Questions tagged [demodulation]

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

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24 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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57 views

Quadrature demodulator. Relationship of sampling rate and error

Task: to estimate the frequency of the power grid signal. I use a quadrature demodulator. I get the I / Q components. I calculate the angle (phi = atan(Q / I)). I differentiate the angle and get the ...
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Auto correlation , Time duration measurement for SDR calculation purposes

I'm a SDR and DSP beginner , I'm trying to find correlation between pulses I receive using a SDR, with a replica that I have (basically pulses with predetermined duration's). I've looked in this ...
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20 views

Envelope detector for AM signals

How or what are the constraints for deciding factors of envelope detector for AM As far as I know that charging time of capacitor should be below 20T where T is periodic time of carrier and ...
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24 views

Channel state information from non-HT packets: is that possible?

I read several papers about CSI data, but one thing is not clear. I would like to extract csi from legacy rate packets. I read some forums related to existing CSI tools and they only state that CSI ...
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56 views

What is the minimum sampling rate for QPSK or what is the bandwidth of QPSK signal?

Consider we have created a QPSK signal with a carrier frequency 100kHz. Before applying matched filter or demodulation we need to take samples from the received signal. So what is the minimum ...
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82 views

Amplitude demodulation of sinusidal signal in matlab

AM-demodulation task and I was asked to demodulate the signal in MATLAB and the result should contain three pictures. plotting the $fft$ the (frequency spectrum)of the signal i was able to determine ...
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42 views

How to correct a QAM time delay

How can you correct the anticlockwise rotation that occurs in the received constellation of a QAM system? My only idea is to compensate the delay with an advance but this is impossible since you ...
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87 views

Getting the bitstream of an unknown RF signal

I am trying to get the bitstream of a signal sent over 433MHz. I have installed SDR# (I'm on Windows), connected my NESDR SMART, and I identified the signal here: I can see there is only one peak ...
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Derive the LFSR sequence from demodulated bitstream

I'm new here and hope to have good feedback from you. I'm trying to blindly demodulate an RF signal and managed to get a sequence of bits for a preamble. After some research, I'm in fact exactly in ...
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1answer
73 views

How can an SDR recover a high-frequency signal?

How can software-defined radios operate at high frequency? The Nyquist rate dictates that you need to sample at twice the frequency to fully recover the signal. If my signal of interest is modulated ...
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What determines the maximum/minimum values in I/Q constellation diagram?

I need to do some data analysis on I/Q samples and was trying to know what are the parameters that determine the maximum/minimum values of these samples. In other words, what determines the maximum/...
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IT++ and Alternatives DSP Libraries

I want to implement some signal processing blocks in C++ so I did a bit of search on the available libraries for signal processing in C++ and I found that IT++ provides comprehensive set of functions, ...
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180 views

modulate/demodulate audio file as FSK signal mixed with music signal

What I want to do: I want to encode an audio message inside a regular music file; this shall be decoded by an audio analyzer running on another machine (by listening to the audio playback from the ...
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qam demapper why are soft-outputs used?

I'm starting to learn about OFDM QAM demapping, and a lot of documentation points to using "soft-output" algorithms that calculate Log-Likelihood Ratios (LLRs). Why is this method advantageous? My ...
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233 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
478 views

ASK demodulation using DSP

I need to implement an ASK (ampliltude shift keying) demodulation using a DSP ( a dsPIC ) and programming in C. Especifically talking, I need to demodulate a signal from a car's key transponder. I ...
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Demodulating FSK audio in Python

I am trying to write a Python script that can demodulate an FSK modulated audio file and return the data encoded in the audio. The data being transmitted is GPS NMEA strings which are embedded as the ...
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1answer
384 views

How to set a Carrier Wave for DBPSK Modulators in gnuradio?

for a Project I need to build an Audio Modem in GNU Radio. I decided, that it would be the best to use DBPSK Modulation, because that is fast and relatively noise resistant. But as it seems, the ...
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Effect of down mixing on complex demodulation method

As I know, IQ demodulation (complex demodulation) consists of three steps: Down mixing X(complex demodulation)(t)=X(real signal)(t).{exp⁡[(-i2π(f_demodulation).t)]} low pass filtering decimation ...
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1answer
126 views

Bpsk demodulator implementation

For a project I'm trying to implement a BPSK demodulator on some random wave files, I'm getting a few difficulties: How do I know my bit rate, i.e. how many bits each 'real data bit' I'm having. How ...
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330 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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Term for signal waveform correction or demodulation

Let say a periodic signal waveform $v(t)$ can be modeled as: $v(t) = f(\phi) A \sin(2\pi ft + \psi)$ where $A$ is a constant amplitude, $f$ is signal frequency, $t$ is time and $\psi$ is a constant ...
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120 views

From IQ to pi/4 DQPSK

I need to decode $\frac\pi4$-DQPSK packets from an SDR, preferably in C#. I have the SDR receiver part done. Now I'm trying to learn how to take the IQ stream and get the packet info from it. I've ...
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Help in identifying low speed image transmission protocol over RF

In the seventies I worked for Muirhead on press fax machines that used to transmit pictures over radio and landline as I recall two FM systems were used a carrier 800 Hz modulated +- 150 Hz and 1900Hz ...
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Demodulation with MATLAB

I am trying to listen VLF radio signals. I have a recorded wave file (download) and here is the frequency spectrum: I have produced this spectrum using this matlab code: ...
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35 views

Signal acquisition equipment phase noise

I would like to check if there is a way to enhance an RF equipment's phase noise figure. The considered RF acquisition homodyne system includes a mixer for carrier demodulation, amplifier and filter ...
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177 views

In case of using a Doppler radar, do we have to use IQ demodulation to find the direction of a target?

