Questions tagged [telecommunications]

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Why are microwaves unidirectional and radio waves omnidirectional?

I understand that any wave can be given direction using a setup like a phased array. As I read about the properties of EM waves, I find that microwaves are unidirectional in nature. What is it about ...
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How can the Earth be used as a return path? Wouldn't the signal just dissipate after reaching the destination?

I was reading an academic document and I came across this statement: Telegraphy, 1747 (a singe-wire line with the Earth as a return conductor – the first transmission line) I can't imagine how that ...
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1 answer
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Hamming code error correction multiple bits

If we send a message from a sender and the noisy channel produces 2 bits with error can we detect both bits using hamming code or is it just for 1 bit?
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6 votes
2 answers
1k views

Why is the telecom input power supply range 36 to 72 V (polarity ignored)?

Why is the telecom power supply voltage level specifieded with a wide range: 36 to 72 V? Is it because the rectified AC voltage would have variations as per AC line variations? We could easily get a ...
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Questions about understanding networks (Telecommunications eng)

So I read about Network topology, about typs of communications like ptp, ptmp, mptmp and about Addressing methods (multicasting, broadcasting), etc... I'm very confused. What is the difference between ...
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1 vote
1 answer
71 views

How to convert data signal line coding from RZ to NRZ?

I have a user data stream at 10 kbps and line coded as uni-polar, 0-5 Volts, RZ (return to zero). What methods are there to convert this signal to an NRZ (non return to zero) format? The only way I ...
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1 vote
0 answers
54 views

How should I understand this interpretation?

Studying spatial diversity in telecommunication engineering (Fundamentals of Wireless Communication, D. Tse and P. Viswannath), I read this paragraph. $${\text {In}}\,{\|}{\textbf h}{\|}^{2}{\text {...
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Can I reconstruct the channel impulse response from OFDM least square channel estimation?

I'm working on a successive interference cancellation (SIC) project for an OFDM system. I used pilots and least square channel estimation to estimate the channel frequency response (CFR.) It works ...
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How to do a comparative analysis of electrical characteristics of two 134kHz