Radio Receivers
The frequency generated by each decade in a direct frequency synthesizer is much higher than the frequency shown; this is done to

Increase the frequency stability of the synthesizer
Reduce the spurious frequency problem
Reduce the number of decades
Reduce the number of crystals required

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Radio Receivers
In a ratio detector

the linearity is worse than in phase discriminator
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

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Radio Receivers
In a broadcast superheterodyne receiver, the

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

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