Hint: FSK (Frequency Shift Keying) = digital control

FSK is a method of rapidly changing the carrier frequency of a transmitter between two different frequencies. These two carrier frequencies are often referred to as the Mark frequency and the Space frequency, or simply Mark and Space. FSK is commonly used for RTTY (radioteletype) as well as ASCII-based transmissions like packet. Since there are only two frequencies to generate, a digital control signal is used. The terms digital, binary, ON-OFF, and two-state are all basically equivalent. This two-state control signal can be used to shift the frequency of an oscillator back and forth between a Mark frequency and a Space frequency. After appropriate amplification, the carrier signal generated by the oscillator can leave the transmitter to energize an antenna.

Quick and dirty mnemonic: "F"requency "S"ignal "K"ontrol.

Silly hint; the correct answer is the only one that has the word "direct" in the answer.

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(B). Phase modulation is the name of the process that changes the phase angle of an RF wave to convey information. Phase modulation changes the signal by modifying the instantaneous phase angle of the carrier. PM is often used for data transmission methods such as PSK (phase-shift keying).

For more info see Wikipedia: Phase modulation

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Hint: modulate CONVEYs & controls

Frequency modulation (FM) is the process which changes the frequency of an RF wave to convey information. The instantaneous frequency of the carrier is altered to convey the information, while the amplitude remains constant. FM is used for frequency-shift keying, radar in addition to radio voice transmissions.

For more info see Wikipedia: Frequency modulation

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Hint: PHASE MODULATION is produced by REACTANCE

Phase modulation is the emission produced by a reactance modulator connected to an RF power amplifier. The reactance modulator changes the instantaneous phase angle of the carrier, generating phase modulated signals.

Silly hint: The child REACTED because they were going through a PHASE.

For more info see Wikipedia: Phase modulation

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Hint: “Amplitude” is the power level of RF.

(D). Amplitude modulation (AM) is the type of modulation that varies the instantaneous power level of the RF signal. The power or signal strength of the wave is measured as the wave amplitude (may also be called the envelope).

For more info see Wikipedia: Amplitude modulation (AM)

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(C). One advantage of carrier suppression in a single-sideband phone transmission is the available transmitter power can be used more effectively.

Each section of the band uses a portion of the total power. So for each portion of the signal that is suppressed (i.e. not using a portion of the total power), that power is now available for the remainder of the signal.

So if the carrier is suppressed, the power that would have been used for that portion of the signal may now be used for transmitting the sideband more effectively.

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(A). Single sideband is the phone emission which uses the narrowest frequency bandwidth. For each part of the signal that is suppressed, the bandwidth will be reduced. By supressing the carrier and filtering the unwanted sideband, the typical bandwidth of a single-sideband signal is reduced to only about 3 kHz.

For more info see Wikipedia: single-sideband (SSB)

Hint: Single is less than double.

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Excessive bandwidth is an effect of over-modulation. Overmodulating the signal causes increased distortion or deviation of the waveform. This increases the formation of spurious emissions with distortion outside the normal bandwidth.

For more info see Wikipedia: Overmodulation

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The transmit audio or microphone gain is typically adjusted for proper ALC setting on an amateur single sideband transceiver.

ALC (Automatic Level Control) is a self-controlling transmitter circuit that attempts to maintain a constant level of output power by automatically adjusting the gain of the final amplifier, to prevent it from overloading and damaging the final stage by excessive drive. An operator would adjust the input signal, which is the microphone gain (the transmitted audio) to ensure that the ALC is set appropriately for SSB.

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Flat-topping (or clipping) is where overmodulation causes a distortion of the waveform in which the amplitude appears flattened on the oscilloscope, because the maximum levels of output voltage or current are exceeded.

For more info see Wikipedia: Flat-topping or Clipping

(Hint: You will DRIVE faster when on FLAT ground.) {OR} You drive on a flattop slang for a road)

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Hint: Think of an envelope's four corners, these would be the peak values.

In AM, the frequency is stable and only the amplitude modulates (Amplitude Modulation). When this happens, the carrier signal's peak value will change during modulation. In FM, the signal's peak value remains constant.

Amplitude Modulation

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