Lumped component standing wave ratio indicators for radio frequency transmission lines

Claim 1

Apparatus for measuring the standing wave ratio on a radio frequency transmission line, including a toroidal current transformer arranged around the transmission line and having a toroidally wound secondary wire thereon; an electrostatic screen positioned between the line and the current transformer; a first voltage dividing chain composed of first and second serially connected impedances connected across the secondary wire of the current transformer; a second voltage dividing chain composed of third and fourth serially connected impedances connected between the transmission line and ground; a conductive connection for interconnecting the junctions between the first and second impedances and the third and fourth impedances such that voltages proportional to the forward and reflected voltages on the transmission line are obtained at either end of the first voltage dividing chain; a pair of identical circuit arms each comprising a resistor and a diode connected in series across a capacitor to form a parallel circuit therewith, and a further diode connected in series with said parallel circuit, each one of said pair of identical circuit arms being connected between respective ends of the said first voltage dividing chain and ground for deriving further voltages from the first voltages which are dependent upon the logarithms of the derived forward and reflected voltages; and a voltage comparator means for automatically comparing said further voltages and producing a measurement of the standing wave ratio on the transmission line in accordance therewith.