Questions tagged [modulation]

Generic term for coding information onto another carrier signal

53 questions with no upvoted or accepted answers
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39 views

How to get a band-limited digital modulation of X type?

I am developing a program which should create modulated signals and combine them to get an RF signal with different modulations on different frequencies with non-interfering bandwidths. The problem ...
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1answer
39 views

Filtering a demodulated signal

I've created a simulation on Matlab of amplitude modulation. After demodulating the signal I need to add a low-pass filter to remove the high frequency components. I'm confused as to why this is? I ...
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2answers
49 views

High Frequency Laser Modulation

I am looking at doing some phase-shift lidar experimentation. To get good accuracy, all the papers suggest that I need to be modulating the laser diode sinusoidally at ~200MHZ. I am finding ...
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96 views

How might the Lecroy HVFO High Voltage Fiber Optically Isolated Probes Work Internally?

I've been looking into these fiber isolated probes that Lecroy makes (http://teledynelecroy.com/probes/probeseries.aspx?mseries=537), and I'm curious how they're sending the signal over the optical ...
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1answer
34 views

Why the intersection points in SPWM define the width of the pulse?

After my previous question Why the triangle reference wave is used in PWM for sine modulation I still have some troubles on one particular point of natural sampled PWMs or more precisly SPWM. My ...
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20 views

What is the difference between using a baseband representation of a QPSK modulation scheme and a theoretically simulated QPSK modulation scheme?

I'm looking to compare the BER vs SNR performance of a QPSK modulation scheme, one which is a theoretical simulation on MATLAB and the other is a baseband simulation on MATLAB but I'm struggling to ...
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62 views

Foster - Seeley FM Demodulator Explanation

Consider this Foster Seeley Demodulator If I have correctly understood, its basic working principle is the fact that at the secondary coils (L2) of the Balun there will be two signals equal and ...
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58 views

What effect do R5,R6,R7,R8 have on the following DSBSC Modulator?

I know that the first 741 essentially adds m(t) and c(t).The gain should be 1 so why do we have 3.9kohms resistance ? What use is it ? The second 741 circuit is a band pass filter . I think there is a ...
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1answer
57 views

Powering 4 modulated IR LEDs through transistor

I've done some research but can't seem to find an answer to my specific problem. I'm using an Arduino as a beam-break sensor. In order to do that it modulates the IR LED at 38kHz by code and listens ...
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152 views

How to do fast RF on/off keying

I'd like to make a circuit that essentially produces very brief bursts of an RF signal, for example RF at 10MHz to 200-300MHz bursts of tens to hundreds of nanoseconds. For example this could be just ...
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2answers
161 views

Is the use of a Lock In with a signal generator appropriate and practicable?

I want to generate a 5 kHz microwave pulse to induce a sample signal. This microwave pulse has an underlying microwave frequency of 2 GHz. In order to investigate very tiny signals, which should arise ...
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140 views

Showing QAM constellation diagramm on signal analyzer

I've been playing with some lab equipment recently in order to learn more about digital modulation techniques. I've connected R&S signal generator SMIQ 03B with the R&S spectrum analyzer FSIQ ...
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349 views

How to make QAM (quadrature amplitude modulation) of a square or sinc wave signal?

I found this discussion of QAM in a communications text book and internet. "...load it into Matlab using imread(), which will give you an array of ...
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83 views

Isolation Amplifier Design Issue

I modulate input signal with triangle wave to create PWM signal. When I am creating triangle wave I use astable multivibrator and integrating circuit. unfortunately there are offset at my triangle ...
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68 views

Compressed single-sideband modulation?

I've had an idea for a new form of SSB modulation, using half-angle formulas as a basis for compressing the sideband of a SSB voice transmission. However, this idea seems so simple that I feel it must ...
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126 views

Speaker designed for ultrasound operation

I've created a transmission protocol in order to transmit information bits between a PC speaker and a smartphone, or between 2 smartphones using ultrasounds. I've implemented a QFSK system which uses ...
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604 views

Amplitude modulator for a sine wave generator

I have a home made, mostly using the design in a magazine article, radio frequency signal generator, and I would like to be able to modulate (AM) the sine wave output, which is up to 8 MHz, with an ...
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1answer
24 views

What does 'succeeds' and 'precedes' symbols mean in design of a peak detector circuit?

