The practical value of signal tracing as a means of rapidly locating trouble
in radio circuits is too well known to require any special pleading. Even
when used by an inexperienced radio student, this method gives his tentative
efforts a quality directness and continuity In the hands of an expert, the
technique identifies and isolates trouble with incredible speed.
In radio servicing, no man can attempt to clear trouble intelligently unless he knows the function of each part ind it relation to every other part. Aside from its practical utility, signal tracing has great educational value. Even on paper, without instruments, a student may be taught to trace the signal from point to point, to describe its character, and to account for any deviation from normal operation.
A most helpful exercise, both for practical work and for an underanding of principles, is to follw the signal along its entire trip through the receiver. A detailed and lettered diagram may be used to indicate the points at witch the signal will be examined. Other points will be tested to make sure that the signal has not wandered off onto forbidden paths.
Fig. 4 shows a conventional superheterodyne receiver with one untuned r.f. stage, diode detector, a.v.c., and pentoded output. If the student will master this fundamental circuit, if he will learn "the funciton of each part and its relation to every other part," he will find that hew knows something about radio.
A standard radio receiver can be converted easily into a simple dynamic tester. Such an instrument was covered in an article entitled "Clearing That Intermittent," which appeared in the September, 1944, issue of Radio News. It traces the signal audibly from antenna post to voice coil. The use of an analyzer of this type (or any professionally manufactured unit) gives rise to the detailed analysis that follows.
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