GB710378A - Improvements relating to measurement of r.f. power - Google Patents

Abstract

710,378. R.F. power, voltage, measurement. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 27, 1952, [Dec. 10, 1951.] No. 28886/51. Class 37. In apparatus for measuring radio frequency power, a source 1 of power to be measured is coupled through a calibrated variable attenuator 2 to a wave guide section' 9 within which a fluorescent lamp 3 alternately switched on and off by a modulated voltage source 5 is positioned between the power source and a crystal mixer 4 connected to a D.C. measuring circuit 7. Variable attenuators 8 are provided in the waveguide between the lamp and the mixer, and between the mixer and a local oscillator 6. The lamp is rotatable in a horizontal plane parallel to the magnetic vector about a vertical axis at the middle of the waveguide to match it to the waveguide impedance, and when inoperative allows R.F. energy to pass from the power source to the mixer while when operative its positive column strongly absorbs such R.F. energy and radiates R.F. noise energy into the waveguide. Thus the R.F. energy from the source is continuously chopped by the lamp energization and in the alternate intervals the mixer receives pulses of R.F. noise energy, so that if the relative amplitudes of the signals are adjusted by attenuators 2 and 8 until the indication of the mixer measuring circuit is the same when the lamp chopping circuit is disabled as it is when the circuit is operative, it is shown that the lamp output power is twice that of the unknown source. Alternatively the lamp output power is adjusted for minimum fluctuation of the mixer signal at the chopping frequency, when the lamp power will equal the unknown source power. The difference in power output between the known lamp output and that of the power source may be retroactively fed back to stabilize the latter.