Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes Calculators Education Engineering Magazine Articles Engineering software RF Cafe Archives Magazine Sponsor RF Cafe Sponsor Links Saturday Evening Post NEETS EW Radar Handbook Microwave Museum About RF Cafe Aegis Power Systems Alliance Test Equipment Centric RF Empower RF ISOTEC Reactel RF Connector Technology San Francisco Circuits Anritsu Amplifier Solutions Anatech Electronics Axiom Test Equipment Conduct RF Copper Mountain Technologies Exodus Advanced Communications Innovative Power Products KR Filters LadyBug Technologies Rigol TotalTemp Technologies Werbel Microwave Windfreak Technologies Wireless Telecom Group Withwave RF Cafe Software Resources Vintage Magazines RF Cafe Software WhoIs entry for RF Cafe.com Thank you for visiting RF Cafe!
Rigol DHO1000 Oscilloscope - RF Cafe

RF Cascade Workbook 2018 by RF Cafe

Exodus Advanced Communications Best in Class RF Amplifier SSPAs

Please Support RF Cafe by purchasing my  ridiculously low-priced products, all of which I created.

RF Cascade Workbook for Excel

RF & Electronics Symbols for Visio

RF & Electronics Symbols for Office

RF & Electronics Stencils for Visio

RF Workbench

T-Shirts, Mugs, Cups, Ball Caps, Mouse Pads

These Are Available for Free

Espresso Engineering Workbook™

Smith Chart™ for Excel

Crane Aerospace Electronics Microwave Solutions: Space Qualified Passive Products

Amplitude Modulation

Crosley 03CB restored radio electronics chassis - RF CafeCrosley 03CB restored radio - RF CafeAmplitude modulation uses the instantaneous amplitude of a modulating signal (voice, music, data, etc.) to directly vary the amplitude of a carrier signal. Modulation index, m, is used to describe the ratio of maximum voltage to minimum voltage in the modulated signal. If the modulating signal is equal in magnitude to the carrier, then m = 1 and the modulated signal varies from a scaled maximum of unity down to zero (see figure below). When m = 0, no modulation of the carrier is performed. If m is greater than 1, the carrier is actually cut off for some period of time, and unwanted harmonics are created at the transmitter output.

The pictures here are of my restored Crosley 03CB radio, which was manufactured in 1941, before commercial FM broadcast radio was still in the experimental phase of development. This radio tuned the 540 to 1700 kHz AM band and the 16 to 49 meter shortwave band.

Class Conduction

Angle

Maximum

Efficiency

Description
A 360º 25% Device is biased in to conduct in the linear region all the time.
AB > 180º,

<< 360º

--- Two devices connected like a Class B, but biased to conduct somewhere between Class A and Class B.
B 180º 78.5% Two devices in series with the output taken at the common junction. Both devices biased to conduct in the linear region for opposite half a cycle, i.e., they are never on at the same time.
C > 0º,

< 180º

--- Device is biased to turn on after a certain input threshold voltage is exceeded. Very efficient, but creates distortion.
D   100% Used to switch completely on or completely off.
E     Used for rectangular input signals.

In the frequency domain, the carrier frequency is flanked on both sides by mirror image copies of the modulating signal.

M1 = Ωc ± ωm1, ΩM2 = Ωc ± Ωm2

Frequency modulation (FM) spectrum - RF Cafe

AM General Equation

Let the carrier be xc(t) = Xc·sin (Ωct), and the modulating signal be xm(t) = Xm·sin (ωmt)

Then   x(t) = Xc·[1+m·sin (Ωmt)]·sin (Ωct)

Modulation Index

Modulation Index formula - RF Cafe

In the following examples, the carrier frequency is nine times the modulation frequency. Red (dashed) lines represent the modulation envelope. Blue (solid) lines represent the modulated carrier.

100% Modulation

100% amplitude modulation (AM) graph - RF CafeHere, the maximum voltage (Vmax) is 2 V and the minimum (Vmin) is 0 V. From the modulation index formula:

Modulation Index formula (m=1) - RF Cafe

50% Modulation

50% amplitude modulation (AM) graph - RF CafeHere, the maximum voltage (Vmax) is 3 V and the minimum (Vmin) is 1 V. From the modulation index formula:

Modulation Index formula (m=0.5) - RF Cafe

25% Modulation

25% amplitude modulation (AM) graph - RF CafeHere, the maximum voltage (Vmax) is 1.25 V and the minimum (Vmin) is 0.75 V. From the modulation index formula:

Modulation Index formula (m=0.25) - RF Cafe

150% Modulation

150% amplitude modulation (AM) graph - RF CafeHere, the maximum voltage (Vmax) is 2.5 V and the minimum (Vmin) is -0.5 V. From the modulation index formula:

Modulation Index formula (m=1.5) - RF Cafe

Note: AM waveforms created with MathCAD 4.0 software.

Related Pages on RF Cafe

- Amplitude Modulation

- Frequency Modulation

- Quadrature (I/Q) Modulator Sideband Suppression

- Bessel Functions & Graphs

- Modulation Principles, AM Modulation, NEETS

- Modulation Principles, FM Modulation, NEETS

- Modulation Principles, Demodulation, NEETS

- Frequency Mixer, Converter, Multiplier, Modulator Vendors

Crane Aerospace Electronics Microwave Solutions: Space Qualified Passive Products
ConductRF Phased Matched RF Cables - RF Cafe

Windfreak Technologies Frequency Synthesizers - RF Cafe

Noisecom