Questions tagged [telecommunications]

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1answer
20 views

Calculating link budget

I was reading and found that there are different ways to calculate "link budget" and I want to know which one is correct because they are confusing to me. For example, some sources state ...
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1answer
53 views

How are LAN routers, WAN routers and eNodeBs connected to each other (TCP/IP)? [closed]

I'm new to telecommunication, and from what I understand, an user equipement is either connected to a LAN router or an eNodeB, and a LAN router is connected to a WAN router, and routers send the ...
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2answers
129 views

What are the units used in Shannon formula calculation?

I'm a CompSci student with absolutely no background in wireless communication who recently needs to do something with the Shannon formula: $$ R = W log_2\bigg(1+\frac{P_t H^2}{N_0 W}\bigg) $$ I need ...
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1answer
26 views

Equivalent baseband communication channel

I was reading on my lecture slides (I do not put them here since they are not in English) this statement about equivalent baseband channel models: In typical wireless applications, communication ...
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0answers
24 views

Which RF technology can be used between GNSS-based base and rover module?

I am looking for an RF technology/module/modem that is used to send RTK RTCM data from GNSS-based base module, to GNSS-based rover module (one way communication). I have few criteria to be considered ...
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1answer
36 views

why base stations have 2 receiving antenna and only one transmitter?

I read that a base station is divided up into sectors to accommodate multiple service providers on a single tower. why each sector has two receiving antennas and only one transmitting antenna, As we ...
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1answer
30 views

Understanding OSI Communication Model in Hardware

I have gone through the OSI communication model and the associated levels. But I do not understand on how is this implemented in the Hardware level. Or let me put it like this. Suppose we have a ...
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1answer
38 views

What is the relation between bandwidth and data rate?

If I have a 20Mhz bandwidth provided by my 2.4ghz router then will my internet speed will be 20M symbols per sec which is equal to 20×4= 80Mbps (considering 16 qam modulator with 4 bits per symbol) Is ...
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2answers
67 views

How do we separate source signals in spread spectrum?

In a point-to-point mode, that is, one transmitter and one receiver, I understand how a spread spectrum receiver can read the transmitted signal from a spread spectrum transmitter by knowing the code. ...
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0answers
20 views

Is \$ H\left\{x_h(t)\right\} = H\left\{x\left(t-\frac{\pi}{2w_c}\right)\right\} \$ where \$H\$ is Hilbert transform

Accordind to my understanding of the following: $$H\left\{X(f)\right\} = -j\;sgn(f)\; X(f) \qquad(1)$$ my work so far: since \$ x_h(t) = x\left(t-\frac{\pi}{2w_c}\right)\$, Their Hilbert ...
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0answers
15 views

Do all random access procedures and packet transmission in NB-IoT happen during one Nprach-periodicity?

I have two questions about random access procedures of NB-IoT In NB-IoT, Nprach-Periodicity is the amount of time between two consecutive random access transmission attempts. Random Access procedures ...
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1answer
44 views

Calculate power of an LTE Signal

I am looking for the formula to convert the power level of an OFDM RF signal to an absolute power level. For example if I have my typical rectangular RF spectrum and the bandwidth of the signal is ...
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1answer
35 views

Do pieces of wire or metal in general affect the inside of a Faraday cage

Building a Faraday cage and wanted to know do the dozens of metal staples and several small pieces of wire have any effect in terms of acting as an antenna?
3
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1answer
118 views

Why use both high side and low Side diode-ORs for redundant power?

This question is in regards to an example application circuit that appears in the Linear Technology / Analog datasheet for the LTC4355, and is discussed in this article. The circuit uses ideal diode ...
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1answer
66 views

How could a digital multiplexer transmit at a rate higher than its input?

From Wikipedia, "a multiplexer, also known as data selector, is a device that selects between several analog or digital inputs and forwards it to a single output line." https://en.wikipedia.org/wiki/...
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0answers
110 views

What’s this slim rectangular box on my utility pole?

It’s the silver box on the utility pole here:
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0answers
99 views

Why are tv aerial cables so mysteriously sensitive to their positioning and the proximity of people?

