Radio Receivers
Three-point tracking is achieved with

The padder capacitor
Variable selectivity
Double spotting
Double conversion

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Radio Receivers
The local oscillator of a broadcast receiver is tuned to a frequency higher than the incoming frequency

To allow adequate frequency coverage without switching
Because otherwise an intermediate frequency could not be produced
To help the image frequency rejection
To permit easier tracking

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Radio Receivers
If a FET is used as the first AF amplifier in a transistor receiver, this will have the effect of

Improving the selectivity of the receiver
Reducing the effect of noise at low modulation depths
Reducing the effect of negative-peak clipping
Improving the effectiveness of the AGC

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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
stabilization against signal strength variations is provided
the linearity is worse than in phase discriminator
the output is twice that obtainable from a similar phase discriminator

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