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Questions tagged [modulation]

Generic term for coding information onto another carrier signal

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Single Ended DAC to Differential Input Modulator

I'm trying to drive a differential input IQ modulator (LT5571) with a single ended DAC (MCP4912) for modulation of a narrow band signal (~10kHz max). Because of the nature of the low frequency ...
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29 views

Source generator for Satellite Tuner input

I need to design a source generator for a TV factory. They want to automatize the functional tests by applying a test module to the TV's at the end of the production line. All the peripherals of the ...
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35 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
17 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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Understanding Hilbert Tranform in SSB modulation for AM

I am studying about Hilbert Tranform in SSB modulation for AM When I read about matlab docs on hilbert transform , why "a signal's negative frequencies are phase-advanced by 90 degrees and the ...
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1answer
48 views

understanding AFSK and FSK

I’d like to understand 1200Hz/2200Hz AFSK in commonly used APRS/Packet/AX.25 applications. When I look at the datasheets for some of the chips existing projects use (e.g the Si446x transceiver-on-a-...
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25 views

Labview - Active amplifier

I need to create a pulsed current variable from 0 to 20A to run solenoid with a very low resistance. Which is the best solution for you? Right now I am trying to generate a pulsed current with ...
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2answers
76 views

Why don't we use analog remote mics?

All remote microphones sends digital samples over the ether. Why no analog remote microphones? I know that digital signals are less sensitive to noises, but there are several advantages of analog ...
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50 views

iPhone headphone out as a signal source for AM modulation circuit

EDIT: I wonder what is the appropriate model for an iPhone/MP3 player audio out? I imagined it as a voltage source that would support whatever current the resistance it’s connected to necessitates. Is ...
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2answers
55 views

What does the phase discriminator portion of the Costas Receiver do mathematically?

What does the phase discriminator portion of the Costas Receiver do mathematically? The output of the I-channel is \$ \frac{1}{2}A_C \cos \phi m(t) \$. Which means for small deviation of phase \$ \...
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1answer
33 views

Does DSB-SC signals retain original shape of the message signal \$ x(t) \$ when \$ x(t) <0 \$?

The conventional DSB-FC AM signal is given by: \$ s(t)=[A+x(t)]\cos \omega _C t \$ In conventional DSB-FC AM we take care of the fact that \$ |x(t) | <A\$. So that the modulated signal is not ...
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How is companding different from pre-emphasis and de-emphasis?

What I know is that interference increases linearly with frequency and thus noise power is concentrated at higher frequency. So, to reduce noise, pre-emphasis and de-emphasis filters are used which ...
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103 views

How is the power of a SSB-SC signal half that of DSB-SC signal?

Intuitively I get it that my SSB power has to be half of DSB power but mathematically I am unable to get this. Say working for tone modulation. $$m(t)=mA\cos(w_mt)$$ where m is modulation index. ...
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72 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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2answers
94 views

Why different SFs in LoRa are said to be orthogonal?

As orthogonality is an important characteristic in LoRaWAN but most public references just make a conclusion that different SFs are orthogonal. This confused me a lot and hope to make a clear ...
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1answer
41 views

How come optical data modulation is faster than that of electrical modulation while optical modulation is done by electricity?

why optical data is of high bandwidth that that of electrical copper data bandwidth when we use electrical signal to achieve optical data modulation ?
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31 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
52 views

Quadrature modulation Digital to Analog

I want to use an FPGA to generate quadrature modulated signals for use with an RF transceiver (something like MAX2828 ). I am confused specifically about how the digital to analog modulation should ...
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2answers
40 views

Finding required BW with Bessel table

The FM signal (see image 1) is applied to a 50 Ohms antenna, and I am seeking the required bandwith with the Bessel table (image 2). From the FM signal, I deduced that the information frequency is ...
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1answer
100 views

FM Transmitter (Modulator) Circuit Simulation Problem [duplicate]

I've asked my question before, and I am writing this new question with some edits based on my previous problem. I am building a small FM Modulator ( Transmitting ) simulation on (Multisim). I've used ...
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1answer
188 views

FM Transmitter Circuit (range 3 km) on Multisim

I am new to the telecom simulations system specially multisim, which I am having a project that I want to simulate. My project in (Analog Communications) is consisting to have FM Transmitter (...
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1answer
33 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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2answers
352 views

What's the name of signal encoding used by WS2812 LEDs? [duplicate]

The WS2812b color LED uses some kind of duty cycle encoding to encode three states: one zero reset This can be seen in the following figure: (Source: https://cpldcpu.files.wordpress.com/2014/01/...
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1answer
118 views

How to understand this simple voice-over-laser circuit

The Sci-Toys project A simple laser communicator shows a surprisingly simple way to send an audio signal over a laser pointer. A transformer AC-couples an audio signal directly into the DC supply to ...
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1answer
52 views

How phase modulation changes spectrum?