Digital TV Reception is not great in our area and sometimes we lose reception when conditions aren't favourable. Being UK Freeview, I'm pretty sure it uses the DVB-T2 standard. Anyway, when ...
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2answers
59 views

What is the price of increasing the QAM number?

In a QAM modulation scheme, you have a certain number of possible states which have different amplitudes/phases (like 4-QAM, 16-QAM). If you increase the number, for example switch from 16-QAM to 64-...
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2answers
30 views

Compatibilty between GPRS and LTE modules and networks [closed]

I summerized the question for ease as follows: Lets say we have an LTE module under the coverage of an old base station like 2G with GPRS. Will the LTE module work? Lets say we have a GPRS module ...
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0answers
34 views

Why does multipath impulse response contains a complex phase shift?

The multipath impulse response is defined as $$h(t) = \sum_{n=0}^{N-1} A_n e^{j\phi_n}\delta(t-\tau_n)$$ My qustion is, from intuitive point of view, why is there a complex phase change of the ...
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1answer
144 views

Guard Band Reduction in 5G compared to 4G

Why is there less guard band required for 5G as compared to 4G .For 4G guard band are defined to be 10% of bandwidth on each side while guard band for 5G are defined in 3GPP 38.101-2. For ex If we ...
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1answer
28 views

Gaussian Channel: Capacity and Explanation

Let's consider a gaussian communication channel, which is represented through this scheme: Starting by this assumption it is possible to prove that the channel capacity is equal to The computation ...
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1answer
66 views

First bit of NRZI

I was searching for Non-Return-to-Zero Inverted, but no references I couldn't find any reference about the first bit in NRZI. I know that, in NRZI, 1 refers to <...
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1answer
56 views

CDMA basic working principle

I find it hard to find on the internet a simplified explanation of the principle of operation of the CDMA system. Could you give me an example of how it works and how a receiver can correctly identify ...
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1answer
60 views

Shannon - Hartley Theorem

Let's consider the Shannon - Hartley formula for the channel capacity \$C\$: $$C = B \log_2 (1 + S/N)$$ I have two doubts about it: 1) is it correct for TDMA, FDMA, or CDMA? And why? 2) Can a ...
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5answers
3k views

How are unbalanced coaxial cables used for broadcasting TV signals without any problems?

As far as I know, in telephony STP or twisted pair cables are used. This creates balanced line impedances which is useful to mitigate for common mode related interference. So using balanced cables in ...
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2answers
192 views

Is there any relation between LJU (Line Jack Unit) and broadband speed? [closed]

My question is about LJU (Line Jack Unit) aka Rosette. I am having BSNL (service provider company) copper line broadband in India. In spite of having wired broadband, I get speeds of 6Mbps(download)...
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1answer
67 views

Grounding for surge protection for telephone/internet/data lines

After my router broke in a thunderstrorm, I am trying to establish surge protection for power lines as well as (this question) for telephone/internet lines. I found devices such as Tupavco TP302, ...
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1answer
49 views

Telephone Call and Electromagnetic Waves [closed]

Can you give me a simple explanation of how do telephone calls work? I know that when I receive a telephone call, it means that my mobile has just received a certain Electromagnetic field. But in air ...
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1answer
57 views

Radiofrequency exposure from portable (vehicle-mounted) satellite uplink antennas

I came across these broadcasting vans recently in London. The antenna that's deployed I think is a Vislink Advent uplink antenna, similar to this model, designed to transmit to satellites for ...
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2answers
98 views

What misconception about telephone circuits are they trying to address?

I'm reading a book called "Telephony" published in 1905 (Miller,Mcmeen). The book starts with this quote: To properly understand the manner in which sound is transmitted from one end of an ...
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1answer
103 views

Is an FPGA the best tool to generate a continuous flow of square pulses with arbitrary amplitude?

