The testing of communication-type radio receivers

Tests for determining the performance characteristics of superheterodyne receivers for use in the frequency range 30 kc/s to 30 Mc/s for the reception of double-sideband amplitude-modulated telephony signals, and c.w. and m.c.w. telegraphy signals, are described. The measuring equipment required for the tests is stated and its desirable performance characteristics are summarized. The more important performance characteristics of the receiver are determined by tests covering such features as sensitivity, signal/noise ratio, selectivity, modulation-frequency response (including the acoustic response of the loudspeaker, if fitted), non-linearity and distortion of the a.f. output. The sensitivity tests include the use of a noise generator for the determination of the noise factor. Unwanted responses due to (i) a single signal, and (ii) the intermodulation of two signals, are described, together with the methods of measurement. The limitation of the effective selectivity of a receiver as a result of the non-linearity of radio-frequency and intermediate-frequency stages is referred to and assessed by means of the cross-modulation and blocking characteristics. The measurement of the performance of the automatic-gain-control and automatic-frequency-control systems is discussed, also the measurement of the drift of the frequency-change oscillator(s). Measured characteristics for typical receivers are given in order to illustrate convenient methods for the presentation of the results, and the values to be expected in practice.