AM Fundamentals and Principles - Module 3

Vocabulary practice flashcards covering fundamental definitions, circuits, bandwidth rules, signal equations, and modulation index calculations for Amplitude Modulation (AM).

Modulation

The process of varying one or more properties of a periodic waveform called the carrier signal with a modulating signal.

Modulating Signal

Also called the intelligence signal or baseband signal, this is the signal that contains the information to be transmitted.

Amplitude Modulation (AM)

A type of modulation where the carrier signal's frequency remains constant while its amplitude varies in accordance with the amplitude and frequency of the information signal.

Oscillator

A device used in a transmitter to generate a high-frequency carrier signal.

Multiplier

A device used to introduce the information signal to the carrier signal.

Envelope

The imaginary dashed line connecting the positive and negative peaks of a modulated signal, which gives the exact shape of the modulating signal.

Modulator

The circuit used to produce an AM wave by changing a lower-frequency baseband signal to a higher-frequency signal.

Demodulator

Also called a detector, it is the circuit used at the receiving end to recover the original intelligence signal from an AM wave.

Modulation Index ($m$)

Mathematically expressed as the ratio between the peak voltage of the modulating signal ($V_m$) and the peak voltage of the carrier signal ($V_c$), represented as $m = \frac{V_m}{V_c}$.

Percentage Modulation

The modulation index ($m$) multiplied by $100$.

Overmodulation

A condition occurring when the modulating voltage is greater than the carrier voltage, resulting in a modulation index greater than $1$ and causing distortion of the intelligence signal at the receiver.

AM Bandwidth Allocation

The bandwidth allocated to an AM radio station by the NTC, which is $10\,\text{kHz}$ (twice the $5000\,\text{Hz}$ bandwidth of an audio signal).

AM Carrier Frequency Range

The allowable carrier frequency range for AM stations, between $530\,\text{kHz}$ and $1700\,\text{kHz}$ ($1.7\,\text{MHz}$), separated from adjacent stations by at least $10\,\text{kHz}$.

Modulating Signal Instantaneous Voltage Equation

Expressed mathematically as $v_m = V_m \sin(2\pi f_m t)$, where $v_m$ is the instantaneous value, $V_m$ is the peak amplitude, and $f_m$ is the frequency of the modulating signal.

Carrier Signal Instantaneous Voltage Equation

Expressed mathematically as $v_c = V_c \sin(2\pi f_c t)$, where $v_c$ is the instantaneous value, $V_c$ is the peak amplitude, and $f_c$ is the frequency of the carrier signal.

Envelope Instantaneous Voltage Equation ($v_1$)

The equation for the instantaneous value of the top and bottom voltage envelope, expressed as $v_1 = V_c + v_m = V_c + V_m \sin(2\pi f_m t)$.

Modulated Wave Instantaneous Voltage Equation ($v_2$)

The complete instantaneous voltage equation of the AM wave, expressed as $v_2 = V_c \sin(2\pi f_c t) + (V_m \sin(2\pi f_m t))(\sin(2\pi f_c t))$.

Peak Modulating Voltage from Envelope ($V_m$)

Calculated from oscilloscope measurements of an AM signal using the formula $V_m = \frac{V_{\text{max}} - V_{\text{min}}}{2}$.

Peak Carrier Voltage from Envelope ($V_c$)

Calculated from oscilloscope measurements of an AM signal using the formula $V_c = \frac{V_{\text{max}} + V_{\text{min}}}{2}$.

Modulation Index Formula via Envelope Peaks

The formula used to calculate modulation index $m$ directly from envelope voltage measurements: $m = \frac{V_{\text{max}} - V_{\text{min}}}{V_{\text{max}} + V_{\text{min}}}$.