Skip to main content

Modulation Indices for AM, FM, and PM


Modulation index for Amplitude Modulation (AM)

Modulation index in amplitude modulation (AM),

m = Am/Ac

where, Am is the amplitude of the message signal

and     Ac is the amplitude of the carrier signal

 

Modulation index for Frequency Modulation (FM)

Modulation index for FM,
β = kf.Am/fm

where, kf is the frequency sensitivity factor or constant

           Am is the amplitude of the message signal

           fm  is the frequency of the message signal

For Eample, when the value of kf = 2 and Am = 1 & fm = 1 Hz, then frequency deviation is 2 radians.

Then the modulation index for FM will be 2

 

Modulation index for Phase Modulation (PM)

Modulation index in phase modulation (PM),
β = kp.Am = Phase deviation

where, kp is the phase sensitivity factor or constant

           Am is the amplitude of the message signal

For example, when the value of kp = 2 and Am = 1, then phase deviation is 2 radians. Then the modulation index for PM will be 2

 

We know for AM signal, 
Available bandwidth = 2*fm = (fc + fm) - (fc - fm)
where, fm = frequency of the message signal or modulating signal

On the other hand, modulation index = Em / Ec

where, Em is equal to amplitude of modulating signal and Ec denotes amplitude of carrier signal. 


Modulation index is calculated differently for frequency modulation (FM)

Where modulation index = (frequency deviation) / frequency of modulating signal
 Bandwidth = 2*modulating signal (modulation index + 1)

 and for phase modulation (PM), the maximum change in the phase of the carrier signal in accordance with the highest amplitude of the message signal is termed as modulation index.

Q. In AM modulation, if modulation index increases what happens to the bandwidth, transmission power, and noise
A. So, if modulation index increases then there is no change in Bandwidth while the frequencies of modulating signal and carrier signal remain same.

Now, we're coming to the transmission power part,
Pt = Pc (1 + (modulation index)^2)/2 )
where, Pt = transmitted signal power
Pc = power of the carrier signal
As a result, as the modulation index rises, so does the transmission power.

Bandwidth of ASK, FSK, and PSK
Bandwidth of ASK = 2*Rb
Bandwidth of FSK = 2*Rb + f1-f2
Bandwidth of FSK = 2*Rb
where, Rb = bit rate


📊 MATLAB & ONLINE SIMULATIONS (Web-Based)
🎓 GATE & UGC - NET SOLUTIONS
📡 WIRELESS & SIGNAL PROCESSING


Contact Us

Name

Email *

Message *

Popular Posts

CMOS Logic Gates: Inverter, NAND, and NOR

CMOS Logic Gates: Inverter, NAND, and NOR Complementary metal–oxide–semiconductor (CMOS) technology forms the backbone of modern digital IC design. Patented by Frank Wanlass in 1963 ( US patent 3,356,858 ), CMOS enables low-power, high-speed, and noise-immune logic circuits. CMOS gates, including inverters, NAND, and NOR, are widely used in both large-scale and small-scale integrated circuits due to their efficiency and versatility. CMOS Inverter A CMOS inverter consists of a complementary pair of PMOS and NMOS transistors. The PMOS transistor connects to the supply voltage V DD , while the NMOS connects to ground. The input voltage V IN controls both gates, and the output voltage V OUT is taken from the connected drains. CMOS inverters are highly energy-efficient and produce minimal heat due to their comple...
Read more

UGC NET Electronic Science Previous Year Question Papers with Solutions

Download Papers and Solutions Exam Pattern Preparation Tips FAQs More Home / Engineering & Other Exams / UGC NET 2026 PYQ 📊 Exam Highlights: Electronic Science (88) Feature Details Junior Research Fellowship (JRF) ₹37,000 + HRA per month Eligibility M.Sc/M.Tech in Electronics (55%) Validity of Certificate JRF (3 Years) | Lectureship (Lifetime) 📥 Download UGC NET Electronics PDFs Complete collection of previous year question papers, answer keys and explanations for Subject Code 88. Start Downloading 📂 View All Question Papers June 2026 - Question Paper Download PDF June 202...
Read more

OFDM Symbols and Subcarriers Explained

This article explains how OFDM (Orthogonal Frequency Division Multiplexing) symbols and subcarriers work. It covers modulation, mapping symbols to subcarriers, subcarrier frequency spacing, IFFT synthesis, cyclic prefix, and transmission. Step 1: Modulation First, modulate the input bitstream. For example, with 16-QAM , each group of 4 bits maps to one QAM symbol. Suppose we generate a sequence of QAM symbols: s0, s1, s2, s3, s4, s5, …, s63 Step 2: Mapping Symbols to Subcarriers Assume N sub = 8 subcarriers. Each OFDM symbol in the frequency domain contains 8 QAM symbols (one per subcarrier): Mapping (example) OFDM symbol 1 → s0, s1, s2, s3, s4, s5, s6, s7 OFDM symbol 2 → s8, s9, s10, s11, s12, s13, s14, s15 … OFDM sym...
Read more

