internet and found a lot of plans but I wasn't satisfied with any of them. Many plans using an SO-239 didn't include any means of fastening to a tower or mast. Others had poor bolt-on designs for the radials by looping the radial around a single bolt to fasten them to the SO-239. It seemed to me that this method would work loose over time. So, I scratched my lumpy head and set out to make a better design.

First, I cut a piece of 1.5" x 1.5" aluminium angle to 1' length and rounded the corners using a quarter as a template for aesthetics and safety.



Second, I marked and drilled holes for a mounting u-bolt that I had in my junq box.



Third, I marked and drilled holes for the SO-239 socket.



Fourth, I cut four radials at 20 5/16" from some stainless steel scrap whips I had been saving. Any number of materials can be used for this such as: welding rod, coat hangers, ground wire or stripped romex. Then I sandwiched the radials between the SO-239 and the aluminum angle as pictured below.



Finally, I cut a vertical radiator at 20" from some scrap heavy gauge ground wire. I filed the end of the ground wire until it fit into the SO-239 center conductor and soldered it in place. (Not shown) Then, I sealed the soldered connection using grey RTV sealant--silicone will also work for weather proofing.



To finish the project, I will use an antenna analyzer to tune the antenna by trimming the radiator and radials 1/8" at a time until my desired resonant frequency of 146.520 is acheived.



This is a cheap, effective and easy homebrew project for 2m. It can be modified for any frequency. I believe this design will prove to be more durable and easier to mount than others that I have seen.

73 de KE5ZRT
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Old 10-08-2011, 10:37 AM   #2
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Good work!

Now you have a "union of dissimilar metals" where the stainless meets the aluminum. Suggest a liberal application of RTV/silicone seal under the PL-259 flange.

SWR on this type antenna can be adjusted by bending the radials downward, changing the distance/capacitance between them and the radiator. Way easier to do with copper wire than SS whips, though!
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Old 10-08-2011, 10:41 AM   #3
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Great job Chris! Nice club project also!
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Old 10-09-2011, 07:01 PM   #4
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Thanks Radio!

Initially, with rhe radials straight, the antenna was resonant at 154.000 mHz with a SWR of 2:1. I freq'ed out and soldered a 6" extension on to the vertical and bent the radials to 45°the based on your advice. Then I ended up trimming the vertical radiator back to the original length and achieved a resonant frequency of 146.000 mHz with a SWR of 1.5:1 at 50 Ohms. Just for the sake of experiment, I rotated the radials 1/4 turn, reducing the angle to about 22.5° which resulted in a SWR of 1.2:1 @50 50 Ohms.

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Old 12-28-2011, 09:08 PM   #5
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Be careful about the silicon. Some of it will affect your SWR and will chemically affect your connection. Test a cured blob of it in your microwave and if it gets hot don't use it. Most of the urethanes work as well - Like Shoe goo or Goop. But.... test those too.
I used a clear silicon on my 432 antennas without testing them and ended up having to peel it all off - a time consuming job.
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Old 12-29-2011, 11:43 AM   #6
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That is actually a good design.. If you angle the radials down a bit (I"m not sure the exact angle without checkign) you will get a better match to 52 ohm coax, as it is it's 35 ohms.
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Old 01-02-2012, 05:49 PM   #7
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Hi Chris, nice implementation of a grand ole standby!

I recently ran across a neat alternative to the ground plane - the J-Pole - which you might find interesting in your emergency work.

http://www.larrywatford.com/pdf/JPole.pdf

There are a lot of implementations of this design as well, including a piece of twin lead hanging from a tree limb, but the design attached is very similar in hardware to what you did with the ground plane.

I've built several of these for various applications - it's easy to replicate with good results (no tuning) - makes a good club project for newbies.

I have one for the rv, one on the boat, one at the condo (in the attic), one at the office, and one in the "grab and go" duffel bag for emergencies.



The antenna has several advantages over the ground plane:

1. No radials required
2. Lower angle of radiation - higher gain
3. Wider Band width
4. Two bands for the price of one
5. Easy conversion to marine, aviation, and FRS freqs
6. Good performance mounted close to the ground
7. Self protecting in lightning (but not bullet proof)

I've driven mine with everything from a VX3 @ 100mw to Alinco @100 watts always get good reports.

I also put an extra threaded hole on the emergency unit to match a photo tripod screw - for a quick and dirty set up!

Also makes for a great simplex repeater (or use two for a cross band 440/144 (no duplexer) set up) - here in the mountains!


Thanks for sharing you project!
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Old 07-20-2017, 01:40 AM   #8
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That's a great little ground plane you made there. I'm trying to make something like this myself.
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Old 07-20-2017, 03:28 PM   #9
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Welcome aboard Carnes!

I have made several of these type antennas over the years for improving HT communications for ARES work.

Feel free to stomp around like you own the place. Everyone else does.
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Old 08-21-2017, 10:14 PM   #10
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[QUOTE=Radio;8834]Good work!

Now you have a "union of dissimilar metals" where the stainless meets the aluminum. Suggest a liberal application of RTV/silicone seal under the PL-259 flange. QUOTE]

Stainless and aluminum are very far apart on the Galvanic chart, and are chosen for this property on thousands of solar electric systems around the world.
Nothing to worry about in our lifetimes.
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