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Questions tagged [demodulation]

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

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How to demodulate Binary Offset Carrier Signal?

I need to modulate and demodulate a BOC (Binary Offset Carrier) modulated signal. I tried starting with: ...
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BPSK modulation with Eb/N0 computation

Good Morning to everyone. My goal is to create a BPSK modulated signal starting from Eb/N0. The signal is composed by I-Q components both modulated using BPSK and pulse shaped with squared-root raised ...
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Are there modulation schemes that use more bandwith than they need to, but don't require a spread-spectrum code to decode? (besides AM)

In this answer to Have deep-space spacecraft always used some form of spread-spectrum for data downlink? space scientist Mark Adler explains that while spread-spectrum proper (using specific codes in ...
uhoh's user avatar
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How can a costas loop work when root raised cosine filter used on QPSK signal?

I just finished a costas loop for QPSK signal,I transmit the baseband signal and sent it into the costas loop, which worked well, but when I filter the baseband signal with root raised cosine filter ...
sloth_shelf's user avatar
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What is the most used signal for basic pulse?

My professor said that: in order to avoid interferences/harmonics caused by the nature of the square wave g(t) (sinc will have these secondary lobes), it's better to change the basic pulse g(t) to ...
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Why don't two multiplication of the same cosine wave let me come back to the original baseband signal but instead shifts it further?

I'm trying to do a simple modulation and demodulation of a digital/binary source. I'm multiplying it by a 1khz cosine to center it at 1khz instead of 0. Then, to demodulate, I multiply again with the ...
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Frequency Modulation - Demodulation - Distorted frequency shape

I am interested in the effect frequency modulation has on the signal. I am using an acousto-optic deflector to steer a laser beam. The deflector receives a Radio-frequency (RF) signal (~100 MHz, sine-...
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CDMA using BPSK - Demodulation

I am very much a rookie, so apologies for the terrible knowledge or misconceptions. I'm looking at this mostly in the context of GPS (or sending a signal with a very low SNR ratio). I understand BPSK ...
Nathaniel Girdler's user avatar
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Why do I find a low frequency oscillation when I add a carrier frequency to my baseband signal ? And Why is my demodulation step not working?

I am trying to build a simulation for a 2PPM signal, modulate it at high frequency and then retrieve my baseband signal. Here is my full code (minus the plots) before explaining more. ...
Aloys Reant's user avatar
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2 answers
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Matched filter reference signal

The matched filter is an optimal filter that maximizes the Signal-to-Noise Ratio (SNR) to minimize the probability of error on a received signal. It is based on convolving the received signal with a ...
Mouh Kramo's user avatar
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1 answer
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Relation of SNR and BER

I am working towards establishing the error rate of the communication system relying on on-off keying. I have trouble understanding the estimation of bit error rate (BER) performance when the ...
Humphrey Appleby's user avatar
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How to demodulate a bit sequence that is offset-modulated with a complex exponential?

I have a discrete-time complex exponential $a[n]*(\cos(\omega*n/N) + j \sin(\omega*n/N)) + b[n]$ where $a$ is constant and $b$: $\{0,1\}$ So it is basically an offset-modulated sequence of bits and I ...
neolith's user avatar
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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 ...
Kuba Lhotský's user avatar
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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 ...
matt's user avatar
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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 ...
kecbackbencher's user avatar
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2 answers
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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 ...
dsp_curious's user avatar
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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 ...
Jordan's user avatar
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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 ...
Piratemetaldrinkingcrew's user avatar
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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. ...
Yudop's user avatar
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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, ...
Antonio Fernandez's user avatar
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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 ...
Jefferson Henrique C. Soares's user avatar
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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 ...
xyzabc123's user avatar
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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 ...
Ice Cool's user avatar
1 vote
1 answer
155 views

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) ...
Chris's user avatar
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1 vote
1 answer
174 views

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 ...
Villere_DSP's user avatar
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2 answers
707 views

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 ...
Levi's user avatar
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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(\...
unique's user avatar
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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 ...
Tim's user avatar
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2 votes
1 answer
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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. ...
squeakyclean's user avatar
2 votes
0 answers
69 views

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....
T.C.'s user avatar
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2 answers
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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 ...
Rubem Pacelli's user avatar
9 votes
3 answers
3k views

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 ...
juhist's user avatar
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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 ...
jcabeza's user avatar
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1 answer
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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,...
digitalman's user avatar
1 vote
1 answer
1k views

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 ...
Nick Elias's user avatar
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1 answer
244 views

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 ...
dsp_curious's user avatar
1 vote
3 answers
151 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 ...
Chris Akridge's user avatar
0 votes
2 answers
629 views

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 ...
Hubert S. Cumberdale's user avatar
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1 answer
595 views

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 ...
fjsdlkfj's user avatar
1 vote
1 answer
112 views

Why a demodulated signal can appear at a double frequency?

Why during demodulation, the demodulated signal might double its frequency? A minimal example: ...
Gideon Genadi Kogan's user avatar
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1 answer
204 views

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 ...
Borsuk Idzie Po Ziomki's user avatar
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0 answers
132 views

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 ...
Riccardo Barbo's user avatar
0 votes
1 answer
64 views

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 ...
Stephen D.'s user avatar
1 vote
2 answers
1k views

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 ...
Alexis Evelyn's user avatar
1 vote
1 answer
568 views

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 ...
Pawel's user avatar
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3 votes
2 answers
278 views

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 ...
foreverska's user avatar
-1 votes
1 answer
218 views

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 ...
piratepete's user avatar

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