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Questions tagged [modulation]

Generic term for coding information onto another carrier signal

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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
37 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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27 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
46 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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35 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
51 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
107 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
28 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
343 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
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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
48 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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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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28 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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73 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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27 views

Equivalence of frequency and d(phase)/dt?

Since frequency is the time-derivative of phase, I expect to be able to replace time-varying phase by adding its derivative to a carrier frequency, but I don't get equivalent answers when I simulate ...
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1answer
104 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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889 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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24 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
48 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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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
84 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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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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Complementary Code Keying and DQPSK

I am confused on how DQPSK is used with Complementary Code Keying (CCK). Does this mean that after 8 bit code word is generated, every two bits of code word are sent sequentially with DQPSK?
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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
62 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
113 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
36 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
97 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
177 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
34 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
63 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
116 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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37 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
48 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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0answers
34 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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88 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
55 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 ...
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1answer
47 views

Vestigial Side Band Demodulation: Which components are to be retained and which are to be filtered out?

This article shows the analysis of Vestigial Side Band Suppressed Carrier demodulation. I have understood the mathematical derivation up to eq (1). However, I am unable to understand which components ...
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339 views

Square Law demodulator. How to extract the term \$m^{2}(t)\$?

We are trying to extract the message signal from the AM signal using square law demodulator. In the final expression, \$V_2(t)\$, the term encircled in blue has to be retained, and the others have to ...
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1answer
95 views

Modulation ideas for old and long analog bus cabling

Need some feedback on techniques to make an old analog bus work with bidirectional data(half duplex is fine) at speeds upto 256kbps The cable itself is a shielded twisted pair with a nominal ...
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2answers
327 views

Question about digital modulation

So there are several ways to transmit a bitstream but where is the actual info when my carrier is a sinewave? My basic understanding is we have symbols (phase,amplitude or frequency), we assign bits ...
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1answer
2k views

AM Modulator with BJT 2N3904

I created an AM modulator circuit with BJT 2N3904 for a school project. V1 is the modulating signal (sine wave, amplitude 5V, frequency 1KHz) V2 is the carrier signal (sine wave, amplitude 30mV, ...
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52 views

Why is the factor d involved in the bandwidth when doing amplitude shift keying?

In the book by Forouzan, under the section Bandwith for ASK( chapter 5), it's given that However, there is normally another factor involved, called d which depends on the modulation and filtering ...
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1answer
32 views

Is a cross-correlation property of Gold code independent to modulation?

Gold code is known to have a good cross-corrleation property, i.e., a high cross-correlation value shows iff two sequences are the same. I wonder whether it is independent to modulation, e.g., BPSK, ...
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2answers
143 views

How to create an OOK signal in ADS

I'm trying to make an OOK modulated signal in ADS. I need a random bit generator, and a block to multiply a sinusoidal signal with that random pulse. I did this in Cadence by the 'rand_bit_stream' and ...
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1answer
189 views

direct conversion SSB (vs DSB-SC)

While I understand the problems trying to demodulate a DSB-SC signal using a direct conversion scheme, mostly the phasing issues arising from the fact that the sidebands are symettric and in ...
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1answer
43 views

LED dimming and modulating with two PWM signals

I have a need for an LED, driven by a constant current source, that can be smoothly dimmed and also semi-rapidly (say 2.5kHz) modulated for later bandpass filtering. I've designed a possible circuit, ...
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1answer
197 views

What is current modulated laser driver? What does it do to the laser?

The title is actually one of the many questions I have. I've started to work on a project that includes lasers. I've worked with lasers and fiber optics before and I even constructed a simple constant ...
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2answers
79 views

Questions on load modulation, Doherty PA

I was unable to understand a bunch of stuff related to amplifiers. Specifically my questions are as follows: What is load modulation? If i have a load of impedance of 10 ohms physically, then does ...