Signal Processing Stack Exchange
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Questions tagged [modulation]

Modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with the amplitude of low-frequence modulating signal which typically contains information to be transmitted.

The three key parameters of a periodic waveform are its amplitude ("volume"), its phase ("timing") and its frequency ("pitch"). Any of these properties can be modified in accordance with a low frequency signal to obtain the modulated signal. Typically a high-frequency sinusoid waveform is used as carrier signal, but a square wave pulse train may also be used.

Source: Wikipedia.

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Why does QAM modulation produce asymmetric sidebands?

With amplitude modulation the signal only has a real component and the modulated signal has two sidebands that are symmetric around the carrier frequency. My understanding is that in QAM the sidebands are necessarily not symmetric. The point of…
Chris_F
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Up-converting a sinusoidal signal

I want to up-convert a baseband sinusoidal signal of frequency $4000 \, \rm{Hz}$ using a carrier frequency of $20\, \rm{KHz}$. I read that one can up-convert a baseband signal to a passband signal using the following. But after convolution with a…
JayHeo
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Understanding I and Q modulation

As a newbie I am trying to understand I and Q modulation and demodulation. So from what I read the I and Q components of a signal separately mix with RF signals that are 90 degrees out of phase with each other and then the summation is transmitted…
Jack
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Is there a way to calculate modulation depth after the modulation process?

Suppose I have some amplitude modulated carrier wave $x$. If I have no access to the original message wave nor the unmodulated carrier, is it some how possible to calculate what is the modulation depth of $x$? If I have understood this correctly,…
wireless
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About FM signal's proving

My text book (Communication Systems analysis and design P.334, 335) have a FM signal is $s_{FM}(t) = A cos[2\pi[f_c+ks(t)]t+\phi]$ where k is a constant and $\phi$ is the arbitrary phase angles then the textbook suggest while in FM,…
Samuel
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Difference between Line Code and Keying

The following statements are from Wikipedia page of Keying Keying or digital modulation applies to transmitting a digital signal over an analogue passband channel. When a digital signal is to be transmitted over an analogue baseband channel,…
GypsyCosmonaut
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How should I decode Pulse Density Modulation signal?

I'm trying to learn the concept of Pulse-density Modulation. The wiki page gives a good overview and pseudocode of encoding procedure, but it lacks the decoding part: The process of decoding a PDM signal into an analog one is simple: one only has…
Yurii A
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NRZ vs. Manchester pulse shaping filter (Modulator)

I'm trying to visualize the differences on the output waveform of a modulator when using NRZ or a Manchester pulse shaping filter. To keep it simple, let's think of a binary PAM signal with an input bit sequence 101011. My thoughts are that with a…
Kyle Weller
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Direct sequence spread spectrum modulation

When the receiver gets the signal $m_t$ sent by the transmitter, the signal will have an additive interference $i_t$. Thereby signal received will be : $$r_t = m_t + i_t$$ I know that to get back the data from the signal, we have to multiply by the…
Benoit de Patoul
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Frequency shifting property

Usually in radio systems in order to move the frequency response of the message signal to a new frequency band centered at f, the message signal is mixed with $\cos(2\pi ft)$. What would change in frequency if we multiply the message signal to …
Jack
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Why does NB-IoT use standard QPSK in multi-tone transmission, when pi/4 QPSK is implemented for single-tone?

I've been studying the modulation schemes used in NB-IoT communication, with a particular focus on energy efficiency. I've noticed that QPSK (Quadrature Phase Shift Keying) is used in multi-tone transmission, while π/4-QPSK is often used in…
Guus
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Meaning of complex envelope in simple terms?

I tried to find a simple explanation of what a complex envelope of a signal is, with no luck. I'm looking for an explanation with simple terms, and possibly that is easy to visualize or imagine, so that I can grab the main concept. To give some…
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Why would amplitude modulation result in change of frequency?

Question: (single choice correct; source: JEE Main 2015) A signal of $5 kHz$ frequency is amplitude modulated on a carrier wave of frequency $2 MHz$. The frequencies of the resultant signal is/are: 2 MHz only 2005 kHz, and 1995 kHz 2005 kHz, 2000…
Gaurang Tandon
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How does modulation work in simple language?

I am reading modulation from this site (am a beginner). In the end, they've given this example: I am having trouble understanding how exactly they arrived at the two modulated results for AM and FM. I have attempted to understand it, and this is my…
Gaurang Tandon
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What is the phase coded modulation?

I'm trying to understand what is the "phase coded modulation" and how does it work. As far as I know, Although the linear frequency modulated (LFM) waveform continues to be the workhorse of modern radars, there is growing interest in the use…
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