Aircraft radio interference measurements

IT IS essential to know the wave shapes and statistical distribution of impulsive interference transients for working out adequate interference-reduction methods. Interference pulses such as are produced by corona and sparking phenomena in electric equipment present a serious problem in measurements. Conventional noise meters convert any kind of pulse to the same fundamental shock excitation wave shape determined by the characteristics of the initial circuits and thus the original character of pulses is masked. The noise meter is useful in assisting in the routine elimination of noise from various electric devices, for it informs the investigator of the progress made and it indicates when the noise is of such a character that it will no longer cause appreciable disturbance in a typical receiver. However, for interference studies covering a wide frequency range, evaluation of the noise level requires a vast number of laborious measurements with different instruments for each range of frequency and type of communications. When evaluating atmospherics or other interference that changes character with time, noise meter measurements cannot be made quickly over a wide frequency range. Thus for a fundamental study of the nature of interference, the oscillograph provides more useful information. A highspeed oscillograph is of value even in routine suppression tests, since it can show the effect of each suppressive device on the undesirable transient graphically.