Questions tagged [telecommunications]

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84 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
45 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
29 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
33 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
47 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
25 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 ...
1
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1answer
42 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 <...
0
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1answer
53 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
58 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 ...
15
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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 ...
1
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2answers
72 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
55 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, ...
0
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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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0answers
38 views

Need help in computing the evolution of symbol error rate for uncoded OOK scheme over fading channels

I am trying to reproduce the results exhibited in Fig. 1. in the reference, i.e., "Error performance of coded FSO links in turbulent atmosphere modeled by gamma-gamma distributions" linked to (https://...
0
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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 ...
0
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2answers
96 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 ...
0
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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 ...
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2answers
56 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
43 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 ...
0
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1answer
60 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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0answers
21 views

calculating the probability of a successful broadcast in p-csma protocol

am quite unsure with the following question. would appreciate your help with it: in a 3 stationed p-csma network, where \$p=0.3\$, we know that in \$t_0\$ the network is restarted, the channel is ...
7
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1answer
545 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 ...
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0answers
53 views

a tricky question regarding CDMA with 4 stations

i have encountered this tricky questions that left me really confused, would really appreciate your insight regarding it: given a cellular system with four stations that utilizes CDMA. given the ...
2
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1answer
335 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 ...
2
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2answers
414 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
74 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 ...
0
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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
111 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
73 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
474 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
195 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
393 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
151 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 ...
1
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1answer
87 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
145 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 ...
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5answers
480 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?
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1answer
371 views

Why microwave links on cell towers have high frequency?

Why microwave links are in the higher microwave spectrum (I don't know exactly but I guess it's around 20-40GHz). If by Friis Equation higher frequencies have lower range then why use higher frequency ...
1
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1answer
161 views

How can a phone transmit the signal back to tower? [closed]

If cellphones have such a low power transmitter (around 200mW for LTE) and also doesn't have directionality then how can they talk back to the tower even though they are so powerful and built ...
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1answer
147 views

Do the FCC's regulations make any sense?

I have read on the following page that the maximum permissible exposure MPE standard FCC have is 1 mW/cm2 for RF wave above 1500 MHz for general population. http://www.rfcafe.com/references/electrical/...
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2answers
113 views

Why FM has larger range than cellular network [closed]

I can receive FM signal about 50km away from the transmitting station but I lose signal from cell towers in about few km (1-3km)
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1answer
61 views

How cell sites work? [closed]

In Mobile communication, how do cell sites communicate to each other to the point when they reach the cell site which is connected to the other mobile phone when I make a call . What is the medium of ...
15
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3answers
5k views

Why does WiFi have a shorter range than LTE? [closed]

It seems confusing that my phone receives -87 dbm LTE signal and shows a full 4 bars with the speeds of UPLOAD: 20Mbps DOWNLOAD:13.6Mbps But my WiFi is showing 1 bar at -89 dbm and I get ...
1
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1answer
137 views

How can a pringles can act as WiFi booster? [closed]

How does a wifi transciever placed inside a Pringles can act as a wifi signal booster. I saw this trick on Mr robot TV series. Do WiFi routers emit less power than GSM or LTE. I know for : GSM - 2W (...
0
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1answer
58 views

Meaning of Evolution in LTE (Long-Term Evolution)

The term Evolution/Evolved (E) is everywhere in communications, and simply put i don't understand why. The answer I am looking for is one that will help me know what meaning i should associate with ...
1
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1answer
46 views

Decide coherent time and fade duration through empirical studies on the channel and relate them to channel modeling

I. Scenario: TX floating in the lossy heterogeneous medium with undetermined positions within a limited region; RX fixed in the air and closed to the boundary of air-lossy medium; Frequency: 500 MHz ...
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1answer
149 views

How does cellphone idle time work?

Imagine a basic cell phone which operates in only 2G network and able to provide voice call & SMS service. Does this cell phone transmit any data to BTS in idle time (that is when the cell phone ...
0
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1answer
206 views

Xbee pro s2c 2.4 ghz 10dbi Antenna and its effect

Just wondreing how to increase the range/distance of communication between two xbee modules operating in API mode, we are considering to replace the 2.4 ghz antenna of 5dbi gain with 10dbi high gain ...
1
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1answer
225 views

What is the difference between SNR of a wideband system and the SNR for a narrowband system

I was reading Wireless Communications by Andrea Goldsmith in the book the author has stated that the Noise power for a wideband system with Bandwidth B is (B*N/2). Could someone help me understand why ...
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0answers
72 views

20 mA current loop speed/distance trade offs?

By 20 mA current loop, I'm referring to digital current loop communications, e.g. the standard used by old Model 33 teletypes. (Image credit: By Rama & Musée Bolo - Own work, CC BY-SA 2.0 fr, ...