Questions tagged [telecommunications]

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1answer
44 views

Telephone Call and Electromagnetic Waves [on hold]

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
37 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://...
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1answer
48 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
88 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 ...
-5
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2answers
41 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
41 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
45 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
535 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
51 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
300 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
282 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
50 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
66 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
105 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 ...
1
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1answer
50 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
311 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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2answers
174 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
38 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, ...
1
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1answer
123 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
142 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
77 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 ...
-2
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1answer
139 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
390 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
308 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
160 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 ...
-5
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1answer
143 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
111 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
60 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
4k 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 ...
0
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1answer
119 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 (...
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1answer
57 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 ...
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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 ...
-2
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1answer
133 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
174 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 ...
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1answer
182 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
69 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, ...
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1answer
66 views

Delta Modulation Frequency in the Integrator

Ok guys, I can't understand a thing, I have made this circuit, that is a delta modulator: As you can see with an input of 5Vpp, in the output of the integrator I found a square wave signal, that has ...
0
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2answers
36 views

what is the performance of an OFDM system in one-path channel (Flat response channel),with no multi path propagation?

i work on modelling a OFDM system in a indoor optical wireless channel (LOS channel), since my channel is LOS there is no multi -path propagation , so the delay spread of my channel is much smaller ...
1
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1answer
387 views

Transform a sinusoidal wave into a square wave with op-amp

Ok guys, I can't understand a thing, how can I turn a sinusoidal wave into a square wave with an op-amp, for example watch this image: If you pay attention, you can see in the bottom of the image a ...
0
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1answer
436 views

What is mean by channel inversion in wireless communication

Regarding the title of the question, to my understanding, Channel Inversion means that "The transmitter adapts its power to maintain constant SIR at the receiver." It is a technique used for ...
1
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1answer
57 views

Number of point to point link

I dont know if this is unrelevant here but i wish if someone could help me . The number of point to point links required in a fully connected network for 50 entities is (a) 1250 (b) 1225 (...
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5answers
2k views

What is the difference between narrowband and wideband?

Im a bit confused between the difference of Narrowband signals and Wideband signals. Is there a specific value of bandwidth which classifies a signal into Narrowband or Wideband? What values of ...
1
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1answer
62 views

Problem understanding CDMA and W-CDMA

I found it relatively easy to understand TDMA and FDMA but I just can't figure out CDMA and W-CDMA. For CDMA I think it is something like TDMA without time slots. At transmission side you can use ...
1
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2answers
374 views

A Funny-Looking Sign Off on Television (Test Pattern Generator Image) [closed]

I came across this display on television while I visited the island of Mindanao in the Philippines in November 3, 2017. I thought this might be a sign-off display from a TV network, but I noticed that ...
1
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3answers
106 views

Wireless channel interpretation [closed]

Is there a way to estimate how fast a channel changes with respect to time in practical applications? While evaluating doppler effect for a user we use the frequency at which the channel changes. How ...
3
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1answer
968 views

SIMCOM vs UBLOX [closed]

I would like to know what are your thoughts on the following below. I am designing a GSM tracking device with a SIMCOM808 module and I am speaking to an antenna supplier that advises me to rather go ...
1
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1answer
787 views

Why the difference between the RSSI and Rx Level measurements is so big?

I'm new in Telecom. Today, I downloaded the Android APK called "Network Cell Info Lite". In my house, I got this measures: RSSI: -51 RXLEV: 60 I know this measurements represents the received ...
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0answers
47 views

Does radiation level of an antenna depend on the antenna's parameters?

I am a newbie when it comes to the theory of telecommunication. I wonder whether radiation exposure may exceed recommended safety levels after changing the antenna only? I'm asking since I've seen ...