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Mag-Loop Antennas

What Are They, Why Use Them, and Can I Make My Own??. Mag-Loop Antennas. What We Hope to Accomplish. Basics of a Mag-Loop Antenna – Keep It Simple Absolute minimum of math My “first” Mag-Loop – example Resources. What is a Mag-Loop. A loop antenna <1/4 wavelength

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Mag-Loop Antennas

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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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