Questions tagged [modulation]

Generic term for coding information onto another carrier signal

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2answers
1k views

Why are the resistors in an AM modulator necessary?

In preparation for the amateur radio exam, I have been following the preparation course material by DJ4UF. In the section about modulation it presents this diagram of a simplified AM modulator. The ...
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0answers
31 views

Sinusoidal Pulse Width Bipolar Modulation Scheme : Harmonic Spectrum

I was reading about the SPWM Bipolar Scheme for inverters the book said that we choose the frequency modulation ratio be odd to obtain only odd harmonics. What happens if we choose the frequency ...
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1answer
97 views

LoRa modulation and chirp process clarification

I am new to LoRa and I would like to get some confusion on chirp-based modulation process clarified. I was reading the very good thread Understanding the relationship between LoRa chips, chirps, ...
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10answers
7k views

How exactly does AM/FM carry both pitch and loudness of voice?

Almost every tutorial on AM/FM modulation shows the modulating signal as something like a simple tone or continuous sine wave. Now that's easy, and for AM you just superimpose the modulating signal ...
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2answers
121 views

Converting from OOK to ASK at 433MHz

I need to convert messages sent from a device using OOK modulation to ASK so it can communicate with another device that modulates in ASK. I can't modify either of those devices. I was wondering if ...
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1answer
81 views

Generating a 10MHz modulated signal [closed]

For an application I need to generate a 10 MHz sine wave signal that is modulated with 20 KHz triangle signal. This is going to be frequency modulated. This goes into another circuit which require a ...
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3answers
1k views

Why do spectrum analyzers use envelope detectors?

Spectrum analyzers can usually be represented by the following block diagram: Before entering the video filter, the signal passes through an envelope detector. What I don't understand is why this is ...
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1answer
102 views

wifi baseband access

I've got an unusual use case (optical communications) that would benefit from access to the wifi baseband signal before it is upconverted/modulated at 2.5Ghz. However most modern wifi chips combine ...
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2answers
135 views

Understanding PLL performance: PFD output bandwidth

For an application I need to FM modulate a signal with a 10 MHz bandwidth. Due to constraints I have no control over, I have to do it in an analog way (so I can't just digitize the signal, IQ modulate,...
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1answer
56 views

Amplitude Spectrum of FM wave from Bessel First order

given the values for \$\beta=5\$, for the Bessel of the first order: \$ J_{0}(5)=-0.26, J_{1}(5)=0.34, J_{2}(5)=0.49...\$ in order to plot the amplitude spectrum of the FM wave, do you treat the ...
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1answer
168 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 ...
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3answers
226 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 (...
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1answer
66 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 ...
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1answer
82 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 ...
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1answer
184 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 ...
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0answers
41 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,...
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1answer
59 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 ...
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0answers
151 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 ...
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1answer
57 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 ...
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1answer
53 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 ...
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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 ...
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2answers
496 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
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, ...
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1answer
36 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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2answers
204 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
238 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
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, ...
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1answer
432 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
112 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
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(\...
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2answers
157 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
167 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
143 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
117 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
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 ...
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1answer
93 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
252 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
314 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
157 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
561 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
92 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
325 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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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 ...
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4answers
1k 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 ...
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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
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 ...
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1answer
99 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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1answer
113 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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2answers
111 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
429 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 ...