Questions tagged [demodulation]
Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave.
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Help me understand the concept of IQ signals
I am a computer science student working on a school project involving RTL-SDR receivers, and I have a hard time grasping the concept of IQ data. Basically what I think I have learned from all of the ...
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How to distinguish I from Q components when receiving a signal?
Here below is the SDR for the O-QPSK demodulation for the Aqua satellite.
How are we sure that the I component we get in the Costas Loop output is not the Q component of the original signal?
Because ...
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IQ time domain data to Constellation regeneration for a OFDM 16 QAM signal at different power levels to obtain EVM vs Pout information
16 QAM OFDM signal at output of Power amplifier at fixed frequency and different input power levels are received as a IQ data (time domain) by Spectrum analyzer, I would like to generate 16 QAM ...
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Demodulation + LPF gives derivative of modulated signal
I'm new in this community and I hope it is the right place to post my question. Unfortunately, signal processing and electronics in general are not my fields, so I'm sorry if the question is trivial.
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Why for bandpass signals complex envelope and pre-envelope signal representations are used in digital communications/analog communications (FM)?
When we need to analyse band pass signals we use complex envelope and preenvelope representations, wherein a signal is given an equivalent low pass representation.
My issue is why it is done, though I ...
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How to choose sample offset values in timing synchronization for a QPSK demodulator?
I am implementing a timing synchronization loop for a QPSK demodulator. I have chosen to use a Gardner timing error detector, which has often been mentioned. I am about to close my loop and I am ...
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DS-CDMA Spreading Code Length Selection
I'm trying to wrap my head around the process of selecting DS-CDMA spreading codes, and I'm having trouble understanding the tradeoffs of longer codes. For all scenarios described below, I'm using a ...
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Understanding homework solution - why are $\{X_t\}$ and $\{Y_t\}$ joint WSS, and finding Wiener filter + error
I'm walking through the published solutions of my homework and I'm struggling interpreting them. In them I was given a random Gaussian process $\{X_t\}$ and a random variable
$$\{Y_t\} = X_t\cos(2\pi ...
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How to remove phase shift for a baseband signal given an estimated CFO (Bluetooth)
I am working with Bluetooth specification 5.1 where the advertisement packets can send a constant tone extension (CTE) over the baseband signal to estimate the angle of arrival with an antenna array.
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Using GNU Radio to perform EVM measurements
Is there any previous work describing the implementation of an Error Vector Magnitude (EVM) measurement system using GNU Radio?
The system in question is made of an SDR HW platform, e.g. USRP, ...
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TX RX text via gnuradio using hack rf
I have a problem here - either I'm stupid or my hack rf is broken
I am trying to send text via 2 hackrf like in this tutorialusing GMSK
The simulation returns the text is correct, but when I run the ...
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Which type of modulation is used in this RF Signal?
I am working on reverse-engineering a few devices, I got some using ASK and FSK but I could not grasp this other one. I am attaching some photos from its captured signal took from URH (Universal Radio ...
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Sharp spikes in unknown signal [duplicate]
I am trying to decode an unknown signal, which has those really weird spikes/jumps.
My assumption is that it is somehow (B)PSK modulated but the signal looks really odd as shown in the screenshot. The ...
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How to correctly accept Polar/LDPC encoded bits with PSK modulation?
I have implemented a packet reception and transmission scheme using QPSK. Next I decided to add Polar/LDPC encoding. As a result, nothing is written to the received file.
I think the thing is that I'm ...
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Discontinuous jumps in phases from complex demodulation
I am using complex demodulation to estimate slow amplitude
and phase changes over time of a single sinusoid. The time
series consists of continuous blocks with large gaps (~30%
of block lengths) ...
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How to implement FLL / carrier recovery? Code and math included
There are lots of options in textbooks, youtube and website blogs.
There seems to be three options:
Calculate phase difference between samples to infer frequency error or offset.
Calculate phase ...
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Converting real samples to IQ
I have real-valued samples of a signal at a negative frequency (was mixed with a cosine of a higher frequency than itself). I want to quadrature modulate it up from $-\omega_c$ to 0. There seem to be ...
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Why don't we need frequency and phase correction in AM and FM?
As far as I understand, double sideband AM with carrier and FM can be demodulated via SDR (Software Defined Radio) without frequency or phase correction. For AM, received signal is
$$r(t) = A(t)\cos(\...
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MSK without I/Q data
I just started a while ago with DSP and slowly staring to understand the concept of I/Q and what it means. I successfully could decode some bfsk, bpsk and wanted to move to msk which as not easy to ...
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Choosing the scaling parameters for a modem implementation
I have succesfully modeled a modem using floating-point data and with the following scheme, where the SRRC filter has gain G=6dB.
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Demodulating 7x Sequential BFSK Signals
I'm hoping someone could help me find a demodulation approach to an FSK signal contained in wav files that has 14 unique, and evenly spaced channels. They appear to be separated into 7 BFSK pairs. I.E....
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Practical problems in down-converting via Hilbert filter
While teaching communication system to my students, I showed different ways to define the diagram block of the system responsible for transforming a bandpass signal, $x(t) \in \mathbb{R}$, into its ...
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Can humans hear Hilbert transform in audio?
I stumbled upon Hilbert transform when researching single sideband modulation. Apparently when the demodulator frequency is bit off by $\Delta f$, the signal after demodulation and low-pass filtering ...
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Higher order M-FSK modem implementation
I am looking for the optimum modulation scheme to build a half-duplex modem minimizing the required SNR at the expense of bandwidth efficiency. The key system parameters are described below:
Target ...
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OQPSK and MSK receiver sensitivity comparison
Which wireless receiver has the better sensitivity for the same everything except the change in the Base-band de-modulation, one base-band demodulator for OQPSK and other base-band demodulator for MSK,...
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How to demodulate FM I/Q output from SDR#
Using SDR#, I saved the baseband I+jQ signal centered about a commercial FM station to a *.wav file. I want to write python code to demodulate this signal. I know that SDR# can read in that file and ...
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How to make a discriminator for a real FSK signal?
I would like to create a discriminator of an FSK signal in order to demodulate it.
I only have the real part of the signal and it is centered in zero frequency (baseband)
My main problem is that I am ...
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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 ...
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How to recover symbols from a 4-FSK signal received over the air?
I have an RTL-SDR dongle which is tuned to a carrier frequency in my area which corresponds to a P25 radio channel (506.7375MHz).
Using MATLAB's SDRRTLReceiver function, I sample the signal at 240KHz ...
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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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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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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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