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Questions tagged [digital-modulation]

Digital modulation is encoding a data signal onto a carrier wave for transmission. There are several different methodologies for digital modultion.

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What kind of Modulation? Who transmits on 850 MHz (LTE-Uplink or GPRS?)?

Hey, I found an interesting Signal on 850MHz (in Germany). It is not symmetric and very strong (relative to many others due to bad antennas). On the right side the bandwith is permanently used, on the ...
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3answers
68 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
52 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
140 views

What device can convert (EEG) voltage data to real voltage? [closed]

I seek a device that can be programmed to output physical voltages based on a set of datapoints. For example: ...
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2answers
352 views

What's the name of signal encoding used by WS2812 LEDs? [duplicate]

The WS2812b color LED uses some kind of duty cycle encoding to encode three states: one zero reset This can be seen in the following figure: (Source: https://cpldcpu.files.wordpress.com/2014/01/...
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32 views

Delta modulation slope overloading

I have a question about a problem in a textbook I can't exactly solve. It goes as follow: Given a message m(t) as input to a DM system $$ m(t) = 3cos(890\pi t) - 0.7sin(1000\sqrt{3}t) $$ Determine ...
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2answers
53 views

Geometric representation of GMSK signal

Can anyone provide me the geometric representation of GMSK signal? Also, am I correct in saying that bit energy of GMSK is same as its symbol energy since MSK is a binary modulation scheme with only ...
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1answer
36 views

Method to find Correlation for a random variable and thereby power spectral density of random signal

I'm trying really hard to understand the segment of text from a standard communication book ( Modern digital and analog communications by B P Lathi). We are trying to find the power spectral density ...
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4answers
153 views

Phase Shift Keying: Is it ever actually used?

during my course in digital communications Phase Shift Keying is talked about where the modulation consisted of altering the phase of the carrier signal. This process takes up a lot of spectrum so I ...
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48 views

Why do we need an (adaptive) equalizer when we have a matched filter at the receiver?

When both can perform the same task of reducing the effects of ISI, why use both and not just one at the receiver end?
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2answers
53 views

In CPFSK, suppose we transmit a continuous bit stream of 1, then for how long will the frequency go on increasing?

I read something about phase memory but didn't get proper information. My specific doubt is, let's say phase memory is L, then after L '1s', will we have a phase discontinuity and will the frequency ...
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3answers
148 views

How does widening the frequency band allows us to make faster pulses in a radio link?

I’m new to radio communication and completely ignorant in the topic. I spent some time writing software which includes calculation of the channel capacity (in bits/second or symbols/second or bauds) ...
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1answer
39 views

Stability of delta sigma modulator with high frequency signal input

What happens to the high frequency part of a signal (in the region where the quantization noise is high) requantized with a delta sigma modulator, let's say with $$STF = 1$$ and $$NTF = (1-z^{-1})^N$$?...
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126 views

One-wire concept for WS2812B - adding signal onto DC

I would like to reduce the amount of lines for a string of WS2812B RGB LEDs for a project. In my understanding two lines should be sufficient, since we can modulate the signal onto the DC line. ...
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1answer
42 views

(W)CDMA, any repeating information?

I am looking to characterize a WCDMA channel to study the effects of multi-path. In order to do this I need to be able to find some repeating information (bit sequence) being transmitted by a station. ...
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2answers
1k views

Demodulate a AM signal from the carrier using Matlab

So the AM signal has a bandwidth of 5kHz and the carrier signal is 100kHz. I demodulate the AM signal by multiplying it to a sin function (sin(2000000*pi), same frequency with the carrier frequency). ...
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1answer
459 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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4answers
821 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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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 ...
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2answers
46 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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2answers
319 views

what relationships exists between the BER vs SNR graphs of QPSK and QAM modulation schemes on data throughput. which scheme does better?

Using QAM and QPSK modulation schemes, RF field measurements like received signal power and pathloss were obtained from where the SNR values were estimated. Their BER values were also calculated and ...
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3answers
357 views

Scrambler with all zeros on input

Several communications standards use LFSR-based self-synchronizing (multiplicative) scramblers that are never reset to an initial state after initial power on. For example, 10GBASE-R Ethernet ...
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2answers
507 views

“56k modem” found in VHF band

While scanning the VHF spectrum with a SDR USB dongle, I found something that sounded like an old 56k modem (at around 160MHz, FM modulation, Europe region). After some research, I found out that is ...
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75 views

How does QAM retain the phase of the signals?

QAM is a modulation technique where amplitude modulation is performed for two signals, one sine signal and another cosine signal. Since the signals are out of phase, the information in these signals ...
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222 views

Delta modulation (DM) signals

Trying to understand this circuit. Will this produce a representation similar to example in second image (if U_inf is the sine wave "original") ? Assuming that, I expect U_DM to look like the "...
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5answers
171 views

How does digital signal is propogated in channel?

