Questions tagged [modulation]

Generic term for coding information onto another carrier signal

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Foster - Seeley FM Demodulator Explanation

Consider this Foster Seeley Demodulator If I have correctly understood, its basic working principle is the fact that at the secondary coils (L2) of the Balun there will be two signals equal and ...
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2answers
55 views

Double Balanced Mixer

Consider this double balanced mixer: Its output contains only the frequencies generated by the product of those of LO and RF signals, where LO is supposed to be a large signal (which switches ON and ...
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1answer
74 views

2n7000 used for inductively coupled load modulation apparently latched

So I've got a fairly basic circuit set up for load modulation of an inductively coupled circuit: A few notes on the above: LC's were designed for 1 MHz but work better at 950 kHz, thus the chosen ...
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50 views

Bandwidth for a Butterworth filter

How to choose the bandwidth of a 2 pole Butterworth filter for QPSK modulation? What bandwidth should be chosen, if symbol duration is 10 ms? How to limit ISI for QPSK modulation?
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41 views

How to choose an antenna for an FM transmitter? [duplicate]

Ok guys I can't understand something. Say that I have this circuit: Assuming that I apply at the antenna 5V, how can I calculate how much power I will trasmit? I found on internet that the current ...
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1answer
37 views

Convering bandwidth (frequency) to bit rate without knowledge of the modulation?

How would i convert a bandwidth of say 30kHz to bps if I only know the number of bits per sample (4)? (and I was using a two chanel system). I am assuming it is simply 30KHz * 2 * 4 but this may be ...
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6answers
2k views

Why does more bandwidth guarantee high bit rate?

The definition of bandwidth is frequency range and it seems to be correct to say that higher bandwidth guarantees higher data rate. However, i do not understand why it does. Data rate depends on ...
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1answer
171 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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1answer
67 views

FSK generation with Timer 555

On the Internet I found FSK generator connection diagram. And I'm trying to connect up it in Qucs. I' sure, 555 timer is working properly. But at the output of the whole schema I get unclear result. ...
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1answer
837 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....
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1answer
30 views

Is there a difference between rise and fall time and modulation frequency

I was wondering if there was a difference between modulation frequency and rise and fall times of a laser diode or LED? If a laser had a modulation frequency of 100MHz would that be the same as a rise ...
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22 views

Bessel function normalization graph

This graph is drawn bessel function table but ı stick around reading table.Does table gives directly frequency spectrum amplitude values or only jn(ß) values?
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1answer
4k 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. ...
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3answers
900 views

An alternative way to make a VCO?

From what I am able to understand, a voltage controlled oscillator is "controlled by a voltage" when this voltage is applied to vary the value of the tank circuit: e.g. this could happen by applying ...
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1answer
424 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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0answers
20 views

Data rate with modulation and conventional encoding

I had a rather simple question. Say I had a SISO communications system with an information data rate of 50 Mbps that uses QPSK modulation and a rate 1/2 conventional coding. What would be my symbol ...
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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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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
621 views

Why do more phase shifts cause the need for higher bandwidth when Frequency Shift Keying (FSK) is used?

What I don't get is why a phase shift "decreases" the data rate and thus the need for more bandwidth to get the same throughput as without the phase shift.
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2answers
49 views

vestigial sideband modulation [closed]

If we are given the following equation of Vestigial Side-band Modulation, what values will I put in the equation? $$ H_0(f)=\frac{1}{H_i(f+f_c)+H_i(f-f_c)} $$
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1answer
90 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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1answer
22 views

prevent receiver components from interfering with output of modulator

I am working on an ASK modulator and de-modulator. The modulator works fine (thanks to great folks at SE). However when I try to pass the modulator output to the input terminal of the receiver, the ...
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2answers
73 views

ASK modulator using transistor not working properly at high frequencies

I am trying to make a simple ASK modulator circuit using an npn transistor. It works acceptably at lower frequencies. However at higher frequencies, it doesn't work properly. The amplitude of output ...
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3answers
37k 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 ...
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0answers
43 views

What effect do R5,R6,R7,R8 have on the following DSBSC Modulator?

I know that the first 741 essentially adds m(t) and c(t).The gain should be 1 so why do we have 3.9kohms resistance ? What use is it ? The second 741 circuit is a band pass filter . I think there is a ...
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17 views

Single Ended DAC to Differential Input Modulator

I'm trying to drive a differential input IQ modulator (LT5571) with a single ended DAC (MCP4912) for modulation of a narrow band signal (~10kHz max). Because of the nature of the low frequency ...
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1answer
92 views

Vibrato audio effect circuit

I would like to build a circuit that adds a "vibrato" audio effect to a simple sine wave input. Sample audio clip from Wikipedia: Vibrato, Sound Frequency 500Hz, Frequency Modulation 50Hz - Vibrato ...
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1answer
35 views

Source generator for Satellite Tuner input

I need to design a source generator for a TV factory. They want to automatize the functional tests by applying a test module to the TV's at the end of the production line. All the peripherals of the ...
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0answers
40 views

