# Modified WA8LMF Magnetic Loop 20m Figures

I use Glenn's, KI6GD's, excellent "Magnetic Loop Calculator" (I have v1.4, 2009) to help in the design and experimentation with small loops. For 20m, here are the numbers (the program works with either Imperial or Metric units and various materials and shapes (copper, aluminum and shapes round, square and octagon) all which will affect the final product. Note: According to my ARRL Handbook, Belden RG-213 has a rated breakdown voltage of 3.7kV (RMS) and at the 50 watts operating power level the capacitor voltage is 3.3kV. That's cutting the safety margin close, so I wouldn't push the loop past 50 watts and most my operating is 25 watts and way less. But, just how good is any of that cheap, no-brand "Made in China" coax, eh?

Efficiency is around 53% for 20m which seems to work since I can work DX and they can work me! When used on 30m it's just over 26% according to the calculator and I've only been able to work Canada/U.S. stations, mostly. A larger loop would be a better choice for 30m to increase the efficiency.

Loop Circumference 3.03 m (10' loop circumference, circular shape)

Conductor Diameter 12.7 mm (1/2")

Frequency 14.097 MHz

Power 50.00 watts (for maximum capacitor voltage calculation)

Bandwidth 16.9 kHz

Capacitor Value 33.5 pF

Capacitor Voltage 3.3 kV

Conductor Wavelength 0.151 lamda

Efficiency 53.1 % (circular is the most efficient, followed by octagon at 50.4% , then square at 41.1%)

Inductance 2.995 µH

Inductive Reactance 265.4 ohms

Loop Area 0.7 m² (8.0 feet²)

Loop Diameter 1.0 m (3.2')

Loop Q Value 832.4 Qres (outrageously high Q value at resonance, thus a narrow bandwidth but less noise with the signal)

Radiation Resistance 0.085 ohms

Resistance Loss 0.075 ohms

73,

Robert

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