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4-6 .
The characteristics of the RC
frequency determining network are such that
the
operating irequency
signal applied to the positive
input of the AMPLIFIER is
1/3 the amplitude of the positive feedback signal.
The phase shift at the operating
frequency
is 09 .
At all
other frequencies the amplitude is less than 1/3
and the
phase shift is other than 09 .
4-9 .
The overall locp gain is the combination of the positive feedback and the oscil
lator gain .
This is equal to unity at the set operating frequency .
4-10 .
PEAK COMPARATOR .
4-11 .
.
The
PEAK COMPARATOR serves two functions .
It sets and maintains the
AMPLIFIER output at 7.2V peak , or 5V rms.
The output is set with the 7.2V refer
ence .
The output is maintained by comparing the output to the 7.2V reference
and
feeding any difference voltage detected to the AGC circuit .
4-12 .
AGC .
4-13 .
The positive feedback to the input of the AMPLIFIER is not exactly one - third
nor is the oscillator gain exactly three for all operating frequencies.
Therefore ,
the purpose of the ACC is to continuously control the oscillator gain to maintain
unity loop gain .
The resistance of the
AGC block can be varied slightly to change
the divider ratio of the negative feedback network .
The variable resistance of the
AGC block is a FET controlled by the error signal from the PEAK COMPARATOR .
Thus any change of the output level causes the PEAK COMPARATOR error signal
to change the resistance of the AGC block which adjusts the oscillator gain to cor
rect for the output level variation .
4-14 .
600 OHM ATTENUATOR .
4-15 .
The
600 OHM ATTENUATOR is a bridged - T connected in such a manner
that the output impedance is 600 ohms regardless of AMPLITUDE setting .
4-2
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