GB678836A - Improvements in or relating to high frequency electrical power measuring apparatus - Google Patents

Abstract

678,836. High-frequency power measurements; bridge circuits. GENERAL ELECTRIC CO., Ltd., and FLINT, F. C. April 19, 1951 [April 19, 1950], No. 9619/50. Class 37. A high-frequency power measuring apparatus comprises a resistance bridge 1 having in one arm a bolometer or other temperature-sensitive resistance 3, which is also connected in the highfrequency circuit the power in which is to be measured. The diagonal 5, 11 is supplied with D.C. from a full-wave rectifier 10 through a milliammeter 8 and resistances 6, 7. Across the same diagonal is a resistance 13 in series with a D.C. milliammeter 14 and a part of a potentiometer 15, which is connected across a half-wave metal rectifier 17. The bridge 1 is supplied between the corners 21 with lowfrequency A.C. from a valve oscillator 20,. balance being detected by an amplifier 23 and D.C. microammeter 24 connected across the diagonal 5, 11. Without applying any highfrequency power to the bolometer 3 the bridge is balanced by adjustment of the output of the oscillator 20, the D.C. through the milliammeter 8 being adjusted to a predetermined value. The bridge balances when the power dissipated in the bolometer 3 by both the A.C. from the oscillator 20 and the D.C. from the rectifier 10 raises its temperature to the point where its resistance is equal to that of the resistor 4, the arms 2 being equal. The highfrequency power to be measured is then applied to the bolometer, raising its resistance and unbalancing the bridge. The bridge is again balanced by reducing the D.C. flowing in the bridge by adjusting the potentiometer 15 so as to increase the D.C. shunted through the resistance 13. The D.C. through the bridge is reduced by this amount and the resistance of the bolometer 3 is lowered until the bridge is again in balance. The reading of the milliammeter 14 is a measure of the high-frequency power and may be calibrated to read power directly. Alternatively the amplifier 23 may actuate a servo-mechanism to drive the variable tap of the potentiometer 15 until the bridge is balanced. In a further form of self-balancing bridge the resistor 13 is replaced by a valve, the potential on the control grid of which is controlled by the output of the amplifier 23. The valve then passes a current dependent on the degree of unbalance of the bridge. Reference has been directed by the Comptroller to Specification 592,119.