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My home brew gmrs slim Jim antenna

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Thetoulman

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Dec 27, 2011
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Just wanted to show off. It's mounted in my attic. It has a 1.2:1 swr across the gmrs band, and around 2.0:1 on the upper end of 70cm band. Seems to work better than the simple ground plane it replaced.
 

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Thetoulman

Member
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Dec 27, 2011
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I do transmit with it, with very good results.

As far as measurements go, this is what I used.
http://www.m0ukd.com/Calculators/Slim_Jim/

I used 465 as the frequency (median between simplex and repeater inputs).

It's all type M copper pipe and standard elbows.

If I were to do it over I would use the same measurements but instead of measuring center to center on the copper pipe, I would measure the distances between the closest edges of the pipes. I found the feedpoint measurement from the calculator to be way off from acceptable swr; this could be from the center to center measurements, or the de-tuning of the antenna by adjacent metal in my attic.

Scuffing up the pipe with sandpaper helped make a better connection at the feed points under the hose clamps.
 

Thetoulman

Member
Joined
Dec 27, 2011
Messages
17
One other thing of note on this project:

When this antenna is fed with rg-58 coax ~50 feet the distant gmrs repeater I built the antenna for is unreachable. With lmr-400 the same repeater reads s3-s5. So if you are looking for a high performance antenna system, don't skimp on the coax.
 

KD0WFZ

Newbie
Joined
Aug 4, 2013
Messages
1
Feed line

The method you used for your feed line, can that in turn be used on cactus style j-pole?
 

dksac2

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Joined
Apr 18, 2012
Messages
327
Location
Idaho
You also need a balun with a J pole, they radiate off the coax like crazy, and yes, do use LMR-400.

John KF7VXA
 
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