I am looking into the design of a peak detector circuit for demodulating an amplitude modulated wave. The circuit is a diode 'detector' connected to a low-pass RC filter. I have been given the ...
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1answer
33 views

Coherent and non-coherent detection

Let's say I am simulating something as simple as BFSK. It has two symbols, one entirely on the real plane, and one entirely on the complex plane for representing let's say zero. That is how the ...
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20 views

Is \$ H\left\{x_h(t)\right\} = H\left\{x\left(t-\frac{\pi}{2w_c}\right)\right\} \$ where \$H\$ is Hilbert transform

Accordind to my understanding of the following: $$H\left\{X(f)\right\} = -j\;sgn(f)\; X(f) \qquad(1)$$ my work so far: since \$ x_h(t) = x\left(t-\frac{\pi}{2w_c}\right)\$, Their Hilbert ...
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48 views

FM Detector Using LM565

I am currently working on a power line communication project. I want to send an audio signal through the power line. In order to do that I would need to modulate my signal and in this project I am ...
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31 views

Transmitting .mp4,.bin,.txt files with on off keying OOK (optical communication)

How do you implement OOK to transmit mp4 files etc. For instance i have LED and a video file to transmit. How do you take the video convert it to binary, send it via the LED recieve it via the ...
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25 views

How can I remove the return paths for a series of circuits and still know when they are completed? NFC/RFID? Multiplexing? Goubau line?

Apologies for the vague title. And know that my electronics knowledge is rather limited. Also my circuit diagrams may be incorrect. I currently have something like this, which represents contacts on ...
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42 views

Zero - IF receiver main limits

I was reading these slides about receivers architectures, and I have some questions about Zero - IF receivers: Precisely: Why is the spectrum around the carrier (i.e. the 2 "side bands") mirrored ...
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21 views

8-psk modulator design using any method

I want to build a 8-Psk modulator, I have searched the Internet but out of answers for a more simplified circuit.... I am open to any approach including arduino
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38 views

How can I know which constellation diagram has a lower symbol error just by looking?

So for the following example: How would I know which is less prone to error? $$C1=[−3−3j,−3+j,1−3j,1+j,−1−j,−1+3j,3−j,3+3j]$$ $$C2=[−3\sqrt2j,−2\sqrt2−\sqrt2j,2\sqrt2−\sqrt2j,\sqrt2j,−\sqrt2j,−2\...
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34 views

Phase and constellation diagram

I have noticed that when, for example, \$cos(t)\$ is in-phase (I) component of the modulated signal, we can determine the phase from the constellation diagram measured counterclockwise from the ...
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16 views

LA72910V Demodulator and Modulator Noise Problem

The project includes a DC power supply that supplies two cards and provides a network. The video signal is modulated through LA72910V whether a card is demodulated in the other card. There is no ...
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34 views

Setting up parameters for generating QAM signals

I am trying to simulate multiple baseband QAM signals for random data at varying power levels, data-rate, carrier frequency, and modulation order using MATLAB. Here is how I set up the parameters: <...
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30 views

How to perform multiplication at the time series level for chirp signals

As the title said: How to perform multiplication at the time series level for chirp signals? In LoRa modulation, when received a chirp modulated signal, to demodulate it, LoRa will first multiple the ...
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1answer
49 views

Convering bandwidth (frequency) to bit rate without knowledge of the modulation?

How would i convert a bandwidth of say 30kHz to bps if I only know the number of bits per sample (4)? (and I was using a two chanel system). I am assuming it is simply 30KHz * 2 * 4 but this may be ...
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32 views

Bessel function normalization graph

This graph is drawn bessel function table but ı stick around reading table.Does table gives directly frequency spectrum amplitude values or only jn(ß) values?
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52 views

Three level PWM modulator circuit feedback simulation

I'm trying to design a three level PWM circuit with feedback and i'm struggling to understand the feedback aspect. The design is based on this design by Texas instruments and modified to suit three ...
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1answer
21 views

