# Questions tagged [telecommunication]

Use this tag for questions about communications technology and its applications.

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### Antennas for HF reception

I need to know a few things about using HF antennas with RTl SDR. Whether it's a dipole or a monopole antenna, how do I choose the wavelength for the HF antenna? The range is from 3 MHz to 30 MHz. To ...
16 views

### Why is my connection over ASDL better with a vpn?

I notice that the quality of my connection over ASDL seems better when I'm connected to a VPN. Is there any specific reason to this ?
8 views

### How to to convert LTE SIM data to eSIM (as a carrier)?

I'm running a private 4g LTE network and currently using physical SIM cards. Since I have access to all of the data on the SIM card I'm wondering how I can create an eSIM using that information? Is it ...
• 101
31 views

### Two-Ray Ground-Reflection Model: Understanding the Difference in Phase Offsets at the Receiver

Currently, I'm trying to understand the Two-Ray Ground-Reflection Model. During my research, I came across the following simplification expressing the received power as follows (taken from Wikipedia): ...
145 views

### Generating 10 GHz Frequencies with Reasonable Power Requirements

Is it possible to generate 10 GHz frequency RFs at 400 V amplitudes while only using 10-100 W order power? I tried looking up how 10s of GHz frequencies are generated online and found next to nothing ...
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1 vote
30 views

### BLE - connection Point to Point

I'm developing a IoT system, I'm thinking in implementing BLE technology, but I have an unresolved question Description of the system The system implemented will have a "line" topology, ie. ...
51 views

### Squared telecom parameters

I observe that some telecommunication parameters are squared like noise power is $σ^2=-95\text{ dBm}$, and the amplifier coefficient $η^2=20\text{ dB}$. What is the meaning of the square? Can I remove ...
1k views

### Why do we always use 3.8 x 10^(-3) value as Forward Error Correction (FEC) threshold?

When we want to calculate the bit error rate (BER) for any communication system, why do we always select the 3.8 x 10-3 value as Forward Error Correction (FEC) threshold? Couldn't another value be ...
• 121
48 views

### What is the best way to enhance an existing LTE signal on a mountain hut?

I'm traveling to a mountain hut in Austria every year which is in the middle of nowhere. If you're lucky you can sometimes get one bar and a weak Long-Term Evolution (LTE) or Edge connection for a few ...
116 views

### What are the differences between a standing wave ratio meter and a frequency counter?

Im having a hard time understanding what the differences are, I see things on google saying they are both at once and I am really confused.
86 views

### Faraday's law applied to a coil in an electromagnetic field

According to Faraday's law, we have the law: where "e" is the electromotive force which is equal to the derivative of the phase of the vector "b" through the surface s of the loop ...
1 vote
37 views

### Does channel capacity depend on the valence of the signal to be transmitted?

Say I have a channel with bandwidth W and I want to send data at a rate Rb. Do my SNR requirements vary if I use binary, quaternary, 8-ary or 16-ary signalling scheme? For example let's say I have a ...
365 views

### Rotary Phones vs Pushbutton -- why did we ever have rotary?

I remember when we first got pushbutton phones -- I would say user experience is literally ten times better -- if you used a rotary phone extensively as part of your job, you would rapidly develop a ...
• 119
142 views

### How can a screen be projected on a transparent glass?

I am building something similar to Google Glasses although not exactly that. I am trying to find a way to project my 0.96inch OLED on a glass, but it can't block the front view. What I tried to do is ...
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1 vote
74 views

### Demodulation of AM signals in radio broadcast systems

I have a question regarding the demodulation of AM signals in radio systems (like car radio). I know that in order to send the audio signal from the broadcasting station to users we need first to AM ...
• 11
117 views

### Does anybody know what this symbol is?

The last couple of weeks, I've been noticing this (wifi like) symbol next to some of my contacts in my Android phone. The symbol I am interested about is in the red circle that has the outline of the ...
• 24.2k
88 views

### Double Stub Matching Impedance

I'm trying to understand the double stub matching impedance using Smith Chart. Here is the diagram for the double stub impedance: The impedance on the right has to appear purely resistive. So ...
• 101
1 vote
47 views

### Calculate the temperature stability of wavelength demultiplexer

Hi ive been given this question: A wavelength demultiplexer (DMUX) used in a DWDM communication system has a channel spacing of 100 GHz. The operating pass band of each channel is 50 GHz. The ...
• 11
44 views

### Choosing a Project

Sorry if there’s any spelling mistake... I don't know if this is the proper place to ask, but I guess if it isn't, I'll get notified. Anyway, if it isn't, I apologize. I’m a telecommunications ...
74 views

### How to make a wireless modem using a normal Wi-Fi router and a 4g usb modem

I have a normal TP link (Model: TL-WR841N) router and an USB 4g modem. But the WIFI router does not have any USB port. I want to connect the USB modem with the router, want to share internet ...
46 views

### Ethernet extender kit claims to send data through power cables - Is this correct?

I own an ethernet extender kit which has two devices connected to mains. Its data sheet claims that the device "your homes electrical wiring to extend your broadband network anywhere in the house&...
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1 vote
104 views

### When recording VHS tapes from analogue TV back in the day, was the "Teletext" data also recorded?

Ever since I was a kid in the 1990s, I've been wondering about this. I have never been able to verify/test it in a conclusive manner. It may be almost forgotten now, but in those days, each TV channel ...
1 vote
166 views

### Mesh Wifi Router Network for a Small Village

I was wondering if its possible to create mesh network of WiFi for relatively large area? I am talking about the size of small village (~20km2). The idea is to use centralized connectivity with enough ...
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57 views

### Why radio communication was limited to military use and did not become popular with general public like cell phones have become today? [closed]

