TABLE OF CONTENTS GUY DOUGLAS
Hewlett-Packard Ltd.
The white-noise-loading technique is normally used as the final arbiter in determining analog microwave radio performance. White-noise measurements provide a quantitative measure of that performance in order to make a decision to go or not. No alignment or diagnostic information is readily available using this technique. Meanwhile, swept frequency measurement techniques are normally used to align the various subsections of a radio for example, the modulator or IF equalizers in terms of their linearity, group delay, and IF amplitude characteristics or to diagnose faults on a previously working system. The objective of such alignment adjustments is to minimize distortion, but the relationship between deviations in these characteristics and the baseband distortions that result under traffic loading conditions is not obvious. For this reason, white-noise loading, which simulates normal traffic, must be used to confirm the validity of the alignment obtained using swept measurements.
The aim of this chapter is to show that (1) some diagnostic information can be obtained from white-noise measurements, particularly with the availability of automatically controllable instrumentation and low cost computing power, and that (2) some qualitative information can be realized from swept-frequency measurements using rule-of-thumb techniques. The benefits of this are, from (1), that trouble-shooting activity can converge more quickly to the source of the problem and, from (2), that the source of the distortion can be identified to the shape of a particular characteristic and that guidelines for realignment can be developed.
