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Exploring Mag-Loop Antennas: Basics, Benefits, and DIY Possibilities

Discover the fundamentals of mag-loop antennas, their advantages in size and noise reduction, and learn how to create your own. Get insights on tuning, best practices, and future project ideas through detailed results and tuning experiences. Find essential web resources for further exploration.

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Exploring Mag-Loop Antennas: Basics, Benefits, and DIY Possibilities

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  1. What Are They, Why Use Them, and Can I Make My Own?? Mag-Loop Antennas

  2. What We Hope to Accomplish • Basics of a Mag-Loop Antenna – Keep It Simple • Absolute minimum of math • My “first” Mag-Loop – example • Resources

  3. What is a Mag-Loop • A loop antenna <1/4 wavelength • A tuned circuit with an inductor and variable capacitor

  4. Why Use a Mag-Loop? • Small size – • Allows stealth – Covenants, Homeowner Ass. • Ease of handling • Less sensitivity to ground – Doesn't need great height • Low noise pickup, especially on lower bands

  5. Some Details

  6. Details • Lots of current – Use minimum of connections • If > ¼ wavelength circumferance – Self oscillations - unstable

  7. Details – Loop Coupling Easiest method of coupling - Some variations reduce noise pickup

  8. Details - Capacitors • Vacuum Split Stator High Voltage & High Current unless QRP

  9. Details - Capacitors • Trombone

  10. Details - Capacitors Butterfly

  11. Details - Capacitor • Trombone, Split-Stator, and Butterfly • Half the capacitance • Twice the voltage rating • Less series resistance • Butterfly • ¼ turn min to max

  12. Best Practices • Use vertically – FAR less sensitivity to ground • Elevation above ground - • Slight effects on coupling • Some effect on take-off angle • Clearance from other metal objects • Null out interferences if good contact is made • Gear reduced motor drive for tuning

  13. My Mag-Loop Antenna

  14. My Mag-Loop Antenna - Results • The antenna was compared to a trap-dipole 28' elevation at the center, approx. 8' at the ends. • Legs on ground- bottom of loop 2' above ground • Good receive, 2 S-units below trap dipole • Perfect match at tuned frequencies (20m) – 1:1 SWR • No contacts made • Legs on chairs – bottom of loop 3.5' above ground • Receive still 2 S-units below trap dipole • Match increased to 1.5:1 SWR. Readjust coupling loop?? • Contacts in plane of the loop were also 2 s-units from trap dipole (contacts were in Oklahoma and Texas)

  15. My Mag-Loop Antenna - Results Tuning: • Extremely touchy – absolutely requires a gear reduction and motor drive! • ~50kHz bandwidth at 2:1SWR for a given tuning in the 20m band. • Need to reduce number of capacitor plates to raise frequency and reduce frequency swing • Switch in door-knob caps for lower band(s)

  16. Future Mag-Loop Projects 80/160m Loop

  17. Future Mag-Loop Projects Convoluted Mag-Loop

  18. Future Mag-Loop Projects

  19. Web Resources http://www.brisdance.com/vk4amz/files/Download/UnderMagLoop.pdf http://www.aa5tb.com/loop.html http://www.aa5tb.com/aa5tb_loop_v1.22a.xls http://www.66pacific.com/calculators/small_tx_loop_calc.aspx http://viennawireless.net/wp/wp-content/uploads/2017/01/Magnetic-Loop-Antennas-W4RAX.pdf http://www.on4ceq.net/ant_en.htm

  20. Material Covered • Mag-Loop Antennas – What and Why • Some Technical Details • Use • Some Possible Variations • Resources

  21. Questions

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