Simple Low Power Magnetic Loop Antenna

                     The design of a low power Mag Loop is simplified by the absence of the extremely high RF voltages present in
           even  moderate powered loops. We are able to use capacitive coupling to the loop with readily available
          capacitors. My results from the start were certainly unexpected. My first two contacts were DX at QRP power
          and I ended my first loop operation with two more DX stations!

                 I had some 3/8" soft drawn Aluminum tubing I used for the loop, and it seemed to work OK. After playing
                with it in the back yard for a couple of years and having good luck I decided to try to build one that would  
                fit in a backpack. 

         This is the second version of the tuner. The first tuned 40 thru 15 OK, but tuning was really critical on the
         higher bands. I added a 33pf fixed cap in series with the smallest value variable I had at the time and connected
         both in parallel across one gang of the tuning variable. This resulted in about 8pf for fine tuning. I used LMR400
         for the loop. It is stiff enough that only one support is necessary.

            
          The Loop works well on rocky SOTA summits where there is not much space, or the good footing needed to
          set up other types of antennas.

          Shortly after completing the portable loop I activated two SOTA summits hoping to get an indication of how well
         this home brew loop was working. The first was on March 6, the second March 10 of 2014. I worked 40 thru 15
         meters both days remaining on each band well past the last caller. I had 52 Qs on the 6th and 44 on the 10th, or 96
         total. Broken down: 10 on 40mtrs, 19 on 30mtrs, 35 on 20mtrs, 15 on 17mtrs, 17 on 15mtrs. DX was G4OBK and
         OH9XX worked on both days, G3VXJ, CT1BQH, EA2IF, HB9XH, VE7KBN, all on 15mtrs except for G4OBK
         who was worked on 17 both days. All QRP QSOs, using my FT-817! That I made any 40 meter QSOs at all with this
         small of a loop was especially encouraging!
       
         My experience with the Mag Loop has been both educational, and enjoyable, admittedly because they have worked
         as well as they do.  The picture below is of one of the first loop tuners that I built and still use.

                                             
         A Vernier Drive was added to the main tuning capacitor for ease of tuning. Using a 43 inch dia. loop it would cover
         15 thru 30 meters. A switch was added to add enough fixed capacitance across the tuning capacitor to bring the total
         up to 162pf to add 40 mtrs. To operate on 10 mtrs the size of the loop would have to be reduced because of the
         minimum and stray capacitance of the tuner. Using aluminum tubing for the loop has a weight advantage over copper
         and is freestanding on a picnic table in light wind. About 50 pf is needed for loading, and a dual gang Cap is not
         necessary.  

                        

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