GB647064A - Improvements relating to apparatus for plotting the directional characteristics of wave propagating and/or receiving devices, such as radio aerials - Google Patents

Abstract

647,064. Measuring sound and like vibrations. MILLER, C. W., MILLING, M. C. CROWLEY-, and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Oct. 1, 1947, No. 26531. [Class 118 (ii)] [Also in Groups XXXIX, XL (b) and XL (c)] In apparatus for determining the directional characteristics of wave propagating and/or receiving devices, the device under test is caused to transmit waves to or receive waves from a co-operating device and is moved angularly with respect to said device, whilst apparatus acting on the transmitting or receiving device is controlled to give a constant amplitude output from the receiving device whereby the settings of this apparatus provides a measure of the relative efficiency of the device under test at different angular positions. The invention is described as applied to the determination of the polar diagrams of radio aerials, but is stated to be applicable to sound emitters. Fig. 1 shows apparatus for testing a transmitting aerial, the aerial being mounted for rotation about a vertical axis and energized from an oscillator through attenuators including a calibrating attenuator controlled by a servomotor system. The radiated waves are received by a stationary aerial situated some distance away, the output of which, after amplification and rectification, is compared with a D.C. reference voltage in a balancer circuit. The balancer output controls the attenuator servomotor system and any inequality between the received and reference voltages results in a variation of the transmitting aerial power until balance is achieved. In effect, as the aerial under test rotates, the received voltage is maintained constant by variation of the attenuator, the settings of which thereby indicate the aerial directivity. A drum recorder controlled in accordance with the attenuator settings and the aerial angular position produces a plot of the aerial field strength at different angles. Fig. 2 (not shown) illustrates apparatus for testing receiving aerials. The Specification discusses a number of auxiliary features including: the use of cathode-ray tube recorders; the elimination of noise from the receiving channel; methods of deriving the reference voltage from the oscillator to eliminate errors due to variation of oscillator power during a test; and a method of controlling the speed of aerial rotation in accordance with the rate of change of attenuator setting in order to plot the directivity curves slowly where the field strength changes rapidly and vice versa.