# Questions tagged [amplitude-modulation]

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### Why Hilbert Transform is terrible choice for amplitude demodulation of broadband signals?

A reference answer empirically demonstrates that Hilbert envelope does not work well for the (amplitude) demodulation of a broadband signal. I am looking for the math which explains why...
• 1,084
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### Deriving SER & BER for 4QAM, 16QAM and 32QAM

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 ...
924 views

### Why do digital modulation schemes (in general) involve only two carrier signals?

In my digital communication, class we have covered the various modulation schemes, namely QAM and its derivatives (B(A/P)SK, PAM and (Q/M)PSK) as well as BFSK. These two schemes have one or at most ...
747 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 ...
• 308
5k 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 ...
• 191
2k 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 ...
• 8,815
458 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
246 views

### Why complex signal doesn't remove "beatings" while sampling?

My motivation to this post has arisen from the accepted answer to Amplitude modulation vs sampling rate? Sampling the signal with the frequency close to $f_s/2$ can lead to some kind of "beatings&...
• 355
841 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 ...
• 324
1 vote
302 views

### Why Does ASK Modulation Create Fourier Sidebands?

I know why analog amplitude modulation has side bands, it is related to (fc+fd) and (fc-fd). But what about DAM? ASK(DAM) is a type of digital modulation, and there are only two state: carrier signal ...
1 vote
124 views

### Why don't I hear the carrier wave or higher-pitched audio when tuning slightly away from the center of an AM station?

Let's say I'm listening to an AM radio station in the United States at 680 kHz. From my understanding that means there's a carrier wave at 680 kHz and the bandwidth for the station goes from 675 kHz ...
1 vote
161 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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1 vote
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### 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 ...
• 573
1 vote
2k views

### How do I determine the carrier frequency of a given AM signal?

I am trying to figure out what the carrier frequency of a signal is given only its discrete-time domain information and the fact that it is a signal on the AM radio frequency band(550 - 1700kHz). Is ...
1 vote
49 views

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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 ...
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### 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 ...
• 267
428 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
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### 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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### How does PAM-4 encoding of a digital signal relate to theoretical *pulse* amplitude modulation?

Pulse amplitude modulation in general is often explained using plots like this one from wikipedia: There is a sinusoid analog signal (red) to be "imprinted" on a train of pulses. The result ...
• 101
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### I don't understand which signal I should use as a carrier in my excersise

$\DeclareMathOperator{\sinc}{sinc}$ Given 3 signals $x_1(t) = \sinc(t) , x_2(t) = 10\cos(2\pi f_2t)$ and $x_3(t) = 5\cos(2\pi f_1t)$, where $f_2 = 100\text{ kHz}$ and $f_1 = 1\text{ kHz}$. I must ...
79 views

### Bandwidth of amplitude-modulated wave with triangular envelope

I have the following wave: I know that it is demodulated by an envelope detector whose source resistance is 0Ohm and its load resistance is 250Ohm. Now, I need to calculate a C capacitor in order ...
174 views

### Need for rectification in cochlear implants

In cochlear implants, the input signal is fed to a set of bandpass filters and is then half-wave rectified and low pass filtered to estimate the envelope signal. What is the need for doing ...
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### 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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369 views

### Phasor diagram of Phase modulated signal

While studying the phasor diagrams of Amplitude modulation and Frequency modulation, I am stuck at a problem involving the phasor diagram of an angle modulated signal whose equation is given by s(t) ...
187 views

### How to compute a complex modulated signal from an audio file?

I have a 30-seconds wav audio file with a sample rate of 44100Hz, obviously this array of samples is a 1D array, and so when I modulate it in AM (Amplitude Modulation) I get back a 1D array, but I ...
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105 views

### How to choose frequency of local oscillator for heterodyne principal

I am trying to implement the heterodyne principle in order to make an AM signal demodulator that can demodulate signals on a set bandwidth(550 - 1720kHz). Is there a formula or some other method of ...
119 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 ...
• 171
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### 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 ...
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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 ...
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### What is the name for amplitude variation over time with angle measurement called?

I am trying to create a method in my real-time algorithm to measure the variation in time based on a simple technique to avoid a huge overhead in the processing on the hardware. The first method I am ...
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