Maximizing magnetic antenna performance is an exercise in mathematics. A full-wave wire loop antenna is calculated by using the formula 1005 ÷ freq (mHz) = Length (feet). A magnetic loop antenna is defined as a loop that is 10% or less in size of a full-wave loop antenna. MagLoops with maximum efficiency on 80 meters would be calculated by 1005/3.5MHz = approximately 287′ X 10% to achieve magnetic loop lengths, which is right at about 28.7’. For example, on 40 meters the calculation would be 1005/7Mhz = about 143.5′ X 10% to achieve loop lengths, which is right at about 14.4’. As a result, maximum averaged efficiencies are achieved from 40 through 80 meters. This is because the average of these two lengths for 40 & 80 meters, 21.55’ (28.7’ + 14.4’ / 2) are used. Proof is to follow:

Design Notes

In the final design, a double loop adds inductance that allows the loop to be tuned to lower frequencies with the same capacitor. The area within the loop is increased when the 11’9” booster cable is installed to the default 9’4” 10-40M outer loop. As a result, the total circumference of the 40-80 Meter Alpha Loop is the just over 21.55’; and has a 21% increased area within the loop. This is why maximum efficiency is realized for both 40 and 80 meters on this antenna: 100W 6M VHF UHF Loop 10-40M & 20W 80M HF Magnetic MagLoop by Alpha Antenna.

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CALCULATING MAXIMUM AVERAGED EFFICIENCY

Averaged Magnetic Outer Loop Length for 40 to 80 Meters

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BASE CALCULATIONS

Full Loop Calculation: 1005 ÷ freq (mHz) = Length (feet) of element

Magnetic Loop Calculation (Maximum Outer Loop): Length (feet) X 10%

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CALCULATED INPUTS

80M Full Loop Length: 1005/3.5MHz = approx 287′

80M Maximum Magnetic Loop Length: 287′ X 10% = 28.7’

40M Full Loop Length: 1005/7Mhz = approx 143.5′

40M Maximum Magnetic Loop Length: 143.5′ X 10% = 14.4’

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MAXIMUM AVERAGED 40/80M MAGLOOP CALCULATION

(28.7’ + 14.4’) / 2 = 21.55’ or 21′ 6 1/2″

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CONCLUSION

As a result, the averaged outer loop length to maximize efficiency on 40-80M

21’ 6 1/2”

Actual 40-80M Outer Loop Element Length of the Alpha MagLoop Antenna

21′ 9″

REFERENCES:

Full Wave Loop Calculator: CLICK HERE

Magnetic Loop Antenna Calculator: CLICK HERE

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