Silent Tuning: Matching a transmitter to an antenna without emitting a signal

Abstract

This work describes a practical alternative for antenna matching by leveraging the relatively recent availability of small, portable vector network analyzers. Unlike traditional antenna analyzers which only measure SWR, these instruments provide an accurate measurement of complex impedance and easily cover the high frequency (HF) range. The antenna described here combines a network analyzer sweep of the antenna impedance with a pre-measured mathematical model of the tuner itself in an optimization process to predicatively tune the antenna. Except for the signal needed by the network analyzer (which is typically less than 1 mW) the tuning process is accomplished with no emission from the antenna before actually communicating (which might, itself, be a frequency hopping scheme). A working system is described for Near Vertical Incident Skywave (NVIS) communications which achieves an standing wave ratio (SWR) of less than 1.2:1 over the frequency range of 1.8 to 8 MHz.