# Questions tagged [modulation]

Generic term for coding information onto another carrier signal

332 questions
116 views

### Drawing basic AM signal [closed]

I am confused with how to draw the following AM signal: S(t)=6cos(12t)+3/2cos(14t)+3/2cos(10t)
355 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 ...
258 views

### How can IR frequency modulation be used to detect distance?

The new TSSP4056 proximity sensor from Vishay "determines distance by varying the carrier frequency used to drive the emitter between 30 kHz and 54 kHz, thereby finding the threshold frequency at ...
77 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 ...
441 views

### Why does this IR receiver not receiving some signals?

I am trying to read some IR signals. There is a synchronizer emitting modulated IR signals. And my receiver must receive those signals and interpret them. Actually, there are only two different ...
68 views

### LM1496 maximum input voltage

one last question like that. I have the LM1496. The datasheet says that the maximum input voltage is 5V. DATASHEET The question is why is this true? What determines these 5V limit? Thank you!
4k views

### What are the advantages of DSB AM with carrier?

I saw an exam question that asked what the advantages of using DSB AM with carrier are. I can't find anything conclusive in my books or by googling. It seems to me that DSB AM with carrier is less ...
1k views

### Differentiating between 32-QAM and 32-PSK

A communication channel with 4 kHz bandwidth requires 40 kbps data rate. What is the most suitable modulation technique to use in this particular scenario? for this I used the Nyquist theorem. C=2B ...
1k views

### Basic AM modulator circuit?

I am having trouble finding a good resource for understanding the design of a very basic AM modulator circuit. Specifically, I am using a simulation tool which provides an AM wave, which consists ...
335 views

### XY graph modulating/demodulated signals in FM

I am using Labview to simulate a communication channel using FM modulation/demodulation (with MT Modulate FM VI and MT Demodulate FM VI to be more precise). I made a XY-plot (see below) showing the ...
88 views

### How to fix a frequency shifted audio part of an RF signal?

I tried to connect an old Japanese (NTSC, System M) video gaming system (an original Famicom, HVC-001) to a rather modern multisystem LCD TV-set (Sharp LC-43CFE5222E). The TV tuner is capable of ...
198 views

### Analog circuit for multiplying in the frequency domain [duplicate]

I have an idea I want to experiment with - doing boolean logic with analog (OFDM) signals. Each frequency component represents a different 'bit'. A key factor is performing the AND operation. I would ...
1k views

### Comparison between FMCW radar modulation techniques

In designing a Frequency modulated continuous wave (FMCW) radar system for target detection, there is a possibility of choosing the modulation technique amongst triangle or saw-tooth modulation. What ...
63 views

### Is Turbo decoding modulation dependent?

I want to use the BER result of a turbo coded system from an article, but my system is not BPSK (and the article has discussed just the BPSK case). Now I wonder is Turbo decoder, modulation dependent?
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### Controlling initial phase of carrier during modulation?

During the process of modulation, any of the three parameters, viz $\ A_c$ , $ω_c$ and φ, of the carrier wave can be controlled by the message signal where φ is the initial phase. How is it ...
4k views

### Operation of LC circuit in Frequency Modulation with simulation and linking it to the basic principle of frequency modulation [duplicate]

Can somebody help how message signal (words spoken near microphone) is modulated using LC circuit and how lc circuit oscillates at particular frequency by applying dc voltage. In the below circuit l1 ...
869 views

### Why FM stereo uses DSB-SC instead of VSB?

Using vestigial sideband instead of double sideband supressed carrier could make the baseband stereo signal more compact. Would there be any other benefits or downsides of employing VSB?
374 views

### Why doesn't Class C modulator operate in saturation?

The following circuit is a class C (actually class B) amplifier used in AM modulator in my previous question. According to the textbooks, the transistor is driven into saturation in this class. A ...
3k views

### Analysis of Class C AM modulator

The following schematic is a class C AM modulator without use of any transformers I've just changed the parameters in spice to get a correct modulation. however I want to find the theoretical value ...
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### Help identifying modulation scheme

I'm trying to identify the following modulation scheme being used to transmit a infrared code. It looks like manchester, but there's some gaps where there's no transitions. The code being ...
254 views

### Gray coding for 8-triangular signal constellation

I'm trying to find the gray coding for the 8-triangular signal constellation below, but no matter what I try, one of the neighbors always has 2 bits differing. For example, two of the neighbors for ...
2k views

### How to modulate a LED to send data and recieve with a photodiode

What is the concept of modulating a light source (white led, IR led, etc) to send data and then demodulating it with a photodiode back into data? I am wanting to experiment with trying to use IR/...
520 views

### Retrofit a Hi-Fi remote with a RF 433 MHz module

In the past I used a remote for a AIWA Hi-Fi to control a AVR processor and circuit I custom made. I used an infrared receiver from Vishay (tuned on the 38 kHz) to demodulate the signal, then fed to ...
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 ...
180 views

