Radio Receivers
In a broadcast superheterodyne receiver, the

Local oscillator frequency is normally double the IF
RF amplifier normally works at 455 kHz above the carrier frequency
Mixer input must be tuned to the signal frequency
Local oscillator operates below the signal frequency

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Radio Receivers
In a ratio detector

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
the linearity is worse than in phase discriminator

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