How to Build Advanced Short Wave Receivers - The Listeners Guide

CHAPTER TWO
MODULAR SUPERHET
In the previous chapter the superhet principle was described,
together with very complete details of the circuit operation
and construction of a practical receiver. A sort of modular
form of construction was used with the circuit being divided
up into four main sections (the mixer/oscillator, the I.F. amplifier/detector/A.G.C.,
the audio amplifier, and the B.F.O.).
This modular approach was purposely adopted for two reasons.
Firstly it happens to be a very convenient form of construc~
tion, and secondly it leads up to this chapter where a number
of different superhet building blocks will be described. The
idea here is that the constructor chooses the various building
blocks which best suit his or her needs, and then assembles
these to produce a complete receiver.
This approach is perfectly feasible because superhet receivers
tend to naturally break down into such building blocks.
Provided one does not stray from standardised parameters
(470kHZ I.F.s, usual stage input and output impedances,
output levels, etc.), no problems with incompatibility between
building blocks will arise. These building blocks have been
designed so that they will fit together properly, without any
problems of compatibility occuring. Such problems are
unlikely to arrise anyway, and, for instance, the audio stages
of virtually any superhet receiver could be substituted for
those of the receiver described in the previous chapter with
perfectly adequate results being obtained.
Of course, it would not be a good idea to mix valve and semiconductor
circuitry, and all the circuits in the book employ
semiconductors rather than valves. If one wants the ultimate
in performance from the early stages of the set it is possible
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