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Need help selecting FM aerial
Need help selecting FM aerial
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Old 9th May 2006, 06:08 AM   #21
DigitalJunkie is offline DigitalJunkie  United States
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Join Date: Apr 2003
Location: Portland,Oregon
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I thought the J-pole was an end-fed 1/2 wave,using a 1/4 wave matching section? meh,what do i know..

I originally built it to use with an FM transmitter,so I used that and my SWR meter to tune it to ~98Mhz. It worked fairly well on my transmitter,maybe a bit more range than the 1/4wave ground plane I had up..
I'm not sure how critical tuning is for recieving,cause mine was basically already tuned for me.. It sure works well though!

I used a couple copper pipe clamps for the feedpoint,with a couple (equal length) pieces of 12awg solid wire around the screws,to a SO-239 (??) connector in the center.. I suppose you could just solder the coax right to the pipe,if you know the feedpoint distance.
I added a choke in the coax,about 4-5 Turns.. -it didn't seem to make much difference in transmitting,or recieving? I'll leave it there anyways for peace of mind.

Another tip..cut the vertical parts a bit short- In the pipe-ends (caps) on the top of the vertical sections I drilled a hole in the center,soldered a nut on the *inside* of the cap,and cut off a small piece (6 inches) of threaded rod to screw in there,and I put a nut on the outside,as a "keeper" this way the top couple inches of the antenna is adjustable in length,so you can get it tuned *just right*,and tighten down the outter nut to hold everything in place.
Otherwise you'll have to cut/add pipe to tune or retune it
(maybe not such a big deal for RX? But,it's a pain when you change your TX freq. alot.)
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