Field Strength Meter Research Articles

A Magnetic Field Strength Meter Employing the Hall Effect in Germanium

The instrument to be described measures magnetic field strengths as determined from the Hall effect in germanium. The essential parts of this instrument include a small germanium probe, and a panel type microammeter calibrated directly in gauss. Its accuracy is ±2 percent at fields between 100 and 8000 gauss. At higher fields the readings are too low, the error amounting to 9 percent at 20,000 gauss. The chief advantages of this instrument are: (a) small size and portability, (b) continuous reading rather than ballistic as in ordinary field strength meters, and (c) a small non-magnetic probe with which one can search in very narrow gaps.

Synchronization of Oscillators

A theory is presented which predicts the behavior of any self-limiting oscillator in the presence of an injected sinusoidal voltage or current of small but constant magnitude. The internal mechanism responsible for synchronization is not needed, and the theory is thus applicable to any source of alternating current. Experimental verification of the theory is presented for the case of a low-power Hartley oscillator operating at 11.5 Mc. The theory is extended to include the mutual synchronization of two oscillators of arbitrary properties, and applied to a number of examples to indicate briefly the properties of a synchronized oscillator when used as (a) a linear voltmeter for small voltages, (b) a field-intensity meter, (c) a linear a.m. demodulator for small signals, (d) an f.m. demodulator, and (e) a synchronous amplifier-limiter. The use of a synchronized oscillator is of particular interest because microwave generators can be used in addition to the more conventional triode oscillators.

Synchronization of oscillators

A theory is presented which predicts the behavior of any self-limiting oscillator in the presence of an injected sinusoidal voltage or current of small but constant magnitude. The internal mechanism responsible for synchronization is not needed, and the theory is thus applicable to any source of alternating current. Experimental verification of the theory is presented for the case of a low-power Hartley oscillator operating at 11.5 Mc. The theory is extended to include the mutual synchronization of two oscillators of arbitrary properties, and applied to a number of examples to indicate briefly the properties of a synchronized oscillator when used as (a) a linear voltmeter for small voltages, (b) a field-intensity meter, (c) a linear a.m. demodulator for small signals, (d) an f.m. demodulator, and (e) a synchronous amplifier-limiter. The use of a synchronized oscillator is of particular interest because microwave generators can be used in addition to the more conventional triode oscillators.

A field-strength meter and standard radiator for centimetre wavelengths

The paper describes the development of a field-strength meter and standard radiator for operation at a wavelength of about 9 cm. Details are given of a modified form of Wheatstone Bridge which can be calibrated to give direct readings of the power absorbed in a bolometer. The field-strength meter takes the form of an electromagnetic-horn receiver in which the received power is measured by means of a bolometer. It is shown how the gain of such an aerial may be determined experimentally, and how, knowing this gain, the field-strength existing at the aperture of the horn may be found. The range of power measurable by the bolometer used limits the field-strength range of the equipment to 0.1–50 V/m. The standard radiator consists of the same type of horn as the field-strength meter but with small modifications.A description is given of the application of the two instruments to the determination of the power radiated by a transmitter, and to the estimation of the over-all sensitivity of a receiver.

A Compact Radio Field Strength Meter

This paper describes a compact portable field strength meter for frequencies in the broadcast band. The range of the instrument is from one volt per meter to one millivolt per meter. The theory of the resonant circuit is elaborated, and on the basis of the theory a novel method for calibrating the detector circuit is developed. A minimum of calibration is required for the instrument as a whole. The voltmeter may be calibrated on audio-frequency alternating current; and any loop used may be calibrated by the instrument itself in the field.