I'm studying amplitude,frequency and phase modulations for an exam. I just studied amplitude and frequency modulations, however i didn't succeed in understanding how the phase modulation changes the ...
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19 views

Determing proper wireless parameters for HMTRP radio module

I'm trying to properly setup an HM-TRP FSK radio module to send and receive data the best it can at 56kbps. I think I'm wrong with setting it up to use 600Khz "receive bandwidth" and 160Khz "modulate ...
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32 views

Delta modulation slope overloading

I have a question about a problem in a textbook I can't exactly solve. It goes as follow: Given a message m(t) as input to a DM system $$ m(t) = 3cos(890\pi t) - 0.7sin(1000\sqrt{3}t) $$ Determine ...
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2answers
76 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) \$ ? ...
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1answer
107 views

What is the physics behind width of the duty cycle in Arduino?

I was wondering if someone can tell me how Arduino changes the width of the duty cycle? How it produces an on-off pattern? I am looking for an explanation for modulation in this system.
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2answers
934 views

Why are the resistors in an AM modulator necessary?

In preparation for the amateur radio exam, I have been following the preparation course material by DJ4UF. In the section about modulation it presents this diagram of a simplified AM modulator. The ...
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27 views

Sinusoidal Pulse Width Bipolar Modulation Scheme : Harmonic Spectrum

I was reading about the SPWM Bipolar Scheme for inverters the book said that we choose the frequency modulation ratio be odd to obtain only odd harmonics. What happens if we choose the frequency ...
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1answer
56 views

LoRa modulation and chirp process clarification

I am new to LoRa and I would like to get some confusion on chirp-based modulation process clarified. I was reading the very good thread Understanding the relationship between LoRa chips, chirps, ...
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10answers
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How exactly does AM/FM carry both pitch and loudness of voice?

Almost every tutorial on AM/FM modulation shows the modulating signal as something like a simple tone or continuous sine wave. Now that's easy, and for AM you just superimpose the modulating signal ...
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2answers
99 views

Converting from OOK to ASK at 433MHz

I need to convert messages sent from a device using OOK modulation to ASK so it can communicate with another device that modulates in ASK. I can't modify either of those devices. I was wondering if ...
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22 views

M-PSK modulation

From what I read the sigma value for 4 psk modulation is sigma=sqrt[1/(2*SNR_LINEAR)] But when you add the average energy of 4 psk which is given by [1+0i;0+1i;-1+0i;0-1i] this gives you 0 so how ...
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1answer
74 views

Generating a 10MHz modulated signal [closed]

For an application I need to generate a 10 MHz sine wave signal that is modulated with 20 KHz triangle signal. This is going to be frequency modulated. This goes into another circuit which require a ...
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3answers
1k views

Why do spectrum analyzers use envelope detectors?

Spectrum analyzers can usually be represented by the following block diagram: Before entering the video filter, the signal passes through an envelope detector. What I don't understand is why this is ...
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1answer
75 views

wifi baseband access

I've got an unusual use case (optical communications) that would benefit from access to the wifi baseband signal before it is upconverted/modulated at 2.5Ghz. However most modern wifi chips combine ...
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2answers
122 views

Understanding PLL performance: PFD output bandwidth

For an application I need to FM modulate a signal with a 10 MHz bandwidth. Due to constraints I have no control over, I have to do it in an analog way (so I can't just digitize the signal, IQ modulate,...
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1answer
40 views

Amplitude Spectrum of FM wave from Bessel First order

given the values for \$\beta=5\$, for the Bessel of the first order: \$ J_{0}(5)=-0.26, J_{1}(5)=0.34, J_{2}(5)=0.49...\$ in order to plot the amplitude spectrum of the FM wave, do you treat the ...
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1answer
117 views

Benifit of Delta Sigma DACs

I've researched much about the delta sigma ADC and understand to some extent its workings. The delta sigma modulation in the ADC allows for increasing the ENOB by increasing the SNR through noise ...
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3answers
192 views

Signal multiplication in AM transmitter circuit

According to Wikipedia, amplitude modulation is achieved by multiplying the carrier signal with message signal. Where is this multiplication performed in this AM transmitter circuit? It seems to me (...
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1answer
49 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
72 views

How does the AM modulated wave cancel out when the signal amplitude exceeds carrier wave amplitude?

In AM modulation, the ratio of signal amplitude to carrier wave amplitude is called modulation index as m. When m>1 i.e when signal amplitude exceeds the carrier wave amplitude the modulated wave ...
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1answer
142 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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38 views

Phase modulation and intermodulation anomaly **plots attached**

I have a MATLAB script for modelling a two tone signal (a sum of two sinusoids) going through a non linear transfer function (such as an amplifier). The amplitude of a signal is amplified non linearly,...
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1answer
50 views

Modulated IR for optical transmission of encoder data (TSOP 4840)

Some background: I am a mechatronics engineer and I have just recently started my first job out of university as an electrical engineer. I feel a little out of my depth but I wasn't going to turn the ...
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36 views

Why the result of stepped-frequency continuous radar result does not match with the outcomes found in literature?

I have a confusion about frequency modulated signal based radars as follow; In literature two-way delay related to the target is defined as; $$ \tau(t) = \frac{2R}{c} $$ and transmitting signal is ...
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107 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
56 views

Is possible to modulate the upper and lower sides of a carrier with two distict signals?

I would like to modulate in amplitude the upper and lower sides of a carrier with two distinct signals. Would it be possible? There is a specific name for this scheme of modulation? The detection ...