Questions tagged [demodulation]

Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave.

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115 views

Detecting I/Q imbalance

Are there any methods of detecting, measuring, and/or estimating I/Q imbalance (from, say, an upstream quadrature mixer and/or ADC), without using or having a controlled test signal (other than ...
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51 views

BPSK demodulation [duplicate]

For experimental reasons i created a function that helps me to modulate a signal using BPSK, the input signal is {1,1,0,1,0} and it works fine ...
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337 views

Removing I/Q phase rotation

What is the most reliable and agnostic way to correct for a phase rotation of I/Q downconversion - without time alignment of the signal and support different lengths of transmitted and received data? ...
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0answers
89 views

Does anyone recognize this modulation?

I'm trying to extract the code of my garage remote, but i have some difficulty to find witch modulation has been used. At first I thought it was a simple digital modulation, but there is some strange ...
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1answer
533 views

Square law demodulator. How can we eliminate the term containing $m^2(t)$?

We are trying to extract the message signal from the AM signal using square law demodulator. In the final expression, $V_2(t)$, the term encircled in blue has to be retained, and the others have to ...
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1answer
304 views

AM demodulation from a real RF signal

I'm capturing an RF signal transmitted at 433.8MHz, with a bandwidth of about 50KHz. My goal is to be able to save it as a .wav file. I'm using an RTL-SDR dongle and a software named HDSDR, where I ...
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4k views

AM Modulator Demodulator in Python

I am trying to make a AM modem using Python Numpy and Matplotlib. I am successful in generating the AM Signal but I cannot demodulate it using a lowpass filter function that I made. The demodulation ...
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2answers
352 views

Mystery signal - FSK, BPSK?

I have a mystery audio signal that I need to decode, it's from a discontinued product. Inspecting the object code shows a module called decodeFSK so that suggests ...
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1answer
510 views

Prepare IQ Data for Goertzel Algorithm

I have a quadrature (IQ - 0..255) data byte stream that I receive from an rtl-sdr dongle as IQIQIQIQ..... That means that negative values are < 128 and positive values >= 128 I am attempting to ...
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1answer
682 views

Extracting the carrier signal from AM

I am new to DSP and leaning about amplitude modulation. I am trying to demodulate a 5 Hz signal that is modulated by a 50 Hz carrier. I am trying to extract the carrier, not the the 5 Hz signal. A ...
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1answer
32 views

How to model airborne sound channel

I'm making a soft demodulation/decoding to communicate a microphone and a speaker in short range. I have to calculate the LLR using my constellation and the airborne sound channel probability density ...
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1answer
320 views

FM demodulation

I have a frequency modulated signal. My problem is the following: The sidebands are asymmetric. Meaning that the amplitudes of the sidebands left and right are not equal. Does anyone know what this ...
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1answer
199 views

How to calculate baudrate?

I'm going through this article https://www.elttam.com.au/blog/intro-sdr-and-rf-analysis/ and I find it hard to understand the following part: However, in our case we might want to transmit this ...
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2answers
144 views

mpsk demodulation using digital sample

I am trying to receive and demodulate a 8PSK modulated sinusoidal waveform (real not complex) which is constant envelop and changing only in phase of the continuous sinusoid carrier every Symbol ...
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1answer
249 views

Recovering DSSS signal from below noise Floor

I want to understand what actually happens in the direct sequence spread spectrum demodulator ? Why is it said that the signal is recovered from below the noise floor ? Can someone please explain the ...
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2answers
564 views

Demodulating AM signal from carrier signal on Matlab

I'm trying to demodulate a voice signal (bandwidth approximately 5 kHz) from a carrier signal (100kHz). [y,Fs]=audioread('Signal1.wav'); h=10*sinc(10*(-10:10)); y1=filter(h,1,y); But ...
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1answer
151 views

How is a signal with SNR less than unity demodulated?