IIR Filter Simulation

IIR Filter & Feedback Lab IIR Filter & Feedback Lab Exploring Recursive Systems: Where Output depends on Output 1 Input Signal $x[n]$ Signal Type Unit Impulse δ[n] Sine Wave Unit Step u[n] Frequency (for Sine) Notice: With an Impulse input, the output of an IIR filter can ring forever (Infinite response). 2 Feedback Coefficients Numerator $b$ (Feed-forward) Denominator $a$ (Feedback - $a_0$ is always 1) System Stable Try setting $a$ to 1.0, -1.1 to see an unstable system! ...
Read more

(Filters) Free MATLAB alternative for signal analysis

Advanced Signal Filters Upload CSV (1st Col) or Audio (WAV, MP3, etc.) Generate Messy Signal (20Hz + 50Hz + 150Hz) No Operation FFT (Spectrum) Amplitude Modulation (AM) Double Sideband Supressed Carrier (DSBSC) Pulse Amplitude Modulation (PAM) Flat Top PAM Filters - LPF, HPF, BPF, Notch Principal Component Analysis (PCA) Cross Spectrum Filter Type: Signal Cleaner ...
Read more

Decision Feedback Equalizer (DFE) in MATLAB

  MATLAB Code M = 4; % QPSK numSymbols = 10000; numTrainingSymbols = 5000; chtaps = [1 0.5*exp(1i*pi/6) 0.1*exp(-1i*pi/8)]; % Generate QPSK symbols data = randi([0 M-1], numSymbols, 1); tx = pskmod(data, M, pi/4); % DFE setup eq = comm.DecisionFeedbackEqualizer; eq.ReferenceTap = 1; eq.NumForwardTaps = 5; eq.NumFeedbackTaps = 3; % SNR sweep snrVec = 0:5:25; % 0,5,10,...25 dB berBefore = zeros(size(snrVec)); berAfter = zeros(size(snrVec)); for k = 1:length(snrVec) % Apply channel and AWGN rx = awgn(filter(chtaps,1,tx), snrVec(k), 'measured' ); % BER before equalization rxDataNoEq = pskdemod(rx, M, pi/4); [~, berBefore(k)] = biterr(data, rxDataNoEq); % Equalize [y,~,~] = eq(rx, tx(1:numTrainingSymbols)); % Phase correction phaseOffset = angle(mean(conj(tx(1:numTrainingSymbols)) .* y(1:numTrainingSymbols))); yCorrected = y * exp(-1i*phaseOffset); % BER after equalization rxDataEq = pskdemod(yCorrected, M, pi/4); [...
Read more

The electric field of a monochromatic plane wave travelling in a lossless isotropic and homogenous medium is given by E(z, t) = ...

  Q. The electric field of a monochromatic plane wave travelling in a lossless isotropic and homogenous medium is given by E(z, t) = E₀ [x̂ cos(ωt − kz) + Å· sin(ωt − kz)] in a right-handed orthogonal co-ordinate system. Which of the following is the correct polarization of the electromagnetic wave? (A) Right-handed circularly polarized Correct answer under the IEEE convention. (B) Left-handed circularly polarized (C) Linearly polarized (D) Linearly polarized at −45° to x̂ Solution 1. Identify the electric-field components Let ψ = ωt − kz. The components along the x and y directions are: Eâ‚“ = E₀ cos ψ Eᵧ = E₀ sin ψ Both components have equal amplitudes, the same frequency, and a phase difference of 90°. These are the conditions for circular polarization. ...
Read more

Online Simulator for Frequency Modulatiuon and Demodulation

FM Modulation Simulator Frequency Modulation (FM) In Frequency Modulation, the frequency of the carrier signal varies in accordance with the message signal's amplitude. s FM (t) = A c cos(ω c t + k f ∫m(t)dt) where ω = 2Ï€f & k f = Frequency Sensitivity Modulation index, β = (k f * A m ) / f m Change the parameter values to see the effect. Message Freq (Hz) 1 Carrier Freq (Hz) Message Amplitude (Am) Kf (sensitivity): 50 Perform FM Demodulation 🧪 Experiment for Students: ...
Read more