# Questions tagged [modulation]

Generic term for coding information onto another carrier signal

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### RFID data transfer rates?

I'm learning about RFID and am trying to figure out what the data rates are for the different types of RFID technologies. I've learned that there are three different frequencies tags and readers ...
2k views

### How does this direct digital synthesis accumulator work?

So, I grabbed some code online and morphed it to work with my DE2-115 board, and now I need some help understanding exactly how it works. ...
41k views

### What is Overmodulation?

The Wikipedia article is very short and doesn't explain the concept very well, and there aren't any other sites that I can find that give a simple explanation. What does it mean by 100% modulation? I ...
121 views

### the implementaion of communication systems [closed]

I wonder , Why when we study communications systems , we just study the theoretical part(Math) , and we never touch the electrical circuits that used to implements this systems , I have asked my DR. ...
1k views

### How to demodulate an overmodulated signal?

Say I have an overmodulated signal like the example above. When you demodulate this you will get distortion. Is it possible to somehow demodulate this?
151 views

### finding out the bandwidth of m(t)*m(t) if the bandwidth of m(t) is a known quantity

m(t)*m(t) in time domain is equivalent to the convolution of m(w) and m(w) in frequency domain.Thus if the bandwidth of m(t) is a known quantity then how is the bandwidth of m(t)*m(t) is determined?
4k views

### DSB-SC modulation circuit

I have the following circuit which is used for DSB-SC modulation but, I can't understand Why we use High Pass Filter(I expect to be High pass filter , I'm not sure with that ) at the carrier ? Why ...
1k views

### BLE113 Bluetooth 4.0 module with CR2025 3v battery power supply

A question regarding the power supply of a BLE113 Bluetooth 4.0 module: I am attempting to order several bluetooth modules, but the main concern is the power supply. Since I am new in the field of all ...
275 views

### What is the modulation technique used?

I own a Tx/Rx Radio Direction-Finding (RDF) set for a sport called falconry, basically, locating & recovering a pet falcon after flight. The Tx tag is at 218.025MHz from Marshall Radio Telemetry :...
33k views

### RC time constant and diode detector

For a better detection of the modulated signal with the diode detector below, one requirement is that the time constant of the RC filter conforms to:  \frac{1}{\omega_{c}} \leq RC \leq \frac{ \sqrt{...
189 views

### Why more bandwidth means more bit rate per second? [duplicate]

According to this link ( and some other sources I have found ) more bandwidth on a wire means more bit rates per second... Can someone try to explain why this is so as simple as possible? This is ...
472 views

### How to increase frequency modulation index?

I'm thinking of making a low power FM transmitter. Here's a diagram. It seems an absolute pull range of a VCXO will limit the modulation index. Is there possibly a way to extend it?
193 views

### How can I toggle a astable 555?

I'm using a NE555 running at 37KHz to generate a carrier frequency for transmitting IR. Now I need to modulate it using OOK, I know that are various ways to toggle it. The most obvious way is to ...
98 views

### How much gain for optical open-air receiver?

I am planning to make an experimental communications system. I will use a high power LED (ā3watts) Amplitude Modulated with a sound signal and eventually Pulse modulated with digital data for the ...
912 views

### The relation between light electric field and light power (optical modulation)

I have been keeping thinking this question for one week. Hope could get some help from you. Light 1: Electric field = $\text{e}^{j\omega t}$; Power = $\frac{1}{2}A^2$ light 2: \\$ \alpha = \...
757 views

### Determining type of modulation

The circuit below is a radio transmitter circuit of a typical RC car. The circuit makes use of IC TX2 encoder. The output of IC ("SO" pin) is a series of pulses at low speed (84 Hz). This signal will ...
28k views

### RF Bandwidth vs Data Rate (modulation)

I was reading some articles about digital and analog modulating processes. One of them was this: Modulation techniques At a certain point is says: The bandwidth produced is a function of the highest ...
586 views

### Signal encoding on Realtek TX2 IC

I 'm trying to figure out the way IC TX2 encodes different signals (RIGHT, LEFT, FORWARD, BACKWARD, TURBO). I can understand that presence of voltage means an appropriate signal to be transmitted. "...
703 views

### Is there an easy way to multiplex the state of multiple switches in an AC circuit?

If I had a circuit like this... *Blurple boxes represent unknown devices/circuitry What would be the simplest way to transmit the states of the switches, using only a single wire? In essence I'm ...
1k views

### Amplitude modulated wave weird display in oscilloscope

In my lab experiment (http://www.ele.uri.edu/courses/ele436/labs/expA2.pdf), My amplitude modulated wave is not displaying the vertical lines-the high frequency waves of carrier (as shown in ...
22k views

### How is digital information encoded/decoded in light or radio waves?

I know exactly how DAC and ADC works; that's not my concern. What I am asking is how the constituent state of matter (and the "states" represented by them) in a circuit can be transferred to a set of ...
782 views

### Adding LFO Modulation to VCA in synthesizer

I just started sketching ideas to add LFO to VCA modulation in a device that already has a VCA circuit employed, but Iāve run into a snagā¦ I can design a circuit to give proper modulation at full open ...
2k views

### Advantages of a Gray code in 16-QAM

I'm looking at a system using a gray code on 16-QAM. When a symbol changes, you move from one of the 16 symbols in the constellation to any of the 16 symbols. I'm wondering if there is in fact an ...
317 views

