Questions tagged [modulation]

Generic term for coding information onto another carrier signal

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5answers
3k views

Why can a single sine wave signal be used to send digital data but a composite signal is needed to send human talk,etc.?

I can understand the following text (Data Communications and Networking: 4th Edition, Berhouz Forouzan, Ch.5, page 179) which says that a property of a single sine wave carrier signal (phase, ...
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3answers
2k views

FM transmitter design?

I stumbled across a relatively simple FM radio transmitter online. Credit: makezine.com I wanted to understand how it works (it is called "super simple" on the website), but several hours I have ...
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0answers
125 views

Speaker designed for ultrasound operation

I've created a transmission protocol in order to transmit information bits between a PC speaker and a smartphone, or between 2 smartphones using ultrasounds. I've implemented a QFSK system which uses ...
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1answer
738 views

What's the advantage of PAM modulation over QAM?

What are the main advantages of PAM (Pulse amplitude modulation) modulation over QAM ? Ethernet is using PAM for 1000BASET and 10GBASET, but any other high speed links use QAM like DOCSIS, ADSL/VDSL ...
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2answers
268 views

How are the original signal and the AM signal related?

Use the TIMS “Variable DC” module to generate a 1V DC signal. Use the “Adder” module to add this DC signal to the message signal generated in task 1 (this will produce the ...
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4answers
6k views

If an FM signal has different frequencies, how does the radio receive the signal in a fixed frequency?

If an FM signal has different frequencies according to the modulation, how does the radio receive the signal in a fixed frequency like 103.2 MHz?
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1answer
90 views

About the combination of two signals with capacitors

Here is a link of an article I've been reading. http://www.analoguehaven.com/moog/thereminblack/hotrod.pdf In page 4 there is a circuit schematic. Notice there is a part called variable pitch ...
3
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2answers
340 views

Orthogonal Frequency Division Multiplexing (OFDM)

I am not a professional but I'm trying to figure out how OFDM works. It is clear to me that OFDM works with closely spaced subcarriers with orthogonal frequency. Each subcarrier gets modulated with a ...
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1answer
175 views

Spread spectrum

Are Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Sequence (DSSS) modulations? I am confused because I have read that these are also used e.g. with Gaussian Frequency-Shift ...
3
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2answers
14k views

What is the required bandwidth for QAM modulation?

Why is the allocated bandwith smaller with QAM-16 or 64 compared to e.g. QAM-4? I am not a professional so I'm looking for an intuitive explanation.
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1answer
1k views

Calculating Data rate function of bandwidth and SNR

I plotted BER vs SNR for BPSK modulation in Matlab and I am given bandwidth of channel (bandlimited channel). lets say it is BW1. I would like to find the data rate based on this information. I am ...
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1answer
115 views

Channel Coding with Higher modulation

Just had a theoretical question. I'm reading a book on LTE, and I came across an introductory section that talks about using higher modulation with channel coding. I understand that usually using ...
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1answer
140 views

Estimate the bandwidth required to transmit 1Mbits/s of data using a modulation scheme which comprises 32 different frequencies and 2 amplitude levels

Estimate the bandwidth required to transmit 1Mbits/s of data using a modulation scheme which comprises 32 different frequencies and 2 amplitude levels Yes, this is a homework question that ive been ...
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2answers
102 views

Drive electo-optic modulators with FPGA

I am currently using an FPGA (Virtex II NI RIO7831R) to generate the clock for a pulse generator used to drive a Linbo3 optical phase modulator. http://www.jdsu.com/en-us/Optical-Communications/...
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1answer
45 views

How to identify when a pulsed rf supply is active

I have a signal that consists of a 13MHz RF signal inside a pulse envelope (around 100ms on, 300ms off). I want to convert this to a 0-5V pulse that will just tell me when the primary RF signal is ...
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5answers
2k views

Transmission of a digital signal over a medium

A digital signal is said to have a infinite bandwidth. If a transmission medium cannot have infinite bandwidth then how can a digital signal be transmitted over such mediums? Please correct me if I ...
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3answers
912 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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2answers
3k views

How to calculate the RMS of an AC PWM?

