# Questions tagged [modulation]

Generic term for coding information onto another carrier signal

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### Why is the op-amp able to eliminate negative voltage?

I have a circuit with the attached waveform. Can someone please explain why the 2nd op-amp (middle) is able to eliminate the negative voltage? By reasoning and analysing the circuit I can see that the ...
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### How would a modulated and demodulated signal differ in FM and PM? Simulink Simulation

I am trying to observe the differences of phase and frequency modulation. On the figure below, the left scope shows a frequency modulation and demodulation whereas the right scope shows a phase ...
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1 vote
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### What is the function of frequency resolution in multisim

In this circuit, noticed if the frequency is set to be the same as source frequency, the display will show a constant peak. The modulation index is 0.6. However, if the resolution frequency is set to ...
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1 vote
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### Downconversion Intermodulation Frequencies - Where do they come from?

I recently came across this video which discusses the downconversion of a signal (referred to as IN) to an Intermediate Frequency (IF) using a Local Oscillator (LO). I'm assuming that all of these ...
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1 vote
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### How is a GPS receiver able to calculate SNR?

I know that there is a certain relation between bit error rate and SNR for every modulation scheme. But i wonder how a GPS receiver can measure bit error rate and how it able to calculate SNR (I could ...
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### Why is Line coding called "Line coding"?

Why is line coding also called digital base band modulation named "line coding" where does it come? and how is the name it to modulation
1 vote
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### How does a phase shift keying receiver detect when a new incoming modulated signal is at the input?

This is not a math question. What I want to know is the physical implementation of the receiver where phase modulated signal is coming to the receiver. How does the receiver decide when the phase ...
37 views

### Apsk modulation in lt spice

Greetings according to the schedule, help to do APSK modulation in LTspice. I built oscillators and the ideal AM modulator but whow make variations for amplitude and phase become 16-apsk is my biggest ...
44 views

### Digital isolator OOK and edge-based encoding supply current consumption

I am reading this article the use of robust digital isolators in the harsh environments of electric motor drives and it says pulse encoding uses more supply current at higher data rates than 10 Mbps ...
61 views

### FOC and Inverter modulation techniques

I'm not sure I understand how FOC and modulation techniques work together. If I understand properly, the output of the FOC algorithm is the required voltage at each phase of the motor that is given ...
1 vote
65 views

### Recommendations for modulation of VCSEL laserdiode configurations

For my project I need to design a cheap VCSEL laser driver which can be modulated up to 10 MHz. My laserdiode is VCSEL-1550 nm-T (built-in TEC and no monitordiode for APC). Datasheet link is here: ...
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1 vote
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### Frequency Modulation - Why don't we modulate the carrier by multiplying message signal m(t) directly with f_car?

I am master student of computer science and I have got a problem/question from the domain of communication engineering. So: I'm listening to a lecture that's about Layer 1 stuff, and recently we ...
2k views

### How much data could be stored on a standard compact cassette using modern encoding?

My father and I recently dug out his old Commodore 64 from his basement and tried to revive it. Among other accessories, we also found his old Datasette drive, which is essentially a normal tape drive ...
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### What are the M and N values when modulation formats (QPSK,8QAM) are polarization multiplexed?

I always get confused in the terminology of modulation level (M) and number of bits per symbol (N). Please correct me if I am wrong. Because with these values, my question extends to polarization ...
543 views

### How to design an amplitude modulator with common-emitter amplifier circuit?

I am facing a problem on how to design an amplitude modulator using a common-emitter amplifier circuit. I am asked to use a carrier frequency of 50MHz and an input signal of 1kHz to 14kHz. In order to ...
1 vote
100 views

### Modulator in lasercom: from theory to practice

Hello everyone! We are working on a realisation of an optical modulator and have a doubt. Mr Noel Miller posted already a question, but it was suggested this community. I will repost his question ...
1 vote
126 views

### Extracting two signals from a photosensor

I have a circuit that pulses two LEDs on and off at the same frequency but out of phase. I would like to find a hardware solution for using one sensor to measure separately the intensity from each ...
244 views

### Real-world CQI-to-MCS and SNR-to-CQI tables?

How can I get real-world CQI-to-MCS and SNR-to-CQI tables? I am particularly looking for 5G-NR or LTE-A related tables. Can someone share any references? Edit: I had found one table for CQI-MCS ...
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### Frequency Modulation Voltage Formula Derivation

I am taking Keysight "Signal Generation and Digital Modulation" Webinar. In class, frequency modulation is described in the slide below. The modulated (carrier signal added with transmitted ...
251 views

### SG3525A for modulating an audio signal for a class D audio amplifier

I am using the SG3525A IC to modulate an audio signal into PWM that is then used to drive MOSFETS for a class D audio amplifier. I have managed to design a circuit that outputs a 10kHz PWM signal. I ...
259 views

### What is the simplest 100km RF communication link there is?

I am looking for a technology for sending sporadic bytes over RF hundreds of kilometers away - assume line of sight. What should I look into to do that? What frequency? What modulation? Perhaps what ...
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### Backscatter in RFID

I am reading and trying to understand about the RF ID communication. I read that the receiver conveys the binary data back to the transmitter using backscatter modulation. But I find it a little ...
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1 vote
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### What does 'rotating vector addition' mean in this context, and how does it generate AM and FM?

