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A Different Kind of Antenna
21 November 2011 | by 
My latest antenna project turned out very well. I took it to the beach for an on the air test this afternoon. This magnetic loop antenna tunes from 40 meters through 15 meters. In my haste to get to the beach, I forgot my antenna analyzer. After setting up the Mag Loop, I turned on the radio, turned the volume up full blast, and tuned the antenna for the loudest noise. Bingo!!
I was on the air. It couldn’t have been simpler.
The antenna is made from 3/8 inch copper tubing, 1 1/2 inch PVC pipe and a few odds and ends from Radio Shack. The heart of the antenna is an air variable tuning capacitor, 11 to 300 Pfd. The large loop, (the main loop) is fed with a half Faraday feed loop. All the information for building this antenna is readily available on line and partially from the ARRL antenna hand book.
Good links for Magnetic Loop builders: http://aa5tb.com/index.html,
http://groups.yahoo.com/group/CW-QRP-HOMEBREWERS/,
http://groups.yahoo.com/group/MagneticLoopAntenna/messages
My next Mag Loop will be 5.5 feet in diameter and made from 5/8 inch copper tubing. More on this as it develops!! There was an unexpected bonus in the speed and ease of setting up an antenna for portable use. I was on the air in minutes after getting out of the truck.
Please feel free to contact me if you are interested in building one of this fantastic antennas. The antenna has a very high Q so it has a steep tuning notch.
If you use a Faraday loop to feed it, it will be very directional. You can also use a Gama match instead of the feed loop, to feed the antenna. How did it work? I made a very nice contact on 15 meter CW with a ham in Milwaukee this afternoon. Not bad for 5 watts, an small antenna for a contact from Florida. The QSO ended with air boat QRN! The air boat passed by close to shore and I was on the water’s edge about 100 feet away. Next time I’ll bring the Bose noise cancelling headphones!!
De AA1IK
Ernest Gregoire
Geezer in the park
2 Responses to “A Different Kind of Antenna”
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What was the overall circumference and diameter? I see you have a dual gang 365pF cap, were you running then in parallel for over 700pF total capacitance?
Looks like a cap/reduction drive from the Xtal Set Society at midnightscience.com. I have several of their air variable caps, and they are good for QRP magnetic loops! The reduction drive is a necessity for tuning. Great post thanks for sharing!
Joe, the capacitor is 11 to 310 Pfd. I used only one section of the cap. The other section has a 38 to 128 Pfd value. I measured them with a cap meter.
The Mag Loop is 3 feet in diameter. Forgive me, I should have included this information in the post.
de AA1IK
Ernest Gregoire
73