Automatically controlled equalizer utilizing a field effect transistor

Claim 1

A rapidly variable equalizer circuit with a wide control range for automatically compensating changes in the frequency dependent loss of transmission lines resulting from changes in the temperature and environmental conditions, comprising, in combination: a. a passive four-terminal control network including: 1. a pair of input means for connecting said passive fourterminal network to a transmission line carrying an assigned frequency signal, 2. a series resistance connected to the input side of said control network, 3. a shunt resistor connected within said control network, 4. a second four-terminal reflection free network connected in series with said shunt resistor and within said control network, said shunt resistor and said second network together constituting a shunt resistance within said control network having an impedance equal to the sum of that of said shuntresistor and of the input impedance of said second fourterminal network; and 5. a field effect transistor having its source-drain path connected to terminate said second four-terminal network and serving as an adjustable ohmic resistance; and b. means at the output of said control network for adjusting the source-drain resistance of said field effect transistor in response to the value of the assigned frequency signal appearing at said output and including: 1. peak rectifier means having an actuation threshold and producing a DC control voltage, 2. adjustable means for controlling the value of said actuation threshold, and 3. means for applying said DC control voltage to the gate of said field effect transistor.