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
Indicate the false statement in connection with communications receivers.

Double conversion is used to improve image rejection
The noise limiter cuts off the receiver’s output during a noise pulse.
Variable sensitivity is used to eliminate selective fading
A product demodulator could be used for the reception of Morse code.

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Radio Receivers
In a ratio detector

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

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