# Questions tagged [amplitude-modulation]

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### Eb/N0 on a VLC simulation using OOK modulation

I have been doing a matlab simulation of a VLC (visible light communication) system that uses OOK for the modulator. I have to explain the basic knowledge behing the simulation and I´m having lots of ...
• 15
1 vote
32 views

### Power of signal in specific frequency in FM and AM modulation

My professor gave us the following problem: Given a sinusoidal signal with $f_m = 1KHz$ which is put into an AM and FM modulation find the modulation index of FM and AM if you know that (amongst ...
17 views

### Message signal and the Envelope of AM wave

Amplitude modulated signal is represented by $$x(t) = (E_c + E_m \cdot \cos(2\pi f_m t)) \cdot \cos(2\pi f_c t).$$ At t=0, we have max. amplitude i.e, Ec + Em. Since the envelope is periodic, I ...
38 views

### Need for rectification in cochlear implants

In cochlear implants, the input signal is fed to a set of bandpass filters and then half wave rectified and low pass filtered to estimate the envelope signal. What is the need for doing rectification? ...
• 93
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### How to Get Started On Demodulating Signals Such As Amplitude Modulation and Pulse Width Modulation

I'm looking to understand how signal modulation/demodulation works. My goal is to be able to demodulate a 315 MHz key fob and be able to tell what buttons are being pressed so I can have a Python ...
1 vote
64 views

### What is the difference between sending pulses and modulating waves?

If you look for amplitude, frequency, phase modulation, you typically get some picture saying you have a wave and you modulate the corresponding parameter (amplitude, frequency, phase). On the other ...
1 vote
61 views

### Mixing with Deformed Local Oscillator Signal

I've decided to build up an AM receiver which is intended to capture sound signals from a nearby broadcasting station that is operating at 954 kHz. I've completed the system design and started to test ...
• 393
100 views

### How Can I correct amplitude and smoothness of FFT?

I am trying to create 10 individual signals with on-off keying modulation format, add them up to have a final signal, and then take a Fourier transform of that signal. I tried to zero padd the final ...
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44 views

### Why does the Superheterodyne AM Receiver use an envelope detector?

I'm currently learning about the Superheterodyne AM Receiver and I don't understand why does it use an envelope detector (as suggested here) rather than taking the signal back to its baseband ...
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• 147
1 vote
37 views

### How to analyze multiple amplitude modulated signals?

What I'm doing is that I send an audio signal consisting of a single frequency into a resonator. To check whether and how the signal has changed I perform a QAM demodulation. I do not need intend to ...
696 views

### Finding the maximum phase and the maximum frequency deviation of an angle-modulated signal

I have an angle-modulated signal: $$s(t)=10\left[\cos\left(10^8\pi · t + 5\sin\left(2\pi\cdot10^3·t\right)\right)\right]$$ How would I go about finding the maximum phase and the maximum frequency ...
287 views

### Fractional Bandwidth of a Gaussian Amplitude Modulated Signal

a gaussian modulated sinusoidal signal may be expressed as $$x(t)=A\cdot e^{(j2\pi ft)}\cdot e^{\left[-\frac{1}{2\sigma^{2}}\cdot(t-t_{0})^{2}\right]}$$ Let's consider the case in which the gaussian ...
• 284
293 views

### Transferring data over sound with QAM / QPSK

Been working on a FSK Modem in the last few weeks and have gotten it to work with 400bps, very reliable, atleast over a virtual audio cable, but it also works when playing a sound directly into a ...
2k views

### FFT of a AM modulated signal

I am generating an AM modulated sinusoidal wave. The carrier frequency is set at $1000 \ \rm Hz$; the modulation frequency is set to $40 \ \rm Hz$ and $100 \%$ of the amplitude is modulated. I ...
• 181
956 views

### Amplitude modulation vs sampling rate?

As a sampled tone's frequency nears $f_s / 2$, amplitude modulation grows apparent: ("Actual" curve in grey; blue is what we get if taking samples (dots) "at face value"). This is ...
• 4,622
153 views

### How harmonics happens when you mix two signals?

Doing a search in quora about Why does Amplitude Modulation have sideband frequencies? i found an answer and within it, a user answered with the following statement: "When you try mixing two ...
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355 views

