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homemade riser/extension

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Old 12-01-2011, 06:59 PM
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Default homemade riser/extension


For those who need a riser/extender for whatever purpose, whether to get your mobile antenna coil above your truck cab, or simply to get it higher, one method I've used is

as easy as a trip to the local Home Depot for some brass fittings, a 3/8-24 x 1-1/4" bolt, and a tube that is of 5/8" outside diameter. Cut your tube of any length you

desire and put the parts together. One thing to note is the 1/8" x 1/2" brass bushing must have the 1/8" thread reamed out with a 3/8-24 tap before it will receive an

antenna or the 3/8 x 1-1/4" bolt.





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Old 12-02-2011, 05:29 PM
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As an example, here is an antenna load from Radio Shack that requires a 57" whip and is normally bottom loaded. Putting it on the riser required a shorter whip, but not a direct trade off. The over all length of the antenna with the riser under it is 80". According to the MFJ-209, I have a 1.5:1 bandwidth from 27.815 to 26.515 with it up there. And it seems to work well with both local and DX contacts.

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Old 12-02-2011, 05:33 PM
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nice

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Old 12-02-2011, 07:31 PM
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Thanks, Mack.
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Old 12-02-2011, 07:32 PM
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Someone asked me this/;

Quote:
Any thoughts how i can put a whip adjuster on the top of the riser to raise and lower a 102?


Maybe I would if I had some idea of why you'd want to do that. To change the resonance so it can be used on other bands, or just to clear obstacles like a low garage, etc.?

I've been drilling a hole in the top nut on the bushing and threading it with a tap in order to put in a set screw for whip length adjustment.
If that is the idea, you do that and slip the bushing over the whip before you screw it into the top of the extension. Before that is done, a rubber seat for a faucet is placed around the whip in order to keep it centered as it is moved up and down the tube. When you've found your tune, tightened the set screw for the frequency range you are working.
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Old 12-02-2011, 08:59 PM
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5/8" od or 3/8 od?

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Old 12-02-2011, 10:10 PM
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The tube is 5/8" OD
The bolt is 3/8" diameter with 24 threads per inch
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Old 12-03-2011, 09:31 AM
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Quote:
Originally Posted by HomerBB View Post
Someone asked me this/;





Maybe I would if I had some idea of why you'd want to do that. To change the resonance so it can be used on other bands, or just to clear obstacles like a low garage, etc.?

I've been drilling a hole in the top nut on the bushing and threading it with a tap in order to put in a set screw for whip length adjustment.
If that is the idea, you do that and slip the bushing over the whip before you screw it into the top of the extension. Before that is done, a rubber seat for a faucet is placed around the whip in order to keep it centered as it is moved up and down the tube. When you've found your tune, tightened the set screw for the frequency range you are working.
Conduit with weather tight fittings would do nicely as a slider or a low power gamma match with an adjustable tapping point

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