NAVEDTRA 14189A Module 17 Chapter 2 Flashcards
What are the four basic transmitter types?
Am, fm, cw, ssb
What is the function of the oscillator in a cw transmitter?
It generates an rf carrier at a given frequency within required limits
What is the final stage of a transmitter?
Power amplifier
What purpose does a microphone perform in an AM transmitter?
It converts audio (sound) into electrical energy
In an fm transmitter, when does an oscillator generate only a steady frequency?
When no modulation is present
What is a harmonic?
It is an exact multiple of the basic or fundamental frequency
If the fundamental frequency is 200 megahertz, what is the third harmonic?
600 megahertz
Why are frequency multipliers used?
To obtain higher carrier frequencies
What are two advantages of ssb transmission?
It saves power and frequency bandwidth
What is the purpose of an order-wire circuit?
For operator-to-operator service messages and frequency changes
What frequency conversion principle is used to develop the IF?
Heterodyning
What is the function of the detector?
To extract the modulating audio signal
What is the major disadvantage of an fm signal as compared to an AM signal?
Wide bandpass
What two components give a ssb receiver its advantages over an AM
superheterodyne receiver?
A special type of detector and a carrier reinsertion oscillator
What does manual gain control do to strong and weak signals, respectively?
Attenuates the strong and amplifies the weak
What is the purpose of agc/avc in a receiver?
To limit unwanted variations in the output
What is a disadvantage of agc?
Weak signals produce bias, which could result in no usable receiver output
What is the main difference between agc and dagc?
Dagc does not attenuate weak signals
What is the function of the bfo?
It is heterodyned with the rf to produce an audio frequency
What is the purpose of a squelch circuit?
It eliminates noise when no signal is being received
What does a tone control circuit in a receiver do to the audio signal?
It controls the amount of bass and treble response
What is the function of a crystal filter in a receiver?
It is used to achieve maximum selectivity
What is the primary function of an afc circuit?
It is used to accurately control the frequency of the oscillator
