Chapter 4: Amplitude Modulation Transmission - Tomasi Review

Modulation

The process of impressing low-frequency information signals into a high-frequency carrier signal.

Demodulation

The reverse process of modulation where the received signals are transformed back to their original form.

Amplitude Modulation

The process of changing the amplitude of a relatively high frequency carrier signal in proportion with the instantaneous value of the modulating signal.

Radio Frequencies

Frequencies that are high enough to be efficiently radiated by the antenna and propagated through free space.

AM Envelope

The modulated output waveform from an AM modulator.

AM DSBFC

Sometimes called conventional AM or simply AM.

Lower Sideband

The band of frequencies between fc-fm(max).

Lower Side Frequency

Any frequency within the lower sideband.

Upper sideband

The band of frequencies between fc and fc + fm(max).

Upper Side Frequency

Any frequency within the upper sideband.

Coefficient of Modulation

The term used to describe amount of amplitude change (modulation) present in an AM waveform signal.

Percent Modulation

The coefficient of modulation stated as a percentage.

100%

The maximum percent modulation that can be imposed without causing excessive distortion.

Location

The __________in a transmitter where modulation occurs determines whether the circuit is a low or a high-level transmitter.

Low-Level Modulation

The modulation takes place prior to the output element of the final stage of the transmitter.

High-Level Modulation

The modulation takes place in the final element of the final stage where the carrier signal is at its maximum amplitute.

Emitter Modulation

The amplitude of the output signal depends on the amplitude of the inner carrier and the voltage gain of the amplifier.

Collector Modulator

A class C modulator capable of nonlinear mixing and the modulating signal is applied directly to the collector.

Up-converter

Used to translate the low-frequency intelligence signals to radio-frequency signals that can be efficiently radiated from an antenna and propagated through free space.

Trapezoidal Pattern

Are used for observing the modulation characteristics of AM transmitters.

Carrier Shift

A form of amplitude distortion introduced when the positive and negative alternations in the AM modulated signal are not equal (nonsymmetrical modulation).

Nonsinusoidal Signals

Complex waveforms comprised of two or more frequencies.

Complex Repetitive Waveforms

Are complex waves made up of two or more harmonically related sine waves and include square, rectangular, and triangular waves.

Quadrature Amplitude Modulation ( QAM )

A form of AM where signals from two separate information sources modulate the same carrier frequency at the same time without interfering with each other. The information sources modulate the same carrier after it has been separated into two carrier signals that are 90 out of phase with each other.