I want to know the way to find the velocity of a target by using a doppler radar. I read some paper about it, In summary, send rf signal to a target receive the reflected signal from the target. ...
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3k 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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31 views

Changes in amplitude after Quadrature Demodulation

I'm getting the FSK signal from the satellite in I/Q format (see the last 2 waves at the bottom of the picture). After applying Quadrature Demodulation, I'm getting the top wave. The questions are:...
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46 views

Symbol synchronization with M-QAM. M < 16

I working on M-QAM system using a Cortex-M4 processor. Using a alternating symbol as a preamble, I am able to get carrier lock. Symbol synchronization is then achieved by finding the peak. An early ...
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1answer
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What does the phase discriminator portion of the Costas Receiver do mathematically?

What does the phase discriminator portion of the Costas Receiver do mathematically? The output of the I-channel is $ \frac{1}{2}A_C \cos \phi \, m(t) $. Which means for small deviation of phase $ \...
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How does a Costas Loop lock to one of multiple BPSK signals

I've been looking into how GPS receivers work in terms of signal processing. When a GPS receiver tracks the received signal, it often uses a Costas loop to synchronize the carrier. How that works ...
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CDMA-DSSS with orthogonal codes and BPSK modulation: proper way to demodulate

I am having problems when demodulating the signal: If I demodulate the sequence chip by chip and then operate only with binary information the "integrate and dump" (correlator) sometimes will provide ...
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1answer
211 views

dvb-s to dvb-c direct transmodulation

Is this possible to direct trans modulate DVB-S/S2 -> QI into -> DVB-C/C2 signals without doing it the way DVB-S/S2->Demodulator.ic-Transport Stream -> Modulator.ic-Transport Stream -> DVB-C/C2 ? Qpsk ...
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112 views

Demodulation in Rayleigh Flat Fading Channels

A core part of demodulation in Flat-Fading channels is (assuming) the channel as a(random) constant complex number multiplied with your signal. This is done in order to de-rotate the symbol for ...
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Filtering of an AM signal at the reciever

Transfer function of a filter at the input of a receiver (synchronous demodulator of AM signal) is given with equation: $$H(f)=e^\frac{-(f-f_0)^2}{B^2}+e^\frac{-(f+f_0)^2}{B^2}$$ $B=10kHz$ It is ...
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1answer
137 views

RF demodulation for dummies

Given a signal that's been FM encoded on a carrier wave, what are the individual steps I need to take to demodulate it, and recover the original signal? I don't have a background in signal processing,...
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2answers
119 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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3answers
79 views

Representing data in combination of QAM and BPSK

I have a question regarding the data representation in different modulations. Assuming we are using MIMO system whith $4$ $T_x$ x $4$ $R_x$ which means four transmission antennas by four receiving ...
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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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1answer
48 views

About combination between QAM and PAM

I have confused question regarding the possibility of combination between QAM modulation and PAM in order to improve the spectral efficiency. Is that possible? As you see in the below Figure, it's ...
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2answers
129 views

Why would we simulate baseband rather than passband

My question is, Why do we usually use baseband in simulation rather than passband? however, if we want to test our simulated idea in real environment, it must be sometimes in passband !! So, should ...
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129 views

How to calculate the accurate BER expression of circular 8-QAM constellation modulation?

It is easy to understand the BER derivation of square QAM, but the circular 8-QAM? I'm quite confused. The decision region is not in a rectangular shape anymore, meaning regular way does not work here....
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2answers
74 views

Contradiction between complex baseband and real-valued baseband

Suppose a direct-conversion transmitter+receiver (ideal transmitter) along with its filters. In complex baseband, the filters in the signal chain can be modeled as a complex-valued FIR filter ($y$, $c$...
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136 views

QPSK constellation from baseband signal

My IQ sampler is measuring a QPSK carrier at a set frequency/bandwidth (40MSamp/s), but shifts the signal spectrum to baseband. My signal is 1.5Msym/s, but sampling at 1.5Msym/s gives me a ...
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1answer
142 views

Quadrature demodulation, homodyne detection, lock-in detection - what's the difference?

Quadrature demodulation Homodyne detection Lock-in detection What is the difference between these terms? Are they all synonomous? In my mind they kind of are, so I'm never sure which to use. I ...
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What is the relationship between FFT size and demodulation in OFDM

As I mentioned in the title of the question, how can we demodulate the data in order to get the same number of subcarriers with different FFT size. For example, 10 MHz LTE can be sampled with 15.36 ...
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1answer
206 views

How can I do QPSK in MATLAB [closed]

Could you please explain the step below, what is the benefit of it and how does it work. . I do qpsk demodulation, do I started doing the meshgrid, ...
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2answers
3k views

How to recover complex values (downconvert) from FM modulation (composite signal)?

How does one recover the complex IQ data from the output of a FM modulator. I have combined my signals correctly and performed FM modulation on them, now I'm looking for a way to find the IQ values ...