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DiPole Antenna Build


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While pursuing YouTube the other day, I came across a great video from the 2020 Virtual Christmas Summit by Jason Rasmussen called "Transmitting Your Audio Over FM".  One of the improvements he suggests is replacing the antenna that comes with the FM transmitter with a dipole antenna.  After doing some searching on some other forums, I dug up some fairly easy plans for one and made a video of my experience building it:

 

It was actually a pretty easy build and the result were better than I could have expected.

 

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I built a vertical dipole several years ago.  It works very well.  I used 3/8 inch copper tubing for the elements inside 1/2 inch PVC pipe.  Here are a few photos.  I am posting both the photos and links to the photos because some browsers (Chrome) are complaining about embedded photos from a non-secure source (my web server) on a secure page (LOR forum).

In the first photo the top of the antenna is the black pipe sticking above the back of the brick column.

FM-Antenna_1.jpg

http://www.newburghlights.org/photos/FM-Antenna_1.jpg

And a side view.  The bottom element of the antenna ends about a foot above the ground, but the pipe goes all the way to the ground to support the weight of the antenna.  And just like the year that I took this photo, the dwarf mandarin orange tree in the background, that tree is currently covered in oranges.  Another couple weeks and I get fresh squeezed OJ - yum!

FM-Antenna_2.jpg

http://www.newburghlights.org/photos/FM-Antenna_2.jpg

Closeup of the center feedpoint.  The white wire is the center conductor of the coaxial cable, and the black wire is the shield of the coaxial cable with heat shrink tubing covering it.  For each element, the end was flattened in a vice and a hold drilled.  A brass threaded rod was put through the hole in the element and nutted and then soldered.  A second nut holds the wire lug with the feed line.  What you can't see is that on the back side of the element is a piece of lexan that holds the spacing between the two elements.  So the stack on each brass threaded rod is (back to front):  nut, lock washer, lexan, nut, copper antenna element, nut, wire lug, lock washer, nut.  Note that the copper tubing came rolled so I had to straighten it out.  No need to do a perfect job as a little bends makes it stay put inside the PVC pipe.

FM-Antenna_3.jpg

http://www.newburghlights.org/photos/FM-Antenna_3.jpg

And how it is mounted.  When I built the brick column, I installed a single gang electrical box with conduit into the interior of the column.  Note that the upper and lower PVC pipes are 1/2 inch, but the conduit T is 1 inch with reducers.  Makes far more working room inside!

FM-Antenna_4.jpg

http://www.newburghlights.org/photos/FM-Antenna_4.jpg

 

 

 

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Me I would be cautious using a larger antenna on a part 15 fm transmitter. With the risk of transmitting further than you should. Wouldn't want a visit from the Friendly candy company (FCC). 

I do like K6CCC's plans though for the antenna, might have to use a modified version of that for ham radio. 

Edited by TitusCarnathan
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