As mentioned on the picture a digital signal is sent, after that it got affected by noise and disturbances and it is retrieved perfectly by the repeaters. My question is, signal in digital is sent as ...
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2answers
7k views

Understanding the relationship between LoRa chips, chirps, symbols and bits

I'm trying to understand the actual relationship between LoRa chips, "chirps", symbols and bits. I don't mean just the equations that relate the various rates, but actually how these things relate ...
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1answer
525 views

maximizing IR range and peak current

I ordered a bunch of infrared detector diodes (aka IR diode) and infrared transmitters. luckily the detectors are blue (and don't respond to normal room light). I am planning to order a bunch of ...
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1answer
426 views

How continuous phase variation is achieved in MSK scheme?

As per my knowledge MSK(minimum shift keying) is same as FSK with the modulation index of 0.5. Now I want to understand how this 0.5 modulation index helps MSK to achieve phase continuity which was ...
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1answer
49 views

Can I store all channels from the signal coming from a digital antenna? [closed]

Whatever signal comes out of a digital antenna carries many basic broadcast channels (ABC, FOX etc.) Once this signal reaches the TV, some extraction circuit extracts (or tunes to) the channel I want ...
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0answers
109 views

Showing QAM constellation diagramm on signal analyzer

I've been playing with some lab equipment recently in order to learn more about digital modulation techniques. I've connected R&S signal generator SMIQ 03B with the R&S spectrum analyzer FSIQ ...
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2k views

What is the modulation technique used in optical fiber?

Which type of modulation should be preferred for optical fiber communication and why? I read some pdf and it was mentioned that ASK,PSK etc are used but I could not identify the clear winner among ...
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3answers
419 views

How does the dish size increase reception range of radio signals?

For example if you want to transmit a song through FM, does the receiver's dish size actually increase the range in which he can detect these signals? if it does then how?
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2answers
970 views

Is it possible to visualize a 2.4 GHz digital signal without an oscilloscope?

I would like to visualize the RF signal of a 6 Channel Spektrum DX6i transmitter that operates in the 2.4 GHz band, in order to visualize changes in the signal when I move the control sticks. The Tx ...
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497 views

Envelope detector RC condition

Given that the frequency_carrier = 450kHz; The modulating signal is a triangle wave of frequency = 2kHz; Having a Capacitor = 10nF; - What should be the value of resistor in this circuit: I know ...
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1answer
559 views

How to perform FSK modulation in VHDL

FSK Modulation in VHDL Hello, I have a VHDL block that performs FSK modulation. It looks like this The operation of the VHDL block goes like this. Fsk_data selects ...
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1answer
129 views

can not comiunicate through ask rf module [closed]

I wanted to send data by ardunio through dra886tx(board on the left side ) and receive by another ardunio through dra887rx ; i don't know whats the problem but nothing happen on the receiver board ...
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1answer
288 views

What bandwidth is needed for an arbitrary digital signal?

I am building a fiber-optic data link, with a laser driver and photodiode receiver. My goal is to transmit data at 50Mbit/s. I'm looking for what bandwidth this would take. Obviously 50MHz would not ...
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1answer
62 views

Is Turbo decoding modulation dependent?

I want to use the BER result of a turbo coded system from an article, but my system is not BPSK (and the article has discussed just the BPSK case). Now I wonder is Turbo decoder, modulation dependent?
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1answer
365 views

Bit Error Probability for 8PSK

I'm trying to understand how to derive the BEP for 8PSK by geometrically looking at the decision regions. Say I have this 8PSK signal set and the corresponding decision boundaries. I assume that '...
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1answer
217 views

Simulation of BPSK in fading channels

I'm trying to simulate BPSK in a channel with Rayleigh fading and AWGN, then obtain the Bit Error Probability (BEP). My program is written in C. I compared my BEP vs \$\frac{E_b}{N_0}\$ (SNR per bit) ...
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0answers
66 views

Compressed single-sideband modulation?

I've had an idea for a new form of SSB modulation, using half-angle formulas as a basis for compressing the sideband of a SSB voice transmission. However, this idea seems so simple that I feel it must ...
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128 views

How do I get a clean PWM (Modulation) signal to my RF supply/control for my laser?

I connected a PWM signal to the MOD input for the RF power supply. On the scope, it changed from a relatively clean signal to a very noisy signal. The laser head did turn on and fire, however, the ...
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1answer
746 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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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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1answer
121 views

Digital Modulation

Hey I have an exam tomorrow and I cant work out this past question and I would appreciate any help. A black and white TV picture consists of approx. 3x10^5 elements, each of which may occupy one of ...
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1answer
1k views

What's the difference between PWM and VPW?

What's the difference between pulse-width modulation (PWM) and variable pulse width (VPW)?
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1answer
281 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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2answers
13k 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
133 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 ...