Radio Receivers
The controlled oscillator synthesizer is sometimes preferred over the direct one because

Its frequency stability is better
It does not require crystal oscillator
It is a simpler piece of equipment
It is relatively free of spurious frequency

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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
To permit easier tracking
To help the image frequency rejection
Because otherwise an intermediate frequency could not be produced

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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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Radio Receivers
Indicate the false statement in connection with communications receivers.

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

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