### Why the bandwidth in frequency spectrum of AM wave is 2fm and not 2fc?

We know, the instantaneous voltage of AM wave is: ...
• 111
30 views

### modulation depth

When a value for the power dissipated by an AM signal is given, and the depth of modulation is also given. Then you are told to find the modulation depth required to increase the power to a higher ...
1 vote
604 views

### Question about Hilbert transform of a cosine signal

In the paper entitled "On instantaneous frequency", it is claimed that the Hilbert transform of a signal in the form of $A(t)cos(\phi(t))$ would result in $A(t)sin(\phi(t))$, where $A(t)$ is ...
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1 vote
71 views

### RF Downconversion using Heterodyne Principle

after a RF down-conversion using heterodyning principle, will there be an information loss? If we translate to a fixed IF frequency, is there is an intuitive way of explain that the information can be ...
• 43
196 views

### Minimum value of G (Amplitude) that guarantees an error probability of at least $10^{-2}$ in a 32-PAM transmission system

pretty much new here. This question comes from an Online course quiz which i have already completed but cant seem to get a good sleep over, just because i cant figure it out. Below is the question ...
70 views

### ZOH non ideal sampling loss formula

Hello i am trying to calculate the amplitude loss of non ideal sampling. My signals amplitude is 10 at 70 frequency. When we sample it at Fs=400 we have al 0.511 loss as shown in plot bellow. How can ...
• 149
46 views

### CDMA scheme that preserves constant envelope (NRZ/ASK shape)

(This is a followup question to Is this a "valid" CDMA modulation?) Is it possible to find a CDMA scheme in which the receiver can only have a simple slicer? In other words, for the ...
• 445
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### Please, help me interpret my Simulink simulation of AM. Why does carrier not appear in the spectogram?

Carrier is 2 * pi * 25, modulating signal is 2 * pi, all the amplitudes are 1s and zero phase. I realized that I could add a sine wave right at the end. I get a carrier in frequency domain, but my ...
• 13
62 views

### What kind of Modulation causes "drops" in FFT Power Spectrum

I am analyzing a signal with FFT and I found an effect, that I do not understand. I am expecting to have an amplitude modulated signal. As far as I know, if you compute the power of the FFT of an ...
• 123
284 views

### Frequency modulation in MATLAB

I am trying to frequency modulate a cosine signal(for assignment). I have written the following code but not getting the required output. ...
• 43
278 views

### Absolute value based AM envelope detection viewed in the frequency domain

In my understanding when a passband AM signal is demodulated with an envelope detector taking the absolute value restores the original baseband version of the signal and the low-pass filter removes ...
• 237
367 views

### Why is the carrier suppressed by AM-DSB-SC modulation?

Lets say I have a message that is a sine wave at 1KHz. As I understand it, I can perform amplitude modulation by multiplying this signal with a carrier, lets say 10KHz, and this process is essentially ...
• 237
1 vote
347 views

### Creating uneven sidebands with AM + PM modulation?

I am trying to modulate an optical signal such that I create a pair of sidebands with arbitrary phase and amplitude with respect to each other. For example I would be like to be able to modulate my ...
1 vote
125 views

### Problem related to phase spectrum of DSB-SC signal

I have tried to solve this question (4.2.3). I got the magnitude spectrum right but the phase spectrum wrong. I am getting the phase spectrum at $\frac{\pi}{4}$ and $- \frac{\pi}{4}$. However, in ...
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1 vote
129 views

### Is there any relation between QAM and streaming?

I am trying to determine whether there is any relation between QAM and streaming (e.g., video streaming). I know that QAM can be used for broadcast TV. I'm not sure if QAM is used for WiFi bit ...
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99 views

### Diode demodulation for AM

What is the capacitor and resistance at output of LPF meant for in the document it was mentioned that it is DC blocker I don't get it can't message contain DC value.
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183 views

### Which equipment to use for testing performance of AM, FM, and DAB

I want to test the performance of AM, FM and DAB radio in RTL-SDR. I want to measure sensitivity, adjacent channel selectivity, cross-modulation/blocking, and third-order intermodulation to be some of ...
1 vote
Required to find symbol error rate vs $E_b/N_0$ for 4QAM, 16QAM & 32QAM. Thought that SER & BER are the same but did my research to find that BER is $1/\log_2(M)$ of SER. Could you please ...