Antenna analyzer

[technoguy]

An antenna analyzer (or noise bridge, or RX bridge) is a bridge where two legs are frequency-dependent complex-valued impedances. When the two impedances are the same the bridge will be balanced. Using this circuit it is possible to either measure the impedance of the antenna connected between ANT and GND, or it is possible to adjust an antenna until it has the same impedance as the network on the left hand side. The bridge can be driven either with white noise or a simple carrier (connected to drive). In the case of white noise the amplitude of the exciting signal can be very low and a radio receiver used as the detector. In the case where a simple carrier is used then depending on the level either a diode detector or a receiver can be used. In both cases a null will indicate when the bridge is balanced.