Terminated End-Fed Moxon FM Loop Antenna
|By Bruce A.Conti - June 2018|
This variation of the Moxon FM Loop, sometimes also referred to as the Faulkner Loop, is a terminated end-fed Moxon antenna for bi-directional FM radio broadcast reception. It produces a broadband low-angle figure-8 reception pattern covering 87 to 108 MHz with deep side nulls. The antenna impedance is approximately 300 ohms across the FM broadcast band, making it an easy match with 300-ohm twin lead/ladder line balanced lead in. The loop antenna is inherently low noise.
The terminated end-fed Moxon FM Loop antenna is a square loop in the vertical plane measuring 30 x 30 inches, constructed of aluminum tubing or copper pipe. Vertical polarization improves reception of vertically polarized low power FM translators. The original unidirectional Moxon antenna design is center-fed, not terminated, and isn't broadband enough to adequately cover the FM broadcast band. The addition of a series 300-ohm termination resistor to the end-fed Moxon produces deeper side nulls, 23 to 27 dB typical. Side nulls up to 30 dB can be achieved at a specific frequency by varying the termination resistance.