Questions tagged [modulation]

Generic term for coding information onto another carrier signal

47 questions
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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 $X(w - w_c)$ ? ...
66 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 ...
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 ...
27 views

Double Balanced Mixer

Consider this double balanced mixer: Its output contains only the frequencies generated by the product of those of LO and RF signals, where LO is supposed to be a large signal (which switches ON and ...
37 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 ...
89 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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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 ...
19 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, ...
76 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, ...
62 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 ...
170 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 ...
82 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 ...
147 views

Is there a pulse shaping after OFDM modulation in NB-IoT?

Just as the title says. I have searched for a whole day and haven't found any confidential materials to verify whether there is a pulse shaping after OFDM modulation in NB-IoT? For example, in https:/...
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AM modulation circuit modification

I have an assignment on AM modulation. I implemented a circuit and the output wasn't exactly correct, the output is not symmetrical about the x-axis. I'll post screenshots which might explain the ...
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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) ...
92 views

Vibrato audio effect circuit

I would like to build a circuit that adds a "vibrato" audio effect to a simple sine wave input. Sample audio clip from Wikipedia: Vibrato, Sound Frequency 500Hz, Frequency Modulation 50Hz - Vibrato ...
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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/...
338 views

Output of Oscillator and Modulator is Absent

I am designing circuit of AM transmitter. This circuit I got from youtube. You can have it from here I designed the same circuit in proteus and simulate it and try to obtain different waveforms on ...
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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 ...
43 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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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 ...
135 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 ...
120 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 ...
330 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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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 ...
66 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 ...
124 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 ...
595 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 ...
50 views

Bandwidth for a Butterworth filter

How to choose the bandwidth of a 2 pole Butterworth filter for QPSK modulation? What bandwidth should be chosen, if symbol duration is 10 ms? How to limit ISI for QPSK modulation?
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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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Data rate with modulation and conventional encoding

I had a rather simple question. Say I had a SISO communications system with an information data rate of 50 Mbps that uses QPSK modulation and a rate 1/2 conventional coding. What would be my symbol ...
17 views

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 ...
40 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 ...
26 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 ...
51 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 ...
135 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. ...
130 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 ...
34 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 ...
20 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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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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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,...
138 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 ...
279 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 ...
89 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 ...
232 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 "...