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Signal should be heard.
  
By the magic of demodulation the signal is now at audio
frequency.
  
The high-frequency wave has done its work of carryzng
the message and has been dismissed. Only the original
modulating frequency (voice or music) should remain.
  
A detailed discussion of demodulation is beyond the scope
of this paper but may be found in any good textbook.
Successful signal tracing is first of all a matter of the
understanding. The hand that moves the probe must be
guided by an intelligence that knows the function of each
part and its relation to every other part.
  
The demodulator or detector Is simply
a rectifying device that passes the
postive half of the high-frequency
wave but gives poor conduction on the
negative half. By means of filters,
these positive pulses are joined to form
the original modulating wave.
  
For purposes of signal tracing, adequate
knowledge of the detector circuit
can be obtained from a study of
the functional diagram given in Fig. 7.
Fig. 7. Functional diagram of a typical detector circuit.
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