Locating Interference Sources

Radio Record, Volume IV, Issue 34, 6 March 1931, Page 15

Locating Interference Sources

NEw ZHALAND listeners whose reeeption is marred by interference will be interested to learn that an instrument which takes the guess out of trouble-hunting and accurately measures the quantity of electrical interference in micro-volts per meter has been developed by the General Blectrie Company of New York. The new instrument is called a radio noise meter, and is not to be-confused with meters made to measure noises audible’to the humanear. This meter

records the quantity of noise, generally described as electrical interference, made audible only by radio receivers. The meter locates the source of the noise and measures its intensity: The need for a measuring instrument has been felt for some time, and many radio organisations have been hampered in their efforts to improve radio receiving conditions by the lack of a standard testing instrument and a standard of measurement. The noise

( the test results of different investigators; it gives manufacturers of: electrical apparatus a means for measuring the amount of radio noise created by the apparatus. In addition, an inyaluable method of obtaining data upon which fair and reasonable rules and ordinances may be based is: provided. "Pe Many municipalities, anxious to pro‘tect radio listeners from excessive electrical interference, have passed ordin-. ances limiting "permissible" interfer‘ence. The trouble, heretofore, has been to define "permissible." The radio noise meter consists of two parts, a receiver unit to detect and indicate radio noise, and a calibrating unit to measure the intensity of the noise in micro-volts. per meter, which is the customary unit of measurement of ‘radio signals. ot se The receiver is enclosed in an aluminium box, and weighs thirty pounds. Six valves are used. The pick-up is obtained with a rod antenna, two meters long. Using the meter a radio noise corresponding, to a field intensity of three micro-volts per meter may -be measured. With the headphones it is possible to measure still lower noise levels. A search coil may be used to investigate noises around’ motor brushes, transformer ground leads, ete. The calibrating unit is also’ enclosed in an aluminium box which is fastened to the side of the receiver, and it is so’ designed that the radio noise may be measured with any antenna that may be used with the receiver. The output of the calibrating unit may be varied from zero to 10,000 micro-volts per meter. , ny A feature of the instrument is the standard noise created, by means of which it becomes possible to measure the intensity of the interfering noise, Operation of the instrument consists im adjusting the intensity dial until the standard noise reads the same on the meter as the radio noise. The intensity in micro-volts per meter is then read from a curve, Switching from stand ard to radio noise is accomplished by, depressing and releasing a key switch. The standard noise is obtained by al ternately charging a network of small j -condensers from a dry battery and dia charging into the antenna in such & way as to produce a noise that closely imitates the usual transmission line) noise. — 8 The portability of the instrumené makes it readily applicable to tests in the field, in the home, or wherevet the radio noise may occur. It is especially useful to measure radio noise on transmission lines, house-wiring, around distribution points, or electrical apparatus of any description.