# 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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### What can be done with I/Q data which would otherwise be impossible?

As I understand it, I/Q data is the complex representation of any waveform. It enables us to understand two things at any arbitrary point in time: The projected amplitude of the waveform. The ...
38 views

### Modulate Bipolar(?) signal

I want to modulate this signal if possible with an Arduino, but have no idea what circuit can help me here. Let's ignore the timing and the measurements from the image for a moment, my problem is more ...
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### Why can so little digital information be stored on a cassette tape?

I had heard that tape is still the best medium for storing large amounts of data. So I figured I can store a relatively large amount of data on a cassette tape. I was thinking of a little project to ...
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### Why is a bandpass filtered analog PM signal still PM and not AM

I know, that in theory a sinusoidally phase modulated (PM) signal with an expression like $\Re(e^{\mathrm{j}k\sin(\omega_s t)} \cdot e^{\mathrm{j}\omega_ct})$ with the signal frequency $\omega_s$, the ...
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### what is OQAM (Offset QAM) and why it is required?

Currently I am studying about a modulation technique FBMC (Filter Bank Multicarrier) which is a predecessor of OFDM. The difference with OFDM is that, FBMC does not have a CP (Cyclic Prefix) which is ...
48 views

### Can the intelligence message of an FM signal be cross-modulated to another center frequency due to non-linearities?

Can the intelligence message of an FM signal be cross-modulated to a a different frequency by non-linearities, but with the FM modulating message remaining (relatively) intact on the new frequency? ...
39 views

### Cosine modulated impulse response

How do we show $y_0(n) = y_1(n)$ when $h_k[n] = h[n] \cos(\frac{2\pi}{L} k n )$
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### Use of pulse shaping in digital modulation

Sorry, I am a little bit confused here cause I thought when we say QPSK, the signal looks like the following. I thought the bits to send/receive depends on the phase shift of the carrier, or is the ...
73 views

### QAM Amplitude Levels

I'm working on a project to stream video between 2fpgas by using QAM. While mapping symbols with different amplitude pulses(PAM) a question popped up in my mind. In real life how does communicating ...
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### How to encode binary sequence if the number of bits are odd to e.g. 4-PAM? (Beginner)

I'm new to signal constellation and trying to understand how M-PAM works. If there is a binary sequence that has on odd number of bits and I want to send a 4-PAM signal, there will be one bit left ...
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### OFDM Modulation: what's the output of the FFT?

I'm trying to understand how OFDM is used in technologies like Wi-Fi. On the Wikipedia page, an idealized transmitter is presented with this schema: Data is converted from serial to parallel, mapped ...
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### Digitalization of a signal

Suppose I have an analog signal I want to transmit. After sampling and quantization, I can map the samples to bits. So now I have a bit stream that represents the original analog signal. My questions ...
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### How to deal with modulator jitter?

I have a question regarding an implementation of a modulator. I guess some people here have an FPGA background. I would like to implement a QPSK modulator of  31 Mbit bitrate using a 125 MHz clock. I ...
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### A communication system

I am solving the following problem as an exercise. I have a signal $$z(t) = x(t)\cos(wt) + y(t)\cos(ut)$$ and we assume $x,y$ to be band-limited continuous time signals. In the frequency domain we ...
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### Use of I/Q representation for unmodulated Rx Signal

it may be a stupid question but while learning about DSP and Modulation I was wondering, if the I/Q representation of an RF Signal is of any use, when the received signal does not contain any ...
38 views

### Max frequency of cosine in SDR

I would like to transmit a 56 MHz real cosine and receive it using SDR with max complex sample rate equals 61.44MSPS and an analog filter with BW = 56MHz (the transceiver is AD9361). Can I do it? How ...
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### Why does my digital upconversion result in two tones?

I am using Xilinx's RFSoC in I/Q mode. The important point is that in the digital space I have real and complex samples. I take the incoming data and multiply it by a complex sinusoid. In my test ...
22 views

### How do you determine the power required for a phase shift keying modulation scheme?

This wiki article has a diagram : which shows how the message "11000110" is conveyed as a waveform. I'm trying to understand how the power to transmit this message can be determined. Do I need ...
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### Please, help me interpret my Simulink simulation of AM. Why does carrier not appear in the spectogram?

Carrier is 2 * pi * 25, modulating signal is 2 * pi, all the amplitudes are 1s and zero phase. I realized that I could add a sine wave right at the end. I get a carrier in frequency domain, but my ...
59 views

### I/Q Signal Power Calculation

I am trying to understand the basics of IQ modulation. The amplitude of a demodulated IQ signal is given as $\sqrt{I^2 + Q^2}$ which is easy to understand from the phasor diagram. Yet, I don't ...
45 views

### Serial to Parallel Converter

in many texts about modulators I have seen there is a component called "Serial to Parallel Converter". For instance, let's consider this scheme and let's focus on the second block (reference): The ...
45 views

### Confusion about collection of bits and symbols

I'm taking an intro communications module and I'm quite confused on what the term "symbol" really means? Consider this setup: My understanding is as folllows After the information source, we have ...