Questions tagged [digital-communications]

Related to all communication systems that use a given digital sequence as an interface between the source and the channel input.

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5
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1answer
1k views

Why are there so many signal grounds for PCI Express?

PCIe connections have one to two ground contacts per differential signal pair. Why is this the case? On the boards that I have been studying, all of these pins are tied together onto the same ground ...
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0answers
164 views

Calculating the frequency of CPM signal in System Generator

I have a circuit which has been designed by System Generator to be implemented on FPGA. The circuit's output is a CPM (Continuous Phase Modulation) signal in which it is apparent that its ...
2
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2answers
9k views

why when calculating rise time we use 2.2 × tau? (RC Low Pass Circuit)

I am just trying to understand why we use 2.2×Tau when calculate the rise time. I can't find a derivation anywhere, I don't understand where this 2.2 came from.
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4answers
5k views

the causes of Fading of signals

I have read about fading of signals , and I have notice that the major cause of fading is multipath , but I have ask myself , what about attenuation , noise and free space loss , all of these make the ...
0
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4answers
161 views

Why don't you ever see a “anything” over (cable type)?

Possibly an obvious answer, and I'm new to electronics. You can easily find converters that convert a specific type of signal to another cable to be decompressed on the other end (example, a VGA over ...
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3answers
121 views

the implementaion of communication systems [closed]

I wonder , Why when we study communications systems , we just study the theoretical part(Math) , and we never touch the electrical circuits that used to implements this systems , I have asked my DR. ...
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3answers
164 views

Why Direct Broadcast satellite is interrupted by climatic conditions?

Television signals received through direct satellite service are mostly interrupted by the climatic conditions. But other communication systems that uses satellites are not that much affected. Why is ...
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1answer
520 views

What is wrong with this SPI implementation

I designed a system with RaspberryPi and STM32F407's, communicating with each other via SPI interfaces. For the last 3 months, tests were OK but yesterday a RaspberryPi and 2 of STM32F407's SPI ...
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1answer
497 views

What is digital Termination and when is it used?

I have heard transmission line termination but today I came across this "Digital termination" but couldn't find out why is it used and what effect does it have on digital signals?
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4answers
513 views

Bandwidth and wire parameters

Does the physical features of a wire like surface area, length or specific resistance form any sort of limit to the bandwidth of signals that can be passed through that wire?
-2
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2answers
794 views

USB to USB data transfer using microcontroller [closed]

Is that possible that we can communicate two USBs,I mean data transfer between two USB without PC ? How we can transfer data without PC between two USBs ?So please anybody can give me some idea how ...
2
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0answers
974 views

I need to calculate the average power spectral density after passing packets through a butterworth filter using MATLAB

I am trying to generate 100 packets(row vectors each of size 8192) of random bits(1,-1),filter them using butterworth filter and then plot their average power spectral density. I have to do this using ...
3
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1answer
3k views

How to “Mirror” or “Split” bar code data scanned by one USB scanner to two computers using Y cable? [closed]

I have searched this site and many others looking for a way to "split" or mirror data from an USB device (bar code scanner) to two computers. We need to do a parallel cut-over from a legacy asset ...
0
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1answer
835 views

Digital vs Analog SNR

I am not sure why one of the advantages of Digital vs Analog communication is higher SNR? For example, when I want to transfer a 4.5v signal vs a 5v signal, how does converting these values to some ...
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2answers
400 views

Off-board SPI communication issue with ADC128S052

I seem to be having trouble with my board when it is not powered. I have a TI ADC128S02 (datasheet) acting as a slave and communicating with another master board via SPI. There are buffers on the ...
2
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2answers
1k views

RS485 + Power over twisted pairs, still need isolation?

I need to communicate with a piece of hardware on an elevator car. I have a few twisted copper pairs available, but it's not CAT5, so Ethernet is out. Instead I'd like to use RS485. I've been ...
2
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2answers
6k views

Keyes IR receiver with Arduino

I'm trying to learn how to connect an IR Receiver to an Arduino Uno. I got this IR receiver as a gift, and I'm having a hard time finding a spec. sheet anywhere online. The module looks like this: ...
9
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4answers
15k views

Difference between a bus and a wire

I have been studying buses used in communication systems. From what I read at Wikipedia, "In computer architecture, a bus (from the Latin omnibus, meaning "for all") is a communication system ...
1
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2answers
97 views

Receiving on an Induction loop

Earlier, I asked a question about an induction loop being used to transmit Wi-Fi, or internet to anybody who was in the loop. I then realized that the loop could not pick up the data for uploads, ...
3
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1answer
757 views

RS-485 / CAN signal levels

From what I know, CAN at the physical layer in the "recessive" state just lets pull-up/pull-down do the work. Does that mean the rise time is theoretical slower than a RS-485 transceiver? And about ...
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2answers
54 views

Long Wires & Digital Chips

Is there a way to send digital signals over long wires(2-3 m)? Can I use buffers to do so? Is it efficient enough.
3
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2answers
614 views

Intercept SPI of RC helicopter controller

I've got this radio communication with an RC helicopter. I found that the RX on the heli is using an AVR MCU and a CYRF6989 2.4Ghz chip to communicate with the controller of the heli and translates it ...
2
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2answers
178 views

Analog to digital converter

I have very little electrical knowledge. So here is my question. I need to test some wiring harnesses if they grouped like it should be. There is 70-80 points. differencing on the harness, these ...
2
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1answer
90 views

Multiplexing a phase shift keyed signal

There are a number of great tutorials online explaining phase shift keying as a means of digital wireless communication, but none of them seem to cover the topic of multiplexing. At first glance, it ...
3
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3answers
290 views

Are Wi-Fi 'transparent' buildings superior to antennas mounted on the exterior?

