Small Transmitting Loop Antenna Calculator

Small transmitting loop antennas, commonly called "magnetic loops" or "mag loops," can give surprisingly good performance when they are carefully designed and constructed. Although this online calculator is intended to assist with designing and building homemade, ham radio loop antennas for use in the HF bands, magnetic antennas have been constructed that function in the VHF or even the UHF frequencies. The most common material for home building small ham radio loop antennas is common copper plumbing pipe.This calculator enables you to test the design of an octagonal loop antenna and to answer "what if" questions until you arrive at a design that meets your needs without a lot of experience in electronics.

Length of Conductor (antenna "circumference")
Diameter of Conductor
(For efficiency, should be > 3/8" or 1 cm)
Transmitter Power (optional)

Units of Measurement


Antenna efficiency:
Antenna bandwidth:
Tuning capacitance:

Capacitor voltage:
Resonant circulating current:
Radiation resistance:
Loss resistance:
Inductive Reactance:
Quality factor (Q):
Distributed capacity:

Antenna perimeter "circumference:"
Loop antenna Side length:
Antenna diameter:


Input Values:
Length of conductor:
Diameter of conductor:
Transmitter power:

The ARRL Antenna Book: The Ultimate Reference for Amateur Radio Antennas, Transmission Lines And Propagation

The ARRL Handbook for Radio Communications

Related Pages:
Design your own tuning capacitor for use with this antenna with the
Capacitance Calculator (Capacitor Design)

To use the calculator:
Choose the units of measurement, English or metric.

2. Enter the length of the antenna conductor, which is the distance around the loop. The length should be between 0.1 and 0.25 wavelength at the desired operating frequency.

Enter the diameter of the conductor. 
Note: Small transmitting loops have very low radiation resistance and very high circulating current, so the diameter of the conductor must be large to assure reasonable efficiency—around 1" or 2.5 cm for the HF bands. #12 wire (for example) will not work.

Enter the frequency of operation.

Enter the transmitter power. This is optional, but it must be entered if you want to calculate the voltage at the capacitor and the circulating current.

Press Calculate.