A Simplified Method for Deriving Additional Spurious Response Information from Receiver Measurements

Abstract

The majority of the work on the measurement of spurious responses in receivers done up to now is based upon the measurement of the sensitivity of all spurious responses for each of a few (usually three) tuned frequencies within the tuning range of any one receiver or major radio frequency head. These responses have been identified as the products of the nonlinear mixing of the incoming and local oscillator signals, most often in the mixer. Very little has been said about how the sensitivity of these responses varies with tuned frequency except to assume that the worst response of a kind found applies for all such responses. This paper examines the mechanisms involved in their generation and defines the factors upon which their sensitivity depends. These are basically the coefficients of the nonlinear equation representing the characteristics of the mixer and the radio frequency selectivity preceding the mixer. By use of a selective testing method, these two factors can be separated. Once this has been done, the total spurious response characteristic of the receiver is implied and the whole tuned frequency-spurious response frequency matrix can be filled in with reasonable accuracy. This selective testing method is certainly more productive of information per unit test than the method which is the present standard for such tests. However, the proposed method has not been adequately tested as yet, and it is hoped that this paper will result in such tests.