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

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

9. Details - Capacitors
Trombone

10. Details - Capacitors
Butterfly

11. Details - Capacitor Trombone, Split-Stator, and Butterfly 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

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

21. Questions