### Help design multiplication / modulation stage

I'm a self-taught amateur analog electronics enthusiast, I wonder if I can get some basic help on a simple circuit to demonstrate an interesting mathematical concept. (Not a homework assignment, but a ...
691 views

### Amplitude Modulation Concepts

I am currently learning about telecommunications but I have some concept issues. Firstly, does it matter if I am using cosine or sine in the equation? I understand that they are basically the same ...
3k views

### The concept and circuit of 2 to 4 level converter in 8-QAM

I have a difficulty to understand the basic concept about 2 to 4 level converter in 8-QAM. I've google it but still don't understand much except this block is used to convert two voltage into 4 ...
20k views

### Using Bessel function graph to finde out side bands

If I am not wrong, using Bessel function we can estimate the side bands of a carrier? Is this correct? If so, what are the steps to find these values from the graph? For example if modulation index ...
144 views

### Modulation that is used in WiMAX [closed]

Which modulation is used in WiMAX? And how does it work? I found QAM-64 but I'm not sure about that.
4k views

### Tradeoffs between QPSK and BPSK re. spectral efficiency, error rate, etc

Say I'm using binary phase-shift keying (BPSK) to transmit some data at some rate. Now say that I want to double the data rate, without increasing my transmitter power. I could either continue to use ...
10k views

### What is the Need for modulation

What is the need for any kind of modulation in order to transmit signals?
158 views

### Confusion with modulation/demodulation

I am following a book: Data communication and networking (Behrouz-Foruzan). It says that modulation means building a bit stream from an analog signal. However as far as I understand it's the ...
717 views

### UHF Phase Modulation

I would like to design a system that produces -10 degrees and +10 degrees phase shifts at 409.6MHz (Basically BPSK). The way I'm thinking about approaching this is by using a DDS to generate the BPSK ...
1k views

### Question about FM and PM and Angle Modulation

I am having a bit of trouble understanding how FM works mathematically. I fully understand the conceptual basics regarding how information is transfered by modulating the frequency, but what I don't ...
376 views

### relationship between modulation index and carrier-suppressed condition in fm

What is the relationship between modulation index and carrier-suppressed condition in FM. What should the modulation index be when the carrier is suppressed in FM?
2k views

### Arduino beacon for IR Seeker v2 (Mindstorms NXT Sensor) - Pulse IR at 38Khz Carrier and 1200 Frequency

I hate to ask a question like this, that is kinda just like "give me the code" but seriously. I've tried reading up on it everywhere, and I just don't seem to get a thing of having both a carrier ...
840 views

### Information required in building DIY HHO production device [closed]

I am going to try producing HHO (creating hydrogen and oxygen) and have been told that a "100 Amp 12 volt pulsed wave modulator" will increase the HHO production. I believe they mean pulse width ...
537 views

### RF transceiver WITHOUT built-in modulation [closed]

I'm trying to find an RF front-end module for a simple data transmission system of 500 bps. Since I'm testing different encryptions, I want to modulate the signal, encrypt it, and then transmit it. ...
5k views

### What does it mean for a signal to have an amplitude below 0 dB?

I am a software developer (using high level languages like .NET,C,C++ etc) trying to understand how computers work at a lower level. I understand that amplitude is always positive because it is ...
128 views

### Power and decibels

In one of the examples in a engineering textbook, I noticed that the decibel value for the Power of a transmitter (also known as modulator) was 20DB and this was said to be equivalent to 100W. ...
216 views

### Voltage modulation with an LDO

I am trying to build a voltage modulation circuit using an adjustable LDO and a uC switchable resistor network (to provide different Vout levels). I need the circuit to provide 4.9, 5.1 and 5.3V at ...
677 views

### What limits the modulation of digital signals?

I am trying to understand why there are different speed on different frequency bands. I see that e.g. ZigBee can do 250kb/s for both 2.4GHz and 868/915MHz, but <...
945 views

### Generate a 200kHz varying voltage signal

I have a 12V DC supply from just a normal household converter. We have to make a circuit which will output an 200kHz AC signal with a p2p voltage of 3-12 volts depending on a strain gauge. 3 being no ...
1k views

### How can I superimpose Pulse signal

I designed this circuit, put V1 as sinusoidal source and output was good at oscilloscope.However when I changed V1 to pulse signal there was no output on oscilloscope. Thanks to tell me if pulse ...
605 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 ...
230 views

### In the logarithmic compressor in PCM, which law is used in countries other than the US, Canada and European countries?

US and Canada use A-law and Europe use µ-law. I can't seem to find what India and other countries use?
383 views

### Why is RZ-DPSK more nonlinear tolerant than NRZ-DPSK?

In fiber optics, why would RZ-DPSK be more suited for long-haul transmissions over NRZ-DPSK? Is the tolerance to non-linearity due to the power intensity or something else?
5k views

### FM Transmitter Modulation

I am designing an FM transmitter as a learning experience and for fun, but I am having some difficulty with FM modulation. I am using a VCO with a Colpitts topology and common emitter configuration. ...
2k views

All radio receivers seem to use the heterodyne principle. I can see that it will be easier to work with a fixed frequency than demodulating from a wide range. Questions: what's the difference ...
66k views

### What is the basic difference between AM and FM radio?

I want to know the basic/fundamental difference between AM and FM radio. Why nowadays FM radio has replaced AM and has become more popular?