The title pretty much says it all. What technique can be used to demodulate a signal with SNR less than 1?
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1answer
709 views

Demodulation on noise

I'm new in DSP, and I'm working on dsp application involving machinery (Diagnostics based on noise), and to do this I need to make DEMON processing. I want to process the signal like in the picture (...
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1answer
2k views

Downconverting real signal to IQ baseband

Despite reading various answers on this site and on other sites I am still confused about how to convert a real-valued signal back down to its original IQ baseband values. Note I am still a beginner ...
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47 views

Mathematics in selection of RC time constant for an envelope detector for AM

Let the capacitor be charged to voltage $ V(t_0) $ at $ t=t_0 $ and then start discharging. At time $ t \, (>t_0)$, the delayed capacitor voltage is $$ v(t)=V(t_0)\operatorname{exp}(- \frac{t-t_0}{...
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1answer
301 views

Distortion in demodulation signal

I'm doing amplitude modulation and demodulation for DSB. the maximum amplitude of my original signal is $1$. After demodulating the signal, I should be getting the original signal which is $1$ but ...
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2answers
401 views

How to demodulate DSB-SC

I need help with demodulating DSB-SC signals. I took the appproach of using the FFT as follows: I have a signal. I FFT it. Then i take real and imaginary part of the FFT and translate some values: <...
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0answers
112 views

How to find and fix the delay of a modulation

I am creating a model in MATLAB to simulate power line communication, but I found a problem. I'm very new to the DSP area, I get my code below from a MATLAB example. ...
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0answers
427 views

Demodulation distortion in single-sideband and double-sideband

I am trying to compare the demodulation for single sideband (SSB) and dual sideband modulation formats (DSB) when the reconstructed carrier is not perfect (i.e. shifted in both frequency and phase). I ...
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1answer
815 views

Beginner BPSK demodulation question

I'm writing a simple application in Python that sends and receives data over binary PSK using audio signal. I used cos() for 0 and -cos for 1. On the receiver side I figured I can demodulate by ...
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1answer
397 views

How does the PSK demodulator differentiates one carrier from the other in CDMA

I'm trying to understand the way in which CDMA works. Once the transmitter bit sequence is spread it is modulated for instance using a PSK modulator. Lets assume BPSK is used. I'm particularly ...
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1answer
717 views

Understanding BFSK Modulation (MATLAB/Simulink)

Could someone explain to me BFSK Modulation on the Simulink model below? The simulation above simulates a binary FSK system with a correlation (or matched filter) receiver. I have to understand the ...
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2answers
350 views

Adding a constant to a bandpass-signal in transmission

I do understand AM-DSB-SC and AM-DSB-TC, but can't see the point in adding a constant DC-offset of 2 in the upper part of this Simulink-model? Source
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1answer
193 views

Frequency-ratio at baseband IQ-mixing

I was wondering by what logic or mathematics the frequency-ration $$ \frac{f_{lo}}{f_s} $$ in the sine-functions comes into existence? Source
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2answers
576 views

Non coherent Symbol Error Rate vs Es/N0

Purpose: Implementing a noncoherent M-ASK modulation ($M=2$) and comparing the results, $\mathrm{SER}$ vs. $E_s/N_0$, to the theoretical formula. The theoretical formula is not based on differential. ...
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2answers
3k views

How to apply low-pass filter to an I/Q signal to get baseband signal?

Can anyone help me with the demodulation technique of a modulated signal? I mixed it with I/Q signal. But I am very confused about low-pass filtering. I am trying to apply a low-pass filter, but I am ...
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1answer
868 views

How to determine the symbol rate of a 2-FSK signal?

