Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [modulation]

Generic term for coding information onto another carrier signal

1
vote
1answer
148 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 ...
0
votes
3answers
214 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 (...
0
votes
1answer
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 ...
0
votes
1answer
81 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 ...
0
votes
1answer
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 ...
0
votes
0answers
40 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,...
1
vote
1answer
55 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 ...
0
votes
0answers
134 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 ...
0
votes
1answer
56 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 ...
2
votes
1answer
51 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 ...
1
vote
1answer
97 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 ...
0
votes
2answers
456 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 ...
0
votes
1answer
3k 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, ...
0
votes
1answer
33 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, ...
0
votes
2answers
186 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 ...
0
votes
1answer
226 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 ...
0
votes
1answer
47 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, ...
0
votes
1answer
377 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 ...
1
vote
2answers
103 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 ...
2
votes
2answers
83 views

Doubt in Amplitude Modulation

I am doing a course in Communication Engineering and on reading Amplitude Modulation in my textbook I found that a typical AM is defined by the following equation; $$ s(t) = (1+k_{a}m(t))A_{m}cos(\...
6
votes
2answers
152 views

MOSFET channel length modulation - Glossing over physics

I am having trouble understanding an aspect of the channel length modulation/pinch off of MOSFETs. My current understanding (For NMOS) is that when a positive voltage is applied to the gate, the P-...
-1
votes
3answers
164 views

Is there a prefered Modulation Index with Pulse Amplitude Modulation? (PAM)

You can vary the modulation index of Pulse Analogue Modulation. For instance, the RF carrier could be 100% modulated on marks, and zero % on spaces. Or, 100% on marks, 50% on spaces. In theory you ...
1
vote
0answers
133 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 ...
0
votes
2answers
115 views

Datasheet FM Modulator

Hi I want to implement a narrowband FM transmitter and I find all features about power and noise in the FM Modulator datasheet, but nothing about bandwidth. The transmitter will work at center RF ...
2
votes
1answer
1k views

Advantages of Heterodyne vs Homodyne

What are the main advantages from a theorical point of view of a Heterodyne transmitter versus a Homodyne Transmitter? I've seen the main difference is the VCO or PLL connected to the Mixer after the ...
0
votes
1answer
81 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 ...
5
votes
2answers
235 views

Can AM and FM signals at the same frequency be separated?

Suppose one radio station emits an amplitude modulated (AM) signal at 100 MHz, and a nearby station emits a frequency modulated (FM) signal at 100 MHz. Is it possible to separate these two signals, ...
0
votes
1answer
304 views

What does “a 40 kHz wave modulate with a 1 kHz sound” mean? [closed]

what is mean when say "a 40 kHz wave modulate with a 1 kHz sound"? which of AM or FM Modulation means?
0
votes
1answer
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:/...
1
vote
1answer
526 views

Can single-sideband (SSB) be used with PSK, QAM or APSK?

I got this question while considering the Nyquist no-ISI criterion, the consequence of which is that if we send one baseband symbol every T (time) then unless the bandwidth B of the channel is at ...
2
votes
0answers
91 views

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 ...
0
votes
1answer
312 views

Why the OFDM symbol length is the total number of original modulated symbol, but not one symbol length?

Recently, I am learning the principle of OFDM, and the reference is http://defenseelectronicsmag.com/site-files/defenseelectronicsmag.com/files/archive/rfdesign.com/images/archive/0101Puegel30.pdf. ...
6
votes
4answers
2k views

What does “shift keying” mean in the context of digital modulation?

English is not my native language and I do not understand why the words "shift keying" were used to describe some types of digital modulation. What does "keying" mean in the context of signals and ...
-2
votes
4answers
996 views

Why amplitude modulation is not used for sending digital data?

It seems to me that the most simple way of modulating a digital signal is using amplitude modulation. When the signal has the amplitude 0 the bit is 0 and when the signal has some amplitude then the ...
10
votes
1answer
2k views

What could this signal at 119.9 MHz be?

I had some fun with an RTL-SDR dongle, and I noticed this weird signal with no noticeable pattern at 119.9 MHz. What's even weirder is that the signal is symmetrical. What might this be? Or is ...
1
vote
2answers
1k views

AM modulation bandpass filter?

I'm trying to do an AM modulation using band pass filter at the output the carrier is at 600 kHz and the message signal is at 1.5 kHz. To get a 100% modulation I did some calculations to get fL=598.5 ...
0
votes
1answer
96 views

Generating two signals with small difference in frequency using one oscillator

I am building a data transmitter for which I chose FSK modulation. The frequencies should be around 27 MHz. I have single crystal with 27 MHz frequency and I need to get two separate frequencies that ...
1
vote
1answer
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 ...
0
votes
1answer
94 views

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 ...
3
votes
2answers
410 views

Why is Pulse Code Modulation called 'modulation' and not 'conversion'?

Since all that a pcm accomplishes is analog to digital conversion, why is it called a modulation technique? There is a message signal but no carrier. According to my knowledge, modulation requires a ...
0
votes
2answers
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 ...
1
vote
2answers
197 views

What is the use of R5, C4, C2, R6, R5, D1 in the below amplitude modulation circuit?

the project is taken from this website for my college project http://www.instructables.com/id/Modulating-Audio-on-a-LED/ I think I have figured out function of few components but still need ...
4
votes
2answers
1k views

Is DC modulated with a sine wave actually AC?

So we have a DC level that, for example, varies between 0VDC and 10VDC in sinusoidal fashion. Is that classified as alternating current even though it does not go negative?
0
votes
2answers
97 views

Function generator for OFDM signal

I have been simulating analog circuits where the input resembles an OFDM signal, but with lower frequencies. Right now I am generating the input signal with MATLAB. I now want to have a physical ...
1
vote
1answer
733 views

How does this telephone circuit modulate the current?

I've been reading on how old landline telephones work (POTS, as they call it) and found out it's quite a bit more involved than I had expected. This circuit comes from the wikipedia article "...
0
votes
2answers
163 views

Can someone please explain how this circuit works

It's s simple transmitter for light modulating certain sound we input to it. But i can't seem to know how this modulates the input signal.
0
votes
1answer
788 views

Can you get an infrared remote's signal modulation with an Arduino?

Let me preface that I am very much an electronics noob. I am decent with programming. I have an RCA L40FHD41 HDTV that I bought in 2010. I have tried using many universal remote with this TV, but ...
2
votes
1answer
184 views

What to use as an external 100 Hz modulation source for an RF Signal Generator?

I've got an old-school HP 8656B Signal Generator, for a 433MHz RF project. Typically, I've used the internal 400Hz or 1kHz modulation but for the receiver in question I need a signal source that is ...
0
votes
0answers
273 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 ...
0
votes
2answers
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 ...