Conversion Gain Definition for DSB-SC Upconversion

If I multiply a baseband signal \$A cos(C\omega t)\$ and a carrier signal \$B cos(D\omega t)\$, the result is \$\frac{AB}{2} [cos(C-D)\omega t+cos(C+D)\omega t]\$, which is a double sideband, ...
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290 views

Amplitude modulation with diode

I was studying about amplitude modulation and I found this circuit on the internet. Does anyone know why that ground is needed? Is the first part(three resistors) an adding circuit? Does the diode ...
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46 views

Modulation index and sidebands

I have built a Mach Zehnder interferometer in which a laser beam is first split. After each splitted beam is passed through a AOM driven at a fixed RF in my case 40 MHz and 40.04 MHz they are ...
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1answer
94 views

Delta Modulation Frequency in the Integrator

Ok guys, I can't understand a thing, I have made this circuit, that is a delta modulator: As you can see with an input of 5Vpp, in the output of the integrator I found a square wave signal, that has ...
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1answer
250 views

Build an FSK modulator using the HB100's transmitting signal

I want to use the HB100 to make an FSK modulation on a microwave signal. The reason why I use HB100 is that in this way the RF circuit is ready. I thought about doing an FSK modulator like the scheme ...
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185 views

Coherent FSK Modulation correlation coefficient derivation

FSK has a large bandwidth requirement and its minimum bandwidth is around \$4 B_T\$, where \$ B_T \$ is the bit rate. In a coherent FSK system the signals \$s_1(t)\$ and \$s_2(t)\$ representing bit ...
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1answer
168 views

Is this figure a correct (O)QPSK waveform?

I am currently reading Pasupathy, Subbarayan. "Minimum shift keying: A spectrally efficient modulation." IEEE Communications Magazine 17.4 (1979): 14-22. The paper explains MSK as a form of OQPSK ...
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2answers
67 views

Interference between signals having OFDM and DSSS modulations

If there are two signals, one having OFDM modulation and other one having DSSS modulation occupying the same bandwidth and over the same part of spectrum, will i be able to demodulate both signals ...
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489 views

Phase Modulator with JFET

At the university we have seen this circuit as a Phase Modulator: simulate this circuit – Schematic created using CircuitLab where \$m(t)\$ is the message at audio frequency and \$v_p(t)\$ is ...
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2answers
47 views

OFDM demodulation time

How much time does it take to demodulate one OFDM symbol? In 802.11a standard the Symbol Interval Time is 4us. Does this mean that each symbol is demodulated within this period or there is pipelining ...
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114 views

Output of a PSD fed a square wave

This is the question given in one of my papers. Input is a square wave, if phase shift was zero it would be just flat positive line, if phase is pi it would be flat negative line. Here the phase ...
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1answer
513 views

Is it true that frequency deviation over 2*pi is the phase deviation of an FM/PM signal?

for ∆f frequency deviation if for FM only and PM has Phase deviation. and Kf= ∆f (Hz) of FM? Kf = ∆f (rad/s) for PM? and for th rules: ∆f=(kfmp)/(2p) for FM where mp = mp max-mp min ∆f=(kfmp)/(2p) ...
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271 views

Delta modulation (DM) signals

Trying to understand this circuit. Will this produce a representation similar to example in second image (if U_inf is the sine wave "original") ? Assuming that, I expect U_DM to look like the "...
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1answer
65 views

PAM nonlinear amplitude compression in lower eyes

I needed some help to understand why at Rx, we observe different effective SNRs in individual eyes for higher level PAM signalling. If you need additional info, http://literature.cdn.keysight.com/...
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400 views

QAM Modulation Frequency vs Carrier Frequency

In QAM (Quadrature Amplitude Modulation) theory what is the relationship between the modulation frequency and the carrier frequency called? It is often stated in QAM tutorials that the carrier ...
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136 views

optical wireless link short range high throughput

I am student and I want to realize a wireless optical link in order to have a throughput of 100Mbps max and the distance between the emitter and the receiver is about few centimeters. I have made my ...
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2answers
81 views

Relation between the Fourier transform of Y and X

So, I watched a video from MIT Signals and Systems Open course on youtube, and there is a moment when he substitutes \$ x(t)e^{jw_ct} \$ for y(t), and then: Shouldn't it be just \$ X(w - w_c) \$ ? ...