I am looking at a servo, which is driven by PWM. The PWM signal itself modulates NOT DC but a sine AC, so when Throttle is set to 100%, I can see a rather nicely drawn sine wave. But when Throttle is ...
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1answer
156 views

Amplitude modulation transmission distortion

I need to clarify a question. Let's say that in a wire I carry a current modulated in time so that it is an amplitude modulation of a sinusoidal carrier with a modulating sinusoidal wave. In frequency ...
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5answers
3k views

Does increasing the amplitude of a signal also increase the data rate?

I face an ambiguity when considering the carrier frequency, signal frequency, bandwidth and data rate. When I consider the Shannon formula, I wonder if increasing the transmission power also means ...
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1answer
341 views

A question related to “quadrature carrier multiplexing”

While studying 'Qaudrature carrier multiplexing', I came across these statements in my text material: "Precisely varying the phase of a high-frequency carrier sine wave in a hardware circuit ...
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1answer
891 views

Working of ring modulator

I am having trouble understanding how this ring modulator works i.e. how it multiplies the input & carrier to give us appropriate output? Any help or guide will bedeeply appreciated. Reference - ...
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1answer
310 views

In Analog to Analog conversion , why we multiply instead of adding?

When we use AM i.e Amplitude Modulation , we multiply the source signal with the carrier , My Question is , why don't we add the signals ? it would be easier to modulate and demodulate I think.
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1answer
339 views

Emulating greyscale on a 1-bit LCD

I have an LCD (the DOG-M 102x64, with a uc1701 controller) that I am driving (over SPI, but that's somewhat irrelevant) from an AVR (ATMega16 @ 8 MHz) - all in all, a fairly low spec'd screen with a ...
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1answer
827 views

How to shift signal to baseband using local oscillator frequency?

If the input to a demodulator is a signal having the spectrum shown below, how would I figure out what local oscillator frequency is required to shift the signal to baseband? Is there a formula for ...
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2answers
1k views

Space vector PWM signals

I have done few BLDC motor controllers with trapezoidal modulation and they work fine. Now i'm trying to build another one with space vector modulation but as it doesn't work well i'm getting more and ...
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1answer
1k views

Can I hard wire an IR remote directly into the receiver?

I have a IR remote control and a clock (which it is designed to control.) I would like to remove the IR LED from the remote and the sensor from the clock, and run a wire between the two (so the clock ...
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1answer
848 views

38 kHz signal arduino demodulation

I need to demodulate signal with frequency 38 kHz coming from remote controller without IR receiver. I need to demodulate it and as a result get information from it. Is there any examples of similar ...
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1answer
366 views

Radar - How to keep IF constant?

A basic block diagram for FMCW radar I will be using, modified MIT radar project: MIT block diagram I My transmit frequency is 2200-2600 MHz, my receive frequency is ~2200-2600. I want my IF ...
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1answer
66 views

Analog modulation trainer

i am making communication trainer as my FYP i am confused on analog communication module .. I have 2 options first one to make different blocks of analog like mixers, filters , amplifiers ,phase ...
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1answer
193 views

Appropriate use of the word “modulated”

I don't use the word "modulated" very much and I would like to make sure I use it correctly. The TSSP77038 IR receiver module is a device that detects infrared light turning on and off quickly at a ...
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1answer
2k views

Implementation of PSK modulation/demodulation

I want to implement a BPSK modulation/demodulation using a microcontroller (Arduino Due). The carrier signal should be at 1-50 MHz and the information rate at 300 KHz. For the sender part I would ...
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1answer
247 views

Why is there a guard band in ADSL

I recently learned about ADSL and its modulation method DMT. I know the frequency spectrum is split up into a number of orthoganally spaced bins: Voice(PSTN) - Guard Band - Upstream - Downstream ...
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1answer
129 views