Looking in particular at wireless mesh networks in cities - is it advantageous to design a building that does not interfere with Wi-Fi (e.g. out of wood instead of steel and concrete), or would ...
1
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1answer
263 views

Voice and data through TDMA in VHF systems

In a VHF radio system using TDMA can a time slot be used to carry both voice and data bits together or is it necessary that both be transmitted in two different time slots. Also while reading an ...
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2answers
123 views

Need help with digital arithmetic

I am adding two hex numbers and determining what bits in the condition code register. The numbers I am adding are 4D (base 16) and ...
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0answers
824 views

PCIe card powered but not recognized on custom interface

I have a black magic declink mini recorder card that I am trying to recognize on a small form factor linux machine (debian 3.2.46-1 x86_64). I have made a custom interface board with what I think are ...
0
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4answers
180 views

One Channel Digital Communication

I want to setup two-way digital communication between 2 Arduinos, but I'm only allowed one wire between them. One may be "master". Are there any well known methods for synchronizing communications, ...
0
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3answers
2k views

Interleaving bytes

Can someone explain how exactly interleaving is done? Is there a way to do it? From what I understood, interleaving is transmitting only some bits of a byte for transmission, but did not exactly ...
4
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3answers
20k views

Constellations in Digital Communication

What is the intuitive way of understanding concept of constellations in digital communication? I know the Gram Schmidt Procedure, Orthonormal basis functions and how to find the constellation but just ...
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2answers
630 views

How does orthogonality of subcarriers reduce intercarrier interference?

'OFDM is a spectrally efficient version of multicarrier modulation, where the subcarriers are selected such that they are all orthogonal to one another over the symbol duration, thereby avoiding the ...
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1answer
135 views

Measuring RF transmitted Power

I am running a software radio application. I need to measure the power of transmitted ofdm signal. The issue is that FCC has regulations of -50dBM/Hz. So I understand that if i need to send a signal ...
4
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2answers
5k views

What is reference voltage in a D/A converter

When I searched on the internet what I got as an answer for the above question is that the reference voltage means the highest voltage tha D/A can output. But my lecturer at college did a calculation ...
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1answer
113 views

calculating the spectrum of digital modulation methods

I have just started studying the techniques of digital modulation. The book i am reading only has mentioned the psd of bpsk, bfsk , qpsk and msk. I would like to know, how the psd is actually ...
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2answers
389 views

Minimum tolerable signal to noise ratio in modern communication systems

What is the minimum tolerable SNR in today's (digital) communication systems for successful recovery of the message? I've heard that regular commercial systems can recover the message with a SNR as ...
4
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2answers
8k views

Why is probability theory that important to communication theory?

Since Shannon's paper Mathematical theory of communications, probability theory has played an important role on communications (digital and analog). I've been checking some course descriptions on my ...
0
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2answers
2k views

Signal to Noise ratio problem

A 200mv peak to peak sinusoidal signal is applied to an ideal 12 bit A/D converter, for which Vref(v p-p full scale) is 5v. Find signal to noise ratio. This is a problem worked out by one of my ...
6
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2answers
233 views

Help to identify unknown Sync Serial Bus

Has anyone seen a sync serial bus communication like this? Repeated Pattern : Detail of beginning : Personally, I haven't been able to figure it out myself... It seems like I2C, however: The ...
1
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1answer
939 views

I2C maximum bus speed calculation

This question is based on the Philips I2C specification UM10204.They gave (section 7.2.1, page 56) for calculating the maximum frequency of the bus: $$F_{max}=\frac{1}{T_{low(min)}+T_{high(min)}+T_{...
3
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2answers
721 views

UHF Phase Modulation

I would like to design a system that produces -10 degrees and +10 degrees phase shifts at 409.6MHz (Basically BPSK). The way I'm thinking about approaching this is by using a DDS to generate the BPSK ...
0
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1answer
102 views

About gatekeeper

"Gatekeeper" is a telecommunication term. The following paragraphs are from a technical book. My question is quite simple: is "Gatekeeper" a software or a hardware? H,323 is one of those ITU(...
15
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3answers
352 views

Communication among briefcase halves

I'm building a small laptop-ish device in a briefcase. Imagine the green wires aren't there. The LCD half lies somewhat deeper in its case than the keyboard part. For now, testing and programming, I'...
18
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2answers
14k views

transmitting 5v signal over a long cable

I'm seeking for help here as I need a reliable answer to this. I need to get an input signal (low frequency 5v digital pulse), to a micro-controller from a (...
0
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2answers
3k views

building a 900Mhz long-range data communications network

First to be clear: I am a licensed amateur radio operator with about 10 years programming experience and I took electronics in high school (2008). However I tend to stay on the soft side of things. I'...
191
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8answers
34k views

Why does USB have 4 lines instead of 3?

USB specifies 4 pins: 1. VBUS +5V 2. D- Data- 3. D+ Data+ 4. GND Ground Why is this not 3? Could the Data and Power not share a common ...
8
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3answers
833 views

Passive listening to USB communication

Is it possible to passively listen on low speed USB communication? Suppose I connect a logic analyzer to D+ or D- line, will I see a valid data?
37
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10answers
19k views

SPI or I2C: which to use for a longish bus

I'm contemplating a project that would require several AVRs talking to each other over a bus. They'd be separated by as much as 6 feet. It seems like both I2C and SPI can let a series of micros ...
35
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4answers
8k views

I2C 3.3 to 5.0 V conversion

I'm trying to interface a 3.3V I2C device to a 5V Arduino. I don't have any problem with SCL line. I can use a simple voltage divider but I have an issue with the SDA line as this is bi-directional. ...

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