Three level PWM modulator circuit feedback simulation

I'm trying to design a three level PWM circuit with feedback and i'm struggling to understand the feedback aspect. The design is based on this design by Texas instruments and modified to suit three ...
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1answer
19 views

Conversion Gain Definition for DSB-SC Upconversion

If I multiply a baseband signal \$A cos(C\omega t)\$ and a carrier signal \$B cos(D\omega t)\$, the result is \$\frac{AB}{2} [cos(C-D)\omega t+cos(C+D)\omega t]\$, which is a double sideband, ...
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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 ...
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1answer
57 views

understanding AFSK and FSK

I’d like to understand 1200Hz/2200Hz AFSK in commonly used APRS/Packet/AX.25 applications. When I look at the datasheets for some of the chips existing projects use (e.g the Si446x transceiver-on-a-...
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26 views

Labview - Active amplifier

I need to create a pulsed current variable from 0 to 20A to run solenoid with a very low resistance. Which is the best solution for you? Right now I am trying to generate a pulsed current with ...
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2answers
21k 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 ...
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2answers
80 views

Why don't we use analog remote mics?

All remote microphones sends digital samples over the ether. Why no analog remote microphones? I know that digital signals are less sensitive to noises, but there are several advantages of analog ...
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0answers
51 views

iPhone headphone out as a signal source for AM modulation circuit

EDIT: I wonder what is the appropriate model for an iPhone/MP3 player audio out? I imagined it as a voltage source that would support whatever current the resistance it’s connected to necessitates. Is ...
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2answers
62 views

What does the phase discriminator portion of the Costas Receiver do mathematically?

What does the phase discriminator portion of the Costas Receiver do mathematically? The output of the I-channel is \$ \frac{1}{2}A_C \cos \phi m(t) \$. Which means for small deviation of phase \$ \...
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1answer
39 views

Does DSB-SC signals retain original shape of the message signal \$ x(t) \$ when \$ x(t) <0 \$?

The conventional DSB-FC AM signal is given by: \$ s(t)=[A+x(t)]\cos \omega _C t \$ In conventional DSB-FC AM we take care of the fact that \$ |x(t) | <A\$. So that the modulated signal is not ...
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3answers
120 views

How is companding different from pre-emphasis and de-emphasis?

What I know is that interference increases linearly with frequency and thus noise power is concentrated at higher frequency. So, to reduce noise, pre-emphasis and de-emphasis filters are used which ...
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1answer
129 views

How to understand this simple voice-over-laser circuit

The Sci-Toys project A simple laser communicator shows a surprisingly simple way to send an audio signal over a laser pointer. A transformer AC-couples an audio signal directly into the DC supply to ...
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3answers
737 views

How does an AM-modulated signal sound like in a speaker?

Let us compare two signals: one is a normal sinusoidal signal with single frequency 5khz with 1V amplitude (2V peak-to-peak). The other signal has a carrier frequency of 5khz and 2V peak-to-peak, but ...
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135 views

How is the power of a SSB-SC signal half that of DSB-SC signal?

Intuitively I get it that my SSB power has to be half of DSB power but mathematically I am unable to get this. Say working for tone modulation. $$m(t)=mA\cos(w_mt)$$ where m is modulation index. ...
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133 views

Amplitude modulation with diode

I was studying about amplitude modulation and I found this circuit on the internet. Does anyone know why that ground is needed? Is the first part(three resistors) an adding circuit? Does the diode ...
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2answers
144 views

Why different SFs in LoRa are said to be orthogonal?

As orthogonality is an important characteristic in LoRaWAN but most public references just make a conclusion that different SFs are orthogonal. This confused me a lot and hope to make a clear ...
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1answer
42 views

How come optical data modulation is faster than that of electrical modulation while optical modulation is done by electricity?

why optical data is of high bandwidth that that of electrical copper data bandwidth when we use electrical signal to achieve optical data modulation ?
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34 views

Modulation index and sidebands

I have built a Mach Zehnder interferometer in which a laser beam is first split. After each splitted beam is passed through a AOM driven at a fixed RF in my case 40 MHz and 40.04 MHz they are ...
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1answer
56 views

Quadrature modulation Digital to Analog

I want to use an FPGA to generate quadrature modulated signals for use with an RF transceiver (something like MAX2828 ). I am confused specifically about how the digital to analog modulation should ...
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2answers
49 views

Finding required BW with Bessel table

The FM signal (see image 1) is applied to a 50 Ohms antenna, and I am seeking the required bandwith with the Bessel table (image 2). From the FM signal, I deduced that the information frequency is ...
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1answer
219 views

FM Transmitter (Modulator) Circuit Simulation Problem [duplicate]

I've asked my question before, and I am writing this new question with some edits based on my previous problem. I am building a small FM Modulator ( Transmitting ) simulation on (Multisim). I've used ...