Barrett 2018 Mobile magnetic loop HF antenna

The Barrett 2018 Mobile magnetic loop HF antenna is an autotuning antenna consisting of a hinged arm (the loop) mounted to an aluminum vehicle roof rack. The magnetic loop, when correctly tuned, is capable of achieving a 10-14 dB gain in efficiency over a mobile whip.

The antenna is fundamentally a parallel tuned LC resonant circuit with the radio attached to a feed-point in the inductive arm from the circuit. The capacitive component is variable and driven by a stepper motor under microprocessor control. Tuning is performed by identifying peak antenna current followed by a VSWR minimisation algorithm.

Together with a high Q, the antenna has low angle nulls towards the sides, which helps to reduce noise from adjacent sources of interference. As the dominant radiation pattern is directed towards the ionosphere and is fundamentally near vertical incidence sky wave, it overcomes the dead zones, a common limitation of a typical mobile whip antenna. Due to its high efficiency, the antenna is effective over short distances.

RF and DC power is supplied through the transceiver working from the vehicle battery.