I need to generate a train of rectangular pulses, with positive and negative arbitrary amplitude. Ideally, I would like to have the generation electronics connected with a computer, and I would like ...
-4
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2answers
71 views

How does line encoding relate to bus protocols like SPI, serial, i2C, ethernet etc [closed]

I'm referring to line codes like bipolar, machester, miller etc... https://en.m.wikipedia.org/wiki/Line_code How do these line codes relate to bus protocols? Is it another level down? Is it ...
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0answers
54 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
78 views

Can I use a Ku band satellite dish for Wi-Fi?

Satellite TV works at 18-24Ghz and WiFi at 2.4Ghz, will a T.V dish antenna work for WiFi? Diameter of the dish is about 60-90cm
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1answer
549 views

Why did CATV standarize in 75 ohms and everyone else in 50?

All of the CATV industry runs on 75 ohm systems, while most of the rest of the radio world uses 50 ohms. Why was this standard chosen? I was wondering this because good quality RG6 cable can be ...
2
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1answer
338 views

(Textbook error?) Nyquist's relation: telegraph speed of transmission

An Introduction to Information Theory: Symbols, Signals and Noise, by John R. Pierce, says the following: In 1917, Harry Nyquist came to the American Telephone and Telegraph Company immediately after ...
2
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3answers
792 views

(When) Can I use Cat5e wiring to carry a POTS signal to a DSL modem?

According to this answer by @asndre, It is very bad idea to use Cat5e-based wiring/cabling to establish a xDSL connection. However, my telephone/internet provider technician recommended -- and ...
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2answers
107 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
67 views

Is it possible to generate user-defined signal using an android phone?

Is it possible to generate an electronic wave signal using an android phone? (Theorically) For example by customizing the firmware can I produce some signals like \$ f(t)=2 \sin 3.2×10^9t+3\cos 5×10^...
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2answers
113 views

Maximum rate Shanon Hartley

i am reading computer networks and i am trying to solve an excercise. the excercise is What is the theoretically the maximum rate at which data can be transmitted to a 4000Hz bandwidth ...
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1answer
88 views

Difference between a flared and not flared rectangular waveguide antenna

Someone can explain to me the difference in terms of performance between a flared rectangular waveguide antenna (precisely a pyramidal horn) and a not flared rectangular waveguide antenna? In horn ...
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1answer
672 views

Bandwidth-Noise-SNR relationship

Let’s say we have the noise figure F of a system of devices. We also have the bandwidth improvement coefficient ( as defined by my teacher ) $$BI=10log(\frac{B_{in}}{B_{out}})$$ where B1 is the ...
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1answer
214 views

Why aren't tethered balloons used instead of Cellphone towers? [closed]

If we use tethered balloons with wireless gateways fitted on them (let's say for Cellular or LPWAN communication), they can provide much more coverage. Why aren't they used then? While there are many ...
0
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1answer
46 views

How can Erlang C values be greater than one?

Here is an Erlang C plot I did myself. The x-axis represents the total traffic while the y-axis represents the probability. Each line represents a different total number of channels. As you can see, ...
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1answer
1k views

Why are Erlang B and Erlang C formulas different?

Erlang B determines the probability that a call is blocked and is defined as: $$Pr[blocking]= {{A^C \over C!} \over {\sum_{k = 0}^{C} {A^k \over k!}}}$$ while Erlang C determines the probability ...
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4answers
165 views

TDMA in telephone circuit switching - isn't there delay in transmitting a particular user's speech? [closed]

Let's do a simple case on the left with X and A user telephones. So the way an analog signal (user's speech X) is handled, is that it is sampled at 8000 bits / sec. The high-speed C-channel has 128 ...
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1answer
101 views

Some sort of Sim card in Fax machine

I took apart our old Fax machine. And I found some weird Sim Card (See size compared to a regular sim card). I wonder what such a card is doing in a fax machine. Also I'm wondering what else I could ...
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1answer
164 views

What is needed link budget? [closed]

Assuming I want to send a signal 1 km away from a 2.4 GHz antenna with 5 DBI gain and recieving antenna of 2.15 DBI gain. What is the minimum needed power at the receiver (not the minimum transmitter ...
0
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5answers
698 views

Why are cell towers so high? [closed]

Why do cell towers need so much height? Does the height increase antenna gain because it may provide directionality?