Patent GB-595207-A (GB)
Title: Apparatus for measuring standing waves on radio-frequency transmission lines
IPC: G01R29/10
Filed: 1945-03-30
Abstract: 595,207. Current and voltage measurements. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. March 30, 1945, No. 8136. Convention date, March 30, 1944. [Class 37] Apparatus for measuring standing waves on a radio frequency transmission line comprises common lumped directional means providing capacitive and inductive coupling between the line and indicating means to provide an indication of the magnitude of waves on the line. The common directional means is arranged so that its directivity may be reversed so as to measure waves travelling in opposite directions. Fig. 2 shows apparatus for measuring standing waves on a coaxial transmission line 15 comprising an inner conductor 1 and an outer coaxial conductor 5. A second coaxial transmission line 76 comprising an inner conductor 6 and an outer conductor 7 is coupled at right angles to the line 15 by means of a bearing 8 connecting the outer conductors 5, 7 and permitting rotation of the line 76. An assembly comprising an inductor L, shunt resistor RL, and series resistor RC is secured to the inner wall of the outer conductor 7 of the line 76. The resistors RL, RC may be of graphite, and the coupling inductor L may consist of a rigid flat strip of metal formed into a rectangular loop and connected between one terminal of the resistor RC and the inner conductor 6 of the line 76. The stray capacitance between the inner conductor 1 and the coupling inductor L is represented by a capacitor C. An indicator 4 is connected between the inner and outer conductors 6, 7 of the line 76 at the end remote from the line 15. The coupling between the coupling inductor L and the inner conductor 1 may be varied by rotating the line 76, and the magnitudes of the forward and backward travelling waves on the line 15 may be made separately by rotating the line 76 through 180 degrees. The resistor RL may be omitted for low frequency readings. For initial adjustment a generator having an internal impedance. equal to the surge impedance of the line is connected across the line 15 which may be terminated at the remote end by an adjustable short-circuiting plug. The line 76 is rotated until the output indication on the indicator 4 is independent of the position of the short-circuiting plug. In a modification, Fig. 3, the line 76 is not coaxial but comprises a cylindrical outer conductor 7 having a central partition 9 shielding the inner conductor 6 from the resistor RC. In another construction, Fig. 5, for very high frequencies the transmission line 76 has its inner conductor 6 connected at one end to the outer conductor 7 through the resistor RC, which matches tthe line, the other end of the line being terminated by the indicator 4. The coupling inductor L comprises a closed loop situated inside a cylindrical conductive shell 10 and is adjustably coupled to the inner conductors 1, 6 of the two transmission lines. Adjustment of this coupling is effected by rotation of the shell 10 and line 76. Forward travelling waves on the line 15 may be measured with the line 76 in the position shown, and backward travelling waves may be measured by rotation of the line 76 and inductor L through 180 degrees. In a modification the line 76 is terminated at each end by an indicator so that simultaneous measurements of forward and backward travelling waves may be made.