tor in the generators which derive power from 115-volt AC sources.
In portable
generators, battery power supplies are usually used, and these require no voltage
regulation.
c. In the audio and video generators of the beat-frequency type, the output
frequency is produced by mixing the signals of two radio frequency oscillators, one
of which is fixed in frequency and the other variable. The difference in frequency
of the two is equal to the desired audio or video frequency.
(1) Audio signal generators often include RC oscillators in which the audio
frequency is directly produced.
In these a resistance-capacitance circuit is the
frequency-determining part of the oscillator. The frequency varies when either the
resistance or the capacitance is changed in value.
(2) In commercial generators, however, the capacitance alone is often
chosen as the variable element. The change in frequency which can be produced by
this method is limited, and it is usually necessary to cover the entire range of
the generator in steps.
This is accomplished by providing several RC circuits,
each corresponding to a portion of the entire range of frequency values.
The
circuits in the oscillator are switched one at a time to give the desired portion
of the audio range.
d. The amplifier section of the block diagram (fig 3-2) usually consists of a
voltage amplifier and one or two power amplifiers. These are coupled by means of
RC networks, and the output of the final power amplifier is often coupled to the
attenuator, or output control, by means of an output transformer.
Figure 3-2.
Block diagram of audio or video signal generator
e. The output control section provides a means of matching the output signal
to the input of the equipment under test and regulating the amplitude of the
signal.
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