I am currently learning about wave modulation. In communication theory, it is said that 'rotating vector addition' generates AM (amplitude modulation) and FM (frequency modulation). What does '...
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### Hearing the radio by touching a jack plug

Here is what happened to me a few days ago: I own an amplified speaker with a jack plug. Usually, when I touch the jack plug with my finger I hear a "hum" sound. On this specific day, on a ...
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183 views

### How to calculate subcarriers bandwidth and cyclic prefix length in an OFDM using the IFFT

I'm trying to understand how OFDM works thanks also to the Simulink OFDM block. Now, I have understood that the OFDM modulation "convert" a faster bit rate using a certain bandwidth into a ...
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1 vote
56 views

### Minimum value of A to be able to use envelope detector in amplitude demodulation when m(t) includes an exponential

This is one of the exam questions I have come across with. My approach was, To be able to get detected by the envelope detector, $$A\geq |\max(m(t))|$$ Max value of m(t) is 1 right? When t = 0 we get,...
83 views

### Find the total amount of frequency multiplication needed for an Armstrong indirect FM modulator, when frequency deviation is adjustable in a range

I am currently practicing for my college exams and in this question, they are asking us to find the total multiplication needed in the system. But I am stuck because I have no idea of how to make use ...
110 views

I'm trying to build a radar that functions in the ISM bands (433 MHz, 915 MHz, 2.4 GHz and 5.8 GHz). I'm trying to look for RF transceiver ICs that operate in these bands. Most of the ICs I'm finding ...
216 views

### How is the measurement light frequency shifted with respect to the reference light frequency by some carrier frequency in practice?

I've been studying heterodyning in interferometry. My understanding is that heterodyning is achieved by shifting the measurement light frequency with respect to the reference light frequency by some ...
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### Failed to get desired output of a pulse width modulation circuit simulation

I was given an assignment to simulate this circuit by first adjusting the variable resistor to get V=0 at the non inverting end of the opamp then observe the waveform at the output. I am getting an AC ...
80 views

### How to get the desired signal from a photodiode and phototransistor multisim?

The above is a visualization of an IR transmitter and receiver circuit I'm building. Sending a 2v and 1khz sine wave through a photodiode to a phototransistor. The figure above shows the outputs I ...
174 views

### Stm32 dma for IQ modulation

I’m trying to develop an application where I use an stm32f405rgt6 microcontroller ic to drive a radar that operates in multiple ism bands (433.92 MHz, 915 MHz, 2.4 GHz and 5.8 GHz). The overall idea ...
110 views

### Modulating frequency of a crystal oscillator circuit

I have built this simple Crystal Oscillator circuit operating at 30Mhz and it's working fine. Please ignore the values of the equivalent circuit of the Crystal i.e ESR, EPC, ESC, ESI. I am using this ...
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### why do i have to add a capacitor to observe AM output

so our TA asked us to simulate this modulator in lTspice but told us to add a capacitor that has a value of 0.1 uF at the output and record the result and confirm the envelope shape from message ...
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### PLC carrier frequency

I am trying to build a communication system over a power line using FSK. I want to stay within the frequency band A of the CENELEC protocol which goes from 3 to 95 kHz. I am trying to determine ...
128 views

### What is the equivalent LTSpice diagram of the given varactor diode modulator (FM)

Given below is an example of direct FM generation using varactor diode modulator. What is the equivalent circuit of this in LTspice? Can you explain the given circuit?
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### What is the percentage modulation of phase modulation PM?

What is the percentage modulation of a phase modulation (PM)? Can you further explain and give detail? I am currently stuck in finding the information about this
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I am trying to envision the circuit which will allow me to get PR-ASK modulation. Fundamentally there are two ways to produce the PR-ASK; Toggling digital data between +- V and mixing it with CW at ...
78 views

### IR modulation with photodiodes multiplexing

I have 100 IR photodiodes that I would like to multiplex to one (or the fewest achievable) transimpedance amplifier(s), both for space and price constraints. I am aware of the capacitance and noise ...
87 views

### Transmiting analog signal with lora

I want to transmit an analog signal over Frequency Modulation with a Lora RA 02 module. First thing I need to do is convert the analog signal from the audio source to digital, right?. But I had so ...
1 vote
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### DDS NBFM transmitter design

As a design exercise I'm trying to come up with a design for NBFM. I'd like to stick with digital domain as much as possible, since that's what I know best. I'm familiar with RF enough to know that I ...
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### Why does a phase shift happen in the demodulated AM signal using envelope detection?

I was studying AM signal demodulation using envelope detection with the circuit shown below. In the book it says the low pass filter part is called a post-detection filter and that this filter causes ...
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### Difference between O-QPSK with half-sine shaping and MSK?

The IEEE 802.15.4 standard specifies that O-QPSK modulation with half-sine pulse shape (HSS) should be used at the 2.4 GHz band. But according to Wikipedia, O-QPSK modulation uses square pulses, and O-...
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### Figuring out transmission protocol in cheap wireless door bell

Due to boredom I've tried some reverse engineering of simple cheap wireless ring bell which uses 433.92MHz transmitter and receiver via OOK modulation. It sends several times the same information. On ...
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### What's the relationship between bandwidth and symbol rate for a modulated signal?

I was hoping somebody could help me with understanding the relationship between the bandwidth of a modulated carrier signal (say using QPSK) and the symbol rate(s) you can transmit across a channel. ...
130 views

### Bias T for modulation of VCSEL laserdiode

For my project, I would like to design a Bias Tee for a VCSEL laserdiode, because a modulation is required. The bandwidth is 20 KHz - 10 MHz. My steps are shown below: As a reference, I have used the ...
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### Mobile Signals and Amplitude Modulation

I was just introduced to the concept of Amplitude Modulation and how it was used for transmitting information between radios. What modulation technique is used for communication between mobile cell ...
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### Designing differerntial Sigal modulator

I would like your suggestion on my first design Differential signal modulator [simulation attached]. Before jumping into design let me highlight my objective. I am differentiating a control signal of ...
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### Spectral properties of QPSK modulation

From what I've read, the spectral properties of the modulation largely depend on the rate of change of the signal phase - "a signal in which the phase changes stepwise has a broad spectrum, well ...
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