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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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22 views

### 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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32 views

### 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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48 views

### 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 ...
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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 ...
62 views

### 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 ...
52 views

### 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. ...
1 vote
168 views

### 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 ...
1 vote
207 views

### 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 ...
83 views

### 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 ...
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1k views

### 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 ...
102 views

### 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 ...
209 views

### 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 ...
149 views

### 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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### 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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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....
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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 ...
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 ...
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1 vote
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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,...
1 vote
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 ...
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 ...
1 vote
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 ...
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 ...
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 ...
1 vote
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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 ...
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 ...
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 ...
1 vote
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 ...
1 vote
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 ...
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