Why did no private company or government try to bring radio communications to general public like we have cell phone today? What were the hurdles and challenges?
• 99
419 views

### How were the tones for DTMF chosen?

In my limited engineering knowledge, and limited research skills, I couldn't find a complete answer for the reasoning behind the chosen tones for DTMF. I did find a hint that said something about ...
1 vote
12 views

### Monitoring Connectivity on ZigBee

I am trying to figure out some ways in which a ZigBee network can be monitored. As is the case in any network, here we have a central coordinator and several slaves joined, however, there seems to be ...
1k views

### Bandwidth vs Capacity

Two questions on wireless transmission, packed into one. First: I am confused about the meaning of the term 'Bandwidth' in a wireless transmission environment. The two most common definitions I could ...
1 vote
56 views

### How progressive scan televisions works in depth?

I'm trying to understand in depth the behavior of progressive scan TV monitors (LCD/LED - Digital Television). From what we already know, the tv's screen scans the image row by row (as rolling shutter ...
• 111
1 vote
65 views

### With the "plain old telephone system", would two neighbors be able to call each other privately?

Suppose that Joe and Sue are neighbors out on the country. The year is 1950. But it could also be 1975. Or even 1999. Even though they live next to each other, and can see each other through the ...
84 views

### How is it possible that an *undertaker* invented the automatic telephone exchange? And as early as in 1888?

Strowger, an undertaker, was motivated to invent an automatic telephone exchange after having difficulties with the local telephone operators, one of whom was the wife of a competitor. He was said ...
1 vote
184 views

### Would not a telephone call (from the late 1950s) auto-disconnect if one of the parties "closes the handle"?

In the Alfred Hitchcock Presents episode "Togeather", S03E15, at 17:17, you see a drunk man leaving a telephone without putting it on its handle, with the person he was talking to begging him to "...
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1 vote
11 views

### how to implement an encoder in matlab

How can I encode a quantized vector in matlab ? This is a part of a problem where I am asked to implement a communication block using matlab.
1 vote
40 views

### Fourier serie signal approximation

I have to approximate the red function with Fourier harmonics. I am calculating complex Ck the following way. I am not sure what to put for period - T (6 or 2pi or what?). What integral limits to ...
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1 vote
190 views

### LTE to 3G IRAT Handrover: What happens afterward

Let's say that there has been a handover from LTE to 3G of a particular UE. Once the handover is complete, the MME is no longer required to maintain the sessions/bearers that has been established for ...
• 111
1 vote
108 views

### Electronic symboles in datasheets

I found these symbols in a electronic datasheet.. Are these all logic gates? or another?
1 vote
390 views

### Is it better ASTRA 19.2°E or 28°, in central continental europe?

I'm trying to tune my satellite receiver, particularly to receive the signals of the Astra satellites, which are ASTRA 19.2E and ASTRA 2 at 28º East. Looking at the picture the signal from ASTRA 28 ...
1 vote
284 views

### Spectral Efficiency of FDD, TDD, and FD

I would like to show at high level that, in principle, the spectral efficiency (SE) of frequency division duplex (FDD) equals the SE of time division duplex (TDD) and both of them are half the SE of ...
• 111
41 views

### Non Orthogonal Multiple Acess and Channel Quality Indicator

As we know in a 4G network, the LTE give us a correlation about the SNR of user and the data rate of the user. This correlation is usually a table called Channel Quality Indicator (CQI) which is found ...
1 vote
32 views

### Mobile Frequency and Carrier Frequency not Matching

I am using a Google Nexus 6 Mobile in India with Airtel as Network Provider. Recently Airtel has upgraded their Network to 2300 Mhz 4G. Whereas Google Nexus 6 Operates on Band 3 (1800Mhz) LTE. When ...
94 views

### What is the purpose of colour code for telephone wires?

I'm trying to understand how telephone wires work. I've stumbled upon this kind of identification method with colours. I can't manage to understand the reasons why is used and if it's still common to ...
1 vote
101 views

### Material to absorb very low frequency radio

Is there any material that will absorb very low frequency radio light? I know that stealth aircraft use radar absorbant materials in their design that absorb radio light best at certain frequencies, ...
1 vote
45 views

### why can't remove the Image frequency using a band-pass filter?

why can't remove the Image frequency using a band-pass filter? I've been asked to search for the reason why we can't use BPF (band-pass filter) in order to remove the effects of the Image frequency? I'...
183 views

### Negative transmit power in dBm

I am calculating the transmit power for $K$ single antenna IoT devices in an Indoor scenario. The receiver has 64 antennas. I am trying to minimize the transmit sum-power, i.e., $\sum_k p_k$, where \$...
1 vote
22 views

### Modeling of a Wireless Channel with known BER

I have to model through software a wireless (my choice: 3g,4g, 802.11...) channel with given Bit Error Rate. I'm searching some distributions, I'm reading tons of papers but I can't find how to ...
• 111
59 views

### ADSL near end crosstalk (NEXT)

During a lecture my teacher told me that the UPSTREAM in ADSL is very much affected from near end crosstalk due to DOWNSTREAM, while DOWNSTREAM is not affected by this phenomena. This lead to the ...
235 views

### What is tonal masking?

I have checked the definition of tonal masking on Wikipedia and google but I saw the definition of sound masking and auditory masking. Auditory masking Sound masking But I want to know what ...
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65 views

### Propagation loss in USRP antenna

Problem I have two USRP antennas close to each other. I know that signal strength on the receiving end has to be at least -80 dBm. Both antennas have 2 dBi of gain. I want to compute what ...
• 121
292 views

### Tethered Balloons vs Towers for Wireless Communication

If we use tethered balloons (aerostats) with wireless gateways fitted on them (let's say for Cellular or LPWAN communication), they can provide much more coverage owing to the height they can reach (e....
• 111
1 vote