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Author Topic: Ground plane for a mobile antenna ?  (Read 1697 times)
XYZ234
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Posts: 82




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« on: October 28, 2006, 05:03:26 AM »

I have an extra mobile antenna that I'm going to mount outside on my garage. It's a 5/8 mag mount with about 15 feet of coax. I'll use this to connect to my handheld to use when I'm working in the garage. My question is what should I build for a ground plane ? I do alot of welding in my garage and have all kinds of scrap metal I could use. What ever I make I'm going to weld to a peice of 5 foot pipe and bolt it to the peak. What size/shape ground plane should I make, I haven't got a clue.
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K0BG
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« Reply #1 on: October 28, 2006, 05:45:17 AM »

A few pieces of welding rod about 18 inches long will work fairly well. Of course, if you have a chunk of metal 18 inches square, all the better.

Alan, KØBG
www.k0bg.com
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XYZ234
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« Reply #2 on: October 28, 2006, 05:54:30 AM »

I can quickly weld together a couple peices to make it 18 inches square. Is that the best size, 18 x 18 inches ?
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XYZ234
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« Reply #3 on: October 28, 2006, 06:21:27 AM »

Also does it have to be 18 inches square solid ( like a solid sheet ) or can I just use some angle iron or flat bar and build a frame 18 inches square with a few pieces running across the centre ( with lots of open spaces ) and mount the antenna in the center ?
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K0BG
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« Reply #4 on: October 28, 2006, 08:08:02 AM »

It doesn't have to be solid. Technically, the radials should slope down to maintain the input impedance at 50 ohms. However, the mag mount adds a little loss, the SWR is going to be low anyway. Just stick it on what ever you have. A little larger is okay, but smaller isn't.

Alan, KØBG
www.k0bg.com
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XYZ234
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« Reply #5 on: October 28, 2006, 09:27:45 AM »

Done, I just cut 2 18" lengths of 2" wide flat bar 1/8" thick and welded them side by side, wide enough to stick the magmount onto. Then I just welded that to a 4 foot piece of pipe and bolted it to the peak, works good, low swr. I can hit a few repeaters roughly 100 km's away on 1/2 a watt with the hand held ( which I use with a speaker mic, the simple man's base set ) just like that. Thanks for the quick advice. 73's.
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KI6ETL
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« Reply #6 on: November 01, 2006, 11:36:30 AM »

I haven't tried it myself, but I've been told that you can just use something like a cookie sheet or a pie pan.

Dave (KI6ETL)
http://www.ki6etl.org
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KG4RUL
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« Reply #7 on: November 02, 2006, 04:27:31 AM »

If I turn my head to the right, I can see my magmount 2M antenna setting on a cookie sheet.  Works fairly well with my iCOM HT.

Dennis KG4RUL
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WB4QNG
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Posts: 362




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« Reply #8 on: November 06, 2006, 05:00:18 PM »

I got a couple setting on coffee cans. They work.
Terry
WB4QNG
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