Radio Receivers
One of the main functions of the RF amplifier in a superheterodyne receiver is to

Increase the tuning range of the receiver
Permit better adjacent-channel rejection
Improve the rejection of the image frequency
Provide improved tracking

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Radio Receivers
In a ratio detector

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

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