Standing-wave indicator for 3¿22 Mc/s

The usual methods of measuring standing waves on feeder lines involve the use of: (1) Thermocouple instruments, which have poor overload characteristics and high mortality, and whose square-law scales seriously limit the range of standing-wave ratio measurement. (2) Rectifier and microammeter, the latter an expensive and delicate instrument. In the new instrument the radio-frequency current induced in the shielded loop coupled to the feeder lines, is rectified by a midget diode. An adjustable portion of the d.c. voltage across its load resistor is applied through 100 ft of cable to a d.c. amplifier, which operates a milliammeter (0¿10 mA) of robust and tropical type, or an external meter. The instrument is self-contained and comprises loop and diode unit¿stowed in lid of case for transit¿adjustable for all usual transmission- line spacings, and a metal case containing the d.c. amplifier, meter and battery power supplies. Thus this instrument avoids the defects of (1) and (2) above, as overloads will not cause damage, and the sensitivity control permits adjustment over a wide range of test powers.