I’ve been experimenting with magnetic loop antennas of various sizes and configurations for the past year or so. They are fun to build and even more fun to use.
QRP and Magnetic Loop antennas go hand in hand for many reasons. They work well, are very quick to set up, and are bidirectional! Its nice to be able to ‘aim’ an antenna at a prospective target, like say ‘Africa’!
Copper face plate with PL 259 and Gamma Match sticking out of the side
Soldering with a plumbing torch is necessary in some places, like attaching the main loop tubing to the PL 259.
It may not look very pretty here, but believe it or not, my torch soldering skill is actually improving. The PL 259 is attached with screws and is soldered with a regular soldering iron to reduce inter component resistance. I’ve pretty much settled on the Gamma Match for a number of reasons. It’s easy to match and its easy to build. It works well too.
This T’ fitting helps to make the loop more stable, therefore easier to transport for portable ops.
What would hams do without PVC pipe?
Half inch PVC tubing bisects the mast and passes through the center of it. This three point connection stabilizes the loop and makes it much more robust. My first few magnetic loops didn’t have this feature and were a bit ‘wobbly, and bent more easily as they bounced around in the back of my truck.
This is the ‘business end’ of the Gamma Match
Using a plumbing torch, I attached this copper strip to the Gamma match from the main loop tubing.
Here is another nifty improvement
You can see the support PVC pipe passing through the center of the mast here, The black piece is a plastic pipe clamp. It is held in place with tie wraps. I try to keep the use of anything made of metal to a minimum in the center of the loop. I’m not worried about radiation patterns as much as trying to keep the overall weight of the antenna low. The smaller PVC pipe on the left is a tuning stick. It is tied to the capacitor and is very light and makes reaching way up to tune the antenna unnecessary. Keep in mind that merely approaching this antenna closely affects the SWR. Touching it certainly changes the SWR as well.
How Well Does It Work?
I got great signal reports today, and that is saying something for a high Q antenna and only 5 watts of RF
This is my favorite pavilion at Hagen’s Cove Florida.
Hagen’s Cove is about 17 miles from my home, along the shore route. Its a county park that is right on the Gulf of Mexico. This particular pavilion is only 50 feet from the water’s edge. I bring a sandwich and bottle water lunch, but it took me an hour to eat it today. I had very curious visitors asking a million questions about radio, and my set up. I also keep my QSL cards handy to pass around. Visitors really like seeing them.
There is a kayak and canoe launching ramp here. Air boats have their own launch site close by. And darn it, I forgot my noise canceling headphones today, again! Air boats pass by in only inches of water and just 50 feet away, so I can’t hear anything on the radio when that happens. I have this place all to myself during the week, but its busier on weekend as you can imagine with such a nice venue.
For more information about Magnetic Loop Antennas go to http://groups.yahoo.com/group/MagneticLoopAntenna/
Hagen’s Cove is in Taylor County Florida http://taylorflorida.com/
73 de AA1IK