I'm trying to undestand the role of the Bessel differential equation in calculating the side bands of a phase modulated signal. I started out with the textbook example $$u_{PM} = cos(w_C \cdot t + \... 1answer 641 views ### QAM demodulation , hard vs soft if there is any I am trying to find the answer to , what types of demodulation methods are exists. Each of my searches results with different names, but converging to one metric , which is finding the closest symbol ... 1answer 653 views ### Transmitting data over inductive charging coils (or boosting RFID/NFC power supply) I know that data can be sent over power lines through various different types of modulation - that is as far as my knowledge ends. I have a small D.I.Y. project (a board game) that requires some form ... 1answer 201 views ### Definition of $\mu$ I have a question as follows. This is not a homework question I just need to clarify my doubt on how this modulation index is defined. Suppose a 2kHz audio tone having 2V amplitude is to be amplitude ... 1answer 335 views ### Why is the modulating shape appear in both sides of the carrier signal in AM? It's about Amplitude Modulation. Can anyone tell me why is this signal wave or modulating waveform shape appears in both sides of the carrier sine wave? Why not in one side only?$$x_c(t) = A_c[1 + \...
467 views

I have a simple radar module (k-band) that is capable of fm modulation and it provides both I and Q as baseband outputs. I like to extend the measurement range of this module by just signal processing ...
1k views

### How is FM modulation is achieved using a single BJT

I want to understand how this circuit achieve frequency modulation. The BJT is a 2N3904. I found that millers effect comes into play and varies the frequency of the tank circuit about a center ...
270 views

### Power requried for M-ary modulation schemes

When we go for M-ary modulation schemes like QPSK etc, does the transmission power increase with M? Why?
1k views

### Does a carrier wave need to be sinusoidal?

I am trying to AM modulate a song and I have an idea of how I am going to do it, but I need a carrier wave to start with and I've been having trouble creating one with a ceramic resonator because I ...
832 views

### Carrier generation at receiver in DSB-SC modulation?

As shown in fig., In this scheme input signal is square and passed through a narrow(high Q) bandpass filter tuned to $w_c$.Finally the ouput comes to be a sinusoid of frequency $w_c$. But to ...
381 views

### Frequency Modulated Continuous Wave Radar: Basic Confusion

I was reading about Frequency modulated Continuous wave radar but still struggling to understand it. I have a few questions in the slide above. The blue line in the graph represents the transmitted ...
832 views

### How does modulation technique affect channel capacity?

Shannon's channel capacity formula does not consider modulation techniques. How then does LTE achieve high data rate using advanced modulation techniques? P.S: I am novice in RF and signal processing....
132 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 ...
455 views

### 24GHz Mixer - How to shift the frequency of a 24GHz(100MHz bandwidth) signal by +-4kHz

Why do I want this? When a 24GHz radar signal hits an object that has a relative velocity, the frequency of the signal will shift by a frequency on the order of kilohertz. I want to create this ...
440 views

### Matlab: Channel coding and modulation [closed]

This is a beginner level question on understanding modulation and channel coding. The confusion arises when I am trying to implement the concepts. Let's say I have the information bits as ...
125 views

### Find Power Spectral Density of given signal

I am given a question with very brief notes to study from. The question is this: Now I was wondering, are the following part of the notes relevant at all: Is this the appropriate method to solve the ...
3k views

### Why can a single sine wave signal be used to send digital data but a composite signal is needed to send human talk,etc.?

I can understand the following text (Data Communications and Networking: 4th Edition, Berhouz Forouzan, Ch.5, page 179) which says that a property of a single sine wave carrier signal (phase, ...
2k views

### FM transmitter design?

I stumbled across a relatively simple FM radio transmitter online. Credit: makezine.com I wanted to understand how it works (it is called "super simple" on the website), but several hours I have ...
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 ...
717 views

### What's the advantage of PAM modulation over QAM?

What are the main advantages of PAM (Pulse amplitude modulation) modulation over QAM ? Ethernet is using PAM for 1000BASET and 10GBASET, but any other high speed links use QAM like DOCSIS, ADSL/VDSL ...
266 views

### How are the original signal and the AM signal related?

Use the TIMS “Variable DC” module to generate a 1V DC signal. Use the “Adder” module to add this DC signal to the message signal generated in task 1 (this will produce the ...
6k views

### If an FM signal has different frequencies, how does the radio receive the signal in a fixed frequency?

If an FM signal has different frequencies according to the modulation, how does the radio receive the signal in a fixed frequency like 103.2 MHz?
89 views

### About the combination of two signals with capacitors

Here is a link of an article I've been reading. http://www.analoguehaven.com/moog/thereminblack/hotrod.pdf In page 4 there is a circuit schematic. Notice there is a part called variable pitch ...
287 views

### Orthogonal Frequency Division Multiplexing (OFDM)

I am not a professional but I'm trying to figure out how OFDM works. It is clear to me that OFDM works with closely spaced subcarriers with orthogonal frequency. Each subcarrier gets modulated with a ...