Automatic impedance matching with potential monitoring means

DETAILED DESCRIPTION In accordance with one aspect of the present invention, a method of impedance matching a transmitter to a transmission medium of a communication system during normal operation of the system comprises feeding signals from the transmitter to the transmission medium through variable impedance means; monitoring the potential upstream and downstream of the variable impedance means; generating a control signal related to the monitored potentials; and adjusting the impedance of the variable impedance means in accordance with the control signal until the monitored potentials satisfy matching conditions in which the transmitter is impedance matched to the transmission medium.
In accordance with a second aspect of the present invention, apparatus for matching a transmitter to a transmission medium of a communication system during normal operation of the system comprises variable impedance means connected in use between the transmitter and the transmission medium; monitoring means for monitoring the potential upstream and downstream of the variable impedance means; and a control signal generator for generating a control signal related to the monitored potentials, the control signal being fed to the variable impedance means so as to vary the impedance of the variable impedance means until the monitored potentials satisfy matching conditions in which the transmitter is impedance matched to the transmission medium.
The invention provides real time impedance matching in which the impedance matching process is carried out during normal operation of the system without the need to use special test equipment.
Furthermore, by monitoring the potential upstream and downstream of the variable impedance means, much simpler circuitry can be used than in the case of U.
S.
Pat.
No.
4,004,102.
Preferably, the matching conditions are satisfied when the potential downstream of the variable impedance means is substantially one half the potential upstream of the impedance matching means.
Typically, in this case, the monitoring means includes a divide by two circuit to which the potential upstream of the variable impedance means is fed and a comparator to which the output of the divide by two circuit and a signal corresponding to the potential downstream of the variable impedance means are fed, the output of the comparator constituting the control signal