FM signal example

Sorry if this question is too basic, but I'm a software engineer student who must study communication systems. I try to represent a FM signal in a graphing calculator, but I don't know why the result ...
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1answer
384 views

Amplitude Modulation Frequency

In am receivers, we detect the modulating signal by using envelope detector. So, the diode rectifies the signal, and the detected signal has doubled frequency than the original. Does this mean we will ...
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1answer
1k views

Maximum signal data rate

I have a frequency signal range from 25 Khz to 35 Khz. I know that the the minimum signal sampling to assure reconstruction of the signal from the samples is 70 Khz. Would it be correct to assume ...
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2answers
141 views

Which characteristics of a Radio signal are involved to be selected by radio receiver? [duplicate]

the radio antennas receives millions of signals. how our radio selects the appropriate signal as it's input? which characteristics of the signal are involved for this selection.
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2answers
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How does the plastic-tube inductor in this wireless transmitter work?

This single layer PCB (solder side shown here) is from an old fan remote: The inductor in the plastic tube is not connected physically to any components; however, the two loops of wire surrounding it ...
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2answers
8k views

Power efficiency of SSB-Large carrier

i was studying SSB demodulation and learned that a local carrier is added to the SSB signal to make sure that envelope detection is possible. I came across a problem to find the percentage of power ...
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2answers
70 views

frequency modulation and incoming signal selection

I have some understanding of what frequency modulation entails - it entails "adding" a new frequency to the frequency spectrum of a signal. But how, exactly, is a modulated signal selected in the ...
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2answers
2k views

How does this AM Modulator work?

I have been given a question and tasked with identifying the various components. However, this circuit doesn't really seem to make sense to me. Error: RC RE inverted simulate this circuit – ...
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1answer
438 views

Why it has used BPSK modulation after OFDM?

I am quite new to OFDM modulation. I am reading this from a tutorial. In one of its parts, for showing amplitude variation of the OFDM signals, there is a graph that has used 8 sub-carriers and BPSK ...
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1answer
947 views

How is CPM Modulation Different from PSK?

Continuous phase modulation has been described to me very similar to wikipedia's definition, which basically indicated that the CPM is different from QPSK, for example, because QPSK abruptly shifts ...
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3answers
753 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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1answer
165 views

Finding the Power developed by the Nominal Frequency in FM

Question The sinusoidal signal \$f(t) = \cos(2 \pi f_m t)\$ is applied to the input of an FM system. The corresponding modulation signal output for \$f_m = 1kHz\$, is $$Q(t)=100 \cos(2 \pi ...
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2answers
2k views

How to get BPSK data from I/Q signal

I am using AD8347(0.8 GHz to 2.7 GHz Direct Conversion Quadrature Demodulator) to demodulate a BPSK modulated carrier wave. There is no intermediate frequency used. By feeding the signal into this ...
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2answers
2k views

What happens to a DSB signal if I use an envelope detector instead of Low Pass Filter

What happens to a DSB signal Modulated signal if I use an envelope detector instead of Low Pass Filter ? I am interested in knowing how the output signals vary in case of a envelope detector. I know ...
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1answer
479 views

Why is the RC value of a demodulator near the geometric mean of the period of carrier and message signal?

The figure below is a AM demodulator. My instructor told me to chose RC so as to satisfy the following inequality Tc << RC << Tm. Where Tc is the period of the carrier wave and Tm is the ...
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1answer
155 views

Nyquist Sampling rate

We have \$z(t)=\cos(100πt)\cos^2(500πt)\$ . Find Nyquist sampling rate. Well, I know that \$f_s=2f_{max}\$. My main problem is that I am not entirely sure if I could re-write the above signal as: \$...
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2answers
65 views

Spreading vector

I am reading an article that is about CDMA. In that article I encountered a term "spreading vetor". I searched some books such as Proakis and Gallager to see what it means. I even surfed internet for ...