Let's say that I have a 2-FSK signal recorded so that the SNR is around 20 dB and the noise seems to be more or less white. The distance between tones is greater than the minimum distance needed for ...
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2answers
642 views

Use GNU Radio to extract information from a VOR signal

I want to design a GNU Radio project to extract the information of a VOR signal, then find the angle to the north and the Morse code of the station. Is there any example that shows how to do it?
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2answers
171 views

Decoupling two signals where one is a delayed version of the other

I have a signal $y(t)$ that consists of the sum of two signals where one is a time delayed version of the other. $ y(t) = x(t) + x(t-t_{d}) $ $x(t)$ is known but the time delay $t_d$ is not. I ...
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1answer
372 views

Downconversion / Demodulation of RF signal to DC

My question is around down conversion of a signal (e.g. RF) to DC and the affect of negative frequencies. If I have a signal whos spectral content is say between 2-4kHz and I mix this with an ...
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2answers
3k views

I/Q Sample demodulation to input data

I am trying to convert some raw unscaled I/Q sample data back to the original input data. I've been reading a lot of different posts and articles in I/Q demodulation and the focus is almost solely on ...
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3answers
1k views

Real-time BPSK demodulation

I am currently studying BPSK demodulation. Most probably my question very basic but i am having difficulties to understand the case of real-time bpsk demodulation. Basically, all the examples (matlab,...
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1answer
206 views

Pilot tone frequency doubling

U.S. Broadcast FM stereo includes a $19\textrm{ kHz}$ pilot tone that needs to be frequency doubled to help demodulate the DSB stereo difference signal. How can this frequency doubling be done ...
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1answer
463 views

Amplitude Modulation with large carrier and suppressed carrier

From what I have read so far Amplitude modulation with large carrier is favaroble because envelope detector can be used at the receiver to derive the message signal and therefore another mixer is not ...
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2answers
5k views

FSK and IQ modulation

I am having trouble understanding the FSK modulation process. There are many ways of demodulating the FSK signal. What is the advantage of performing the FSK using IQ modulation? How to demodulate ...
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2answers
2k views

Envelope detector for non-zero mean signal (Matlab)

I used hilbert transform to get an envelope signal. envelope = abs(hilbert(inputSignal)) This works for zero-mean signal: But, for nonzero-mean case, ...
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1answer
126 views

Receiving frequency modulated signal

I have two questions: If the FM radio at the receiver mixes with a another frequency to bring down the carrier frequency, wouldn't that affect the message signal? In today's digital world, why the ...
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1answer
739 views

Squaring signal for amplitude demodulation

I read the following here. Can someone explain/elaborate on this? Squaring the signal effectively demodulates the input by using itself as its own carrier wave. This means that half the energy ...
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1answer
4k views

Phase synchronization in BPSK

In BPSK for demodulation at the receiver end we do phase recovery between received wave and carrier wave. We can find the phase difference between the carrier and received waves using : PLL And ...
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90 views

Filtering and Differentiating phase-modulated signals

For a project work, I need to demodulate data from a Laser Doppler Vibrometer. The distance information is phase-modulated, therefore the velocity information is frequency-modulated: $$x \propto \...
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1answer
4k views

How to correct the phase offset for QPSK I-Q data

I have an I-Q data of QPSK modulation, the data is is smeared and I have to correct the phase offset that causes the smearing problem, how can I apply the Phased-locked loop or the Costas loop on this ...
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1answer
551 views

FSK analysis: only ever find one frequency

I've trying to write this software as part of my amateur radio and SDR hobby for analyzing various two-level FSK signals. I'm very new to DSP but have been having a lot of fun so far learning more ...
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1answer
245 views

How to find a know signal in another signal which contains other signals along with the signal i need in python

I am working on BPSK with sound waves a carrier waves. Actually I am modulating my data with some known sync bits along with the information I need to send. So the things I will be having at ...
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1answer
372 views

Demodulating upper sideband (USB) signals

A modulating signal $m(t)= \sin(2 \pi \nu_m t)$ is transmitted via a carrier of frequency $\nu_c$ using upper sideband (USB) modulation. Show that the USB modulated signal can be demodulated using a ...
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1answer
262 views

why does the decision boundary change in BPSK? is it true?

I am working on modulation and demodulation of BPSK using python. i made a code for modulation and demodulation,while demodulate i tried to compare my actual data bit stream with demodulated bit ...