# Questions tagged [modulation]

Modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with the amplitude of low-frequence modulating signal which typically contains information to be transmitted.

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### OQPSK - GNU Radio Companion

I was wondering if anyone has had any success in implementing OQPSK in gnuradio. I have a working theory of expanding on the Constellation Modulator to include a custom OQPSK function. I have ...
593 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 ...
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### Preparing data for modulation classification based on RML2016

I would like to validate a trained model based on RML2016.10a. My idea is to capture a certain amount of data (20 Msps) for approximately 0.3 seconds. Then, I identify all the signals in this ...
429 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....
1 vote
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### What is the relationship between Symbol Duration and Sampling Frequency in a 256 MPSK radio link

I'm struggling to work out the relationship between Symbol Duration and Sampling Frequency in an MPSK link. For instance, if the Sampling Frequency is 10MHz this means that a sample is taken every ...
348 views

### QAM modulation problem with python

I have a IQ signal with a bandwidth of $200\,\text{MHz}$. I do I*cos(2*pi*1000e6*t)-Q*sin(2*pi*1000e6*t), but my signal doesn't shift to carrier frequency ...
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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 ...
67 views

### Modeling an OFDM signal and comparing it with QPSK

I am trying to model an OFDM signal based on original QPSK stream and compare their baseband spectrums. I've used this article as a reference for plotting spectrum and this as a MATLAB OFDM reference ...
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### Block Diagram 2nd Butterworth Low-pass

I would like to represent a second-order butterworth low-pass filter in a block diagram, how can I get started? As per the attached image
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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 ...
27 views

### Modulating and transmitting three different voice signals (in MATLAB)

I want to record, modulate and transmit three different voice signals. I will be doing this in MATLAB. Please can you help me figure out how can I do this? Or give me a block diagram that can show ...
654 views

### 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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### OFDM does not work with USRP

I found the ofdm flowchart in the Gnu radio examples.(ofdm_loopback) Scheme: The spectrum and the received data of the received signal: After that, I connect the USRP Sink and the USRP Source. The ...
115 views

### 8PSK modulation does not work

I implemented a data transfer system using two tutorials: Guided Tutorial PSK Demodulation and Packet Communications. After that, I decided to change QPSK to 8PSK. My scheme: Constellation Sink: For ...
1 vote
124 views

### Can frequency multiplier (e.g. doubler) impact signal bandwidth?

My understanding is that if a single tone at frequency F is inputted to the frequency doubler, one should observe at its output in the spectrum the same tone but now at a frequency 2F. However, what ...