Voltage Quantities Research Articles

A double-input laboratory oscilloscope

THE ELECTRICAL engineering student engaged in a study of a-c theory is helped immensely in gaining a basic understanding of the interrelationships between the voltage and current quantities in a circuit when he is able to observe and study at least two of the quantities simultaneously. However, commercial apparatus which makes this possible, the oscillograph, the cathode-ray tube oscilloscope with “electronic-switches,” and double-beam cathode-ray tube oscilloscopes, have been little used by the student himself because the problems of interconnections, time-base adjustments, synchronizing, calibration adjustments, and the like are beyond the abilities of the average student commencing his study of a-c circuits.

Radio measurements in the decimetre and centimetre wavebands

The paper deals with the technique of radio measurements evolved as a necessary aid to the development of decimetre- and centimetre-wave valves, circuits and equipment, and surveys some of the methods applicable in this wide field. It commences with a review of the circuit theory of coaxial and wave-guide transmission lines, followed by a short section on high-frequency oscillators.Succeeding sections deal with the measurement of the fundamental quantities of frequency, power, impedance and voltage. Heterodyne methods of frequency measurement, and coaxial and resonant cavity wavemeters, are described. The design of bolometer and calorimeter circuits is discussed for powers between 1 microwatt and several hundred watts. Measurements of reflection coefficient and Q-factors are included in the section on impedance.The concluding sections deal with derived measurements: receiver sensitivity, aerials and field strength. A standard of receiver sensitivity is established, based on thermal noise voltage, and the design of suitable signal generators and sensitivity measuring equipment is discussed. The section on aerials comprises measurements of polar diagram, gain and impedance. Finally, equipment for the absolute measurement of field strength at centimetre wavelengths is outlined.