Antenna analyzer

A bridge is available which measures complex impedance while the transmitter is operating, practically a necessity when tuning multi-tower antenna systems.

In the case of white noise the amplitude of the exciting signal can be very low and a radio receiver used as the detector.

The operator then uses mathematical methods to calculate complex impedance, or reads it off a calibrated meter or a digital display.

Many of these instruments have the ability to automatically sweep the frequency over a wide range and then plot the antenna characteristics on a graphical display.

The SWR meter requires about 5–10 watts of outgoing signal from the radio to register the reflected power (if any), and then only indicates the relative degree of mismatch, not the reactive and resistive impedance seen at the end of the antenna's feedline.

An antenna analyzer measuring SWR and complex impedance of a dummy load. MFJ-269, MFJ Enterprises Inc.
A typical antenna bridge, the trimmer capacitor ( C ) is adjusted to make the bridge balance when the variable capacitor on the left is half meshed. Hence the bridge will be able to detect if an antenna is either a capacitive or inductive load.