MAGNETIC LOOP

 

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   When I was in France, I lived in an apartment in the center of my city. My needs was a small antenna with good reception for the allowed space, that’s why I decided to build a Magnetic Loop. The antenna build could be very simple or more complex, depends of what you want to do : chosen frequencies, motorized capacitor, automatic tuning, commercial or homemade capacitor...

   In my case I opted for these caracteristics :

- 20 to 10m

  1. -Homemade air capacitor : I wanted to know how to make one.

  2. -Motorized capacitor with remote.


   Here are my best links for this antenna :

  1. -F3DD : All the steps are very well explained. It’s a french website.

  2. -CALCULATOR : Simple and clear online calculator for octogonal loop.

  3. -PY1AHD : AlexLoop, great job with some details on his loops.

  4. -PA3GGI : Wonderful Loop antenna with automatic tuning system.

  5. -N4SPP : Great page, many informations.


   You will find my comments and observations on the photo gallery.

INTRODUCTION

   The best way I found to tune the antenna is to use an MFJ259 with a 2 way switcher. First way to the transceiver and second to the antenna analyser. Tune the variable capacitor for a peak in reception on the transceiver, then switch to the antenna analyser for fine tuning.


   In reception against the buddipole, the loop was better in all conditions : urban or in field. For transmitting the gap is smaller, sometimes the buddipole wins sometimes it’s the opposite. I recorded a short video during my portable operation in France. You can heard the difference between a Buddipole and the magnetic loop.

TIPS AND TESTS

   This magnetic loop was a beautiful experience, which have permit to learn many things. It’s a great antenna for who is in urban situation with no many space allowed for this activity.

   The only dark point is the narrow bandwidth, around 20 to 80khz, depends to the bands. If I have to build another one (20-10m), I will improve some points :

  1. -Replace the air capacitor by a vaccum 5-100pf for at least 5kv. You can also use more capacity in order to use the antenna on others bands but your efficient will be very bad. The main factor for efficient is the loop diameter.

  2. -Find an electronic system for a real time automatic tuning.

  3. -Increase the tube diameter for improve the bandwidth.

CONCLUSION