Questions tagged [demodulation]

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

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Demodulate qpsk with gnu radio

I'm trying to demodulate a qpsk signal with gnu radio. The signal is from the meteor satellite on 137MHz https://www.sigidwiki.com/wiki/Low_Rate_Picture_Transmission_(LRPT). I recorded the signal with ...
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Why a demodulated signal can appear at a double frequency?

Why during demodulation, the demodulated signal might double its frequency? A minimal example: ...
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Block diagram of a demodulator with a low-pass filter

I am having some difficulty designing a block diagram of a demodulator with a low pass filter - I don't know how to add it to the schematic(apply the LP filter to the diagram). I have an input signal ...
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Difference between MSK and CPSK

I'm trying to understand the differences between the MSK and CPSK transmission, but I am not understanding some things about it. I understood that they are two signals without discontinuity, but what ...
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Writing an OFDM modem - subcarriers are interferring

I am trying to write an OFDM modem. I've already written a QAM modem, which I'm using as a basis for this project. The way I'm doing this currently is by spinning up several QAM modulators, each with ...
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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 ...
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16-QAM demodulation

I wonder how higher order QAM modulations (like 16-QAM) are demodulated in practice. Let us assume hard detection for simplicity. For 4-QAM, checking sign of real and imaginary parts is enough, but in ...
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Is IQ demodulation through sampling offset posible

These topics are full of words I don't fully understand. So it's very possible I missed the point somewhere but I saw a feature on a microcontroller and wondered if it was applicable. I have an ADC ...
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Demodulation of amplitude data in python

I'm trying to work out a way to demodulate series of amplitude data points in python. The original data consisted of a total of 360 bits which is now contained in slightly under 720 samples (the ...
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I'm missing something when it comes to understanding FM

I understand why FM is preferred for music: noise is mostly amplitude modulated, FM yields much higher fidelity. I also understand why commercial FM signals have a much larger bandwidth than ...
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Cyclic spectrum equality to spectral correlation density

As long as I know, the cyclic auto-correlation is defined as: $$R_x^\alpha\left(\tau\right)=\lim_{\Delta t\rightarrow\infty}\frac{1}{\Delta t}\int_{-\Delta t/2}^{\Delta t/2}x\left(t-\frac{\tau}{2}\...
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Is it possible to obtain a complex lowpass signal directly from its equivalent bandpass signal?

Given the complex lowpass signal $x_l(t)$, its real bandpass equivalent signal with center frequency $f_c$ is \begin{align} x_b(t) &= \text{Re}\{x_l(t) \cdot e^{j2\pi f_c t}\} \\ &= \frac{1}{2}...
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GNURadio GFSK demod missing data

we are trying to develop a flowgraph for cubesat operation. Our flowgraph for includes both downlink and uplink parts in one flowgraph. It uses SoapySDR as a driver of an SDR. Most of the used blocks ...
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How is IQ-modulation done on the digital side rather than the analog side?

The original way of doing In-phase Quadrature (IQ) modulation is by modulating and mixing on the analog side. I have read that as the digital processing have gotten better, the modulation and mixing ...
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Why does my output signal look like this?

This is a coherent demodulation of a BPSK signal. I'm using this link as a reference However my demodulated output comes out with too many redundant values compared to the transmitter. This only ...
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What is the maximum rate of a coherent demodulator implemented in a PC?

I would like to implement my own xPSK coherent demodulator on a traditional PC connected to an acquisition board. I am wondering what kind of bitrate it is possible to reach processing only with the ...
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Digital Selective Calling (DSC) Decoder in GNU Radio

I’m attempting to develop a GNU Radio FSK decoder for Digital Selective Calling on marine VHF but I seem to be stuck. I got my hands on a Standard Horizon handheld marine VHF unit with DSC capability ...
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weird Demodulated BPSK waveform

I am using an acoustic wave of 3khz(audio BPSK) as my carrier frequency with a sampling rate of 10k samples per bit. at the receiver end, I play the audio from my phone to my computer, record it ...
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synthesizing a signal from inphase and quad components

I have a newbie question: Let's say I have a signal (fc = 308 kHz, B= 30 kHz) as plotted below I demodulate the signal to derive I and Q components at evenly-distributed time steps as (only the first ...
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Best choice to digitally rotate reference for an IQ filter?

I have analog GHz signal modulated with 60KHz signal and I analog mix it with reference GHz and low pass filter so now I have a 60KHz signal $a$ which I enthusiastically sample (at 1MHz). Meanwhile I ...
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Real-time FM demod results in clicking and strangely-shaped output

hardware engineer here dipping his toes into software DSP and running into some issues. I'm attempting to demodulate in realtime a simple narrowband FM signal with samples from an RTL-SDR, and play ...
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How to demodulate PM with signal faster than carrier?

I have a signal that is a periodic concatenation of truncated Lorentzians ($\frac{1}{1+x^2}$), like so: The exact shape of the signal is unimportant I guess. I can approximate it with its first few ...
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FM demodulation using complex differentiation

I'm trying to implement the complex differentiation discriminator which is taken from Software-Defined Radio Using MATLAB, Simulink, and the RTL-SDR. The final result is $$s(t) = \frac{s_q'(t) s_i(t) -...
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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 ...
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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 ...
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Cut-off frequency for Low-pass filters in Arctangent Demodulation

According to literature, the arctan-demodulation method commonly used in Radio-frequency radar systems is the one shown below: Is there a rule of thumb regarding the cut-off frequency of these Low-...
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Clock Recovery with FSK Demodulation in GNU radio

I'm working on demodulating an fsk signal sent from a cubesat on the ground to an antenna station. I'm trying to do it in GNU radio but I am not quite getting the original signal back. The cubesat ...
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Soft bits in large constellations

I am working on a soft iterative receiver for an M-ary modulation. Since my constellations, M=2⁷ — M=2¹², are rather big, the log likelihood ratios also become large. Is there a way to compress these ...
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Software implementation of Gardner Loop

My objective is to create a Gardner loop to remove the timing offset present in my signal. To achieve best timing SNR, I downsample my signal to 2 samples per symbol. It is depicted below: where blue ...
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RRC filter in receiver side well applied?

