Questions tagged [modulation]

Generic term for coding information onto another carrier signal

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574 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 ...
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1answer
5k 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, ...
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1answer
47 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, ...
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286 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 ...
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1answer
304 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 ...
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1answer
56 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, ...
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1answer
672 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 ...
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2answers
166 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 ...
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2answers
90 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(\...
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190 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-...
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3answers
187 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 ...
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0answers
152 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 ...
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2answers
126 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 ...
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1answer
2k 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 ...
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1answer
168 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 ...
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2answers
282 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, ...
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1answer
338 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?
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1answer
179 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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1answer
717 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 ...
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0answers
96 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 ...
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1answer
379 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. ...
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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 ...
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4answers
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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 ...
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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 ...
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2answers
2k 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 ...
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1answer
109 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 ...
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2answers
161 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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122 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 ...
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2answers
472 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 ...
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67 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 ...
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2answers
227 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 ...
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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?
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105 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 ...
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1answer
1k 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 "...
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178 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.
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1answer
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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 ...
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1answer
213 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 ...
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487 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 ...
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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 ...
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1answer
5k views

Relation between Signal to Noise Ratio (SNR) and Transmission Bandwidth for FM signal

I was encountered by the below question :: ...
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1answer
4k views

difference between linear modulation and non-linear modulation scheme?

As shown in title: what's the difference between linear modulation and non-linear modulation scheme? I can not find the formal definition of this. And there is a different determination for the FSK ...
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1answer
898 views

Is FM index affected by frequency multiplication?

I came across this question which goes An FM signal with modulation index mf is passed through a frequency tripler. What will be the modulation index at the output of the tripler? and according to ...
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114 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 ...
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2answers
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How is it decided what modulation is used during an 802.11 communication?

I understand, that 802.11x protocolls can use different type of modulations. BPSK, QPSK, 16-QAM, 64-QAM... I also understand that the used modulation depends on the quality of the channel, I guess on ...
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1answer
1k views

Spectrum of FM signal [closed]

I've been given a question like Draw the spectrum of FM signal with modulation index beta = 0, 1 ,2,2.5. I know that it is something related to finding bessels values of the given beta but I don't ...
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1answer
2k views

Why it is preferred to have local oscillator frequency larger than carrier frequency in superheterodyne receiver?

So to obtain intermediate frequency Fif, why it is preferred to use Flo > fc So we use this equation Fif = Flo - Fc Instead of Fif = Fc - Flo
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1answer
513 views

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) ...
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1answer
81 views

Why isn't this a right expression for FM?

Like AM that can be represented as: $$\bigl(A_c+Km(t)\bigr)cos\bigl(2\pi f_ct\bigr)$$ Here, simply the amplitude is being varied by a sinusoid. Therefore similarly, why can't FM be written as: $$...
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3answers
2k views

Modulation scheme for simple signal generator

As part of a vintage radio restoration project, I decided to build a simple signal generator for alignment. The idea was straightforward, a short distance AM transmitter with a variable carrier ...
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1answer
846 views

Phase shift between pole voltage and line-to-line voltage (3 phase)

I understand that the pole voltage phase shift is 120degrees for 3 phase and the line to line voltage is equal to the difference in 2 pole voltages. However, how do I work out the phase shift between ...

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