Radio Receivers
The controlled oscillator synthesizer is sometimes preferred over the direct one because

It is a simpler piece of equipment
It does not require crystal oscillator
It is relatively free of spurious frequency
Its frequency stability is better

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Radio Receivers
In a radio receiver with simple AGC

An increase in signal strength produces more AGC
The audio stage gain is normally controlled by the AGC
The faster the AGC time constant the more accurate the output
The highest AGC voltage is produced

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Radio Receivers
In a ratio detector

the linearity is worse than in phase discriminator
the output is twice that obtainable from a similar phase discriminator
stabilization against signal strength variations is provided
the circuit is the same as in a discriminator, except that the diodes are reversed

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