I would like to ask question bout the rrc filter that I applied as an matched filter for receiver side in communication. My aim after RRC filter is to draw the eye diagram, and so far the eye opening ...
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The timing offset remains after Gardner loop

I would like to use Gardner loop to remove the timing offset in order to demodulate the signal. My signal contains the frequency offset, however I know that the Gardner loop can handle substantial ...
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Symbol timing recovery in Python

My objective is to demodulate QPSK signal. At the receiver I apply RRC filter and interpolate the signal to get the values of the signal (approximately) at the sampling instances. Then I am concerned ...
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How to perform a phase recovery for higher order modulation schemes

My objective is to demodulate the signals with different modulation orders and schemes. In particular, I want to recover the phase first. Let us say, my signal looks like in the constellation below . ...
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Sampling and Demodulation question

if I have an analog modulated signal with a DSBSC modulation (modulation index 100%) as an input in my receiver and I want to convert it to a sampled signal, do I need to demodulate the signal (with ...
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bpsk demodulation only with STM32

for an internship I have to create a communication between 2 devices at 30Khz. we choose a BPSK modulation. I create du Tx with a stm32 and a DDS (AD9834). Now I trying to code the demodulation with a ...
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SDR : IQ GMSK signal demodulation

I'm trying to develop an application for the demodulation of some GMSK signals transmitted over the air. I'm using a RTL-SDR which outputs 8 bits IQ samples of the baseband signal. Here is what I've ...
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LPF in the stage of IQ demodulator is it a analgor filter or digital filter?

I recently designed the LPF of the IQ demodulator using the Butterworth LPF refering to https://dspillustrations.com/pages/posts/misc/baseband-up-and-downconversion-and-iq-modulation.html. But I have ...
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Demodulating signal by passing incoming carrier wave through low pass filter as opposed to multiplying by carrier wave?

Demodulation through many resources found online says that the incoming signal is multiplied by the carrier wave and then passed through a low pass filter that removes the carrier wave from the ...
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QPSK sync sequence detection problem

I have IQ data collected This is the beginning of the packet that includes preamble and sync sequence. Red is real part, blue is imaginary. Also constellation diagram for this data I don't have ...
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QPSK demodulator on GNURadio continuously loses phase lock

I am designing a QPSK demodulator to be used for receiving Meteor M2 (LEO satellite) signals (QPSK at 72Kbaud). However, I am finding a lot of problems in my way. First of all, this is the flowchart I ...
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Demodulating unknown signals - unmatched frequency sampling

My goal is to make an approach to recognize modulation type of unknown signals. I have energy detector which monitors spectrum and it provides information about center frequency and bandwidth of ...
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Block diagram of M-PSK modulation and demodulation

I have come across this quadrature modulator block diagram in many books and websites: I've read that the quadrature modulator allows to realize many different digital modulations, including ...
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Most efficient way to find single dominant frequency (without amplitude) in analog signal

I want to construct a reference locked sine oscillator. The multibit sine wave is calculated using DDS. The multibit reference signal is typically not sinusoidal, can have offset and substantial noise,...
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Why in FSK the phase shift is allowed?

FSK modulation encodes information into the frequency of the signals. But when I checked the reference books, the formal expression for a frequency modulated signal is: $x_i(t) = \alpha cos(2\pi f_it +...
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FM modulation - recovering bits

I'm trying to complete one task: Download some FM modulated signals from page http://www.w1hkj.com/modes/index.htm. Calculate their spectrograms, i.e. short-time Fourier transform. Observe different ...
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Decoding images from NOAA satellite APT signals

I've been working on a decoder for these APT images for a while now. I started years ago, in Python, and was able to implement a working decoder quickly. A few months ago, I came back to the project ...
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Trade-off in sample-rate & FFT-size & Doppler

I've got a stream of digital IQ samples let's say at $F_s = 1 MSPS$ that consist of a narrowband signal, in awgn. Let's say the signal BW is ~ 100Hz. The narrowband signal's center (or base) frequency ...
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Dealing with bias in an FFT for frequency correction

I'm working on using an FFT for frequency correction of a generic modulation signal. My algorithm basically attempts to balance the energy in the positive and negative frequencies of the FFT to be ...
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Digital Phase Modulation baseband or passband?

Say I want to transmit messages using PSK: I send the message $$s_m(t) = \text{Re} \left [g(t) e^{\frac{j 2 \pi (m-1)}{M}}e^{j 2 \pi f_c t} \right]$$ where $f_c$ is the carrier frequency. Now my ...
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Non-coherent FSK and Orthogonality and square-law detectors

This is a basic figure that explains how Non-Coherent FSK actually works. The incoming signal $ r (t)=\sqrt{2 P}{Cos}(2 \pi t (\text{fc}+\text{fi})+\text{n(t)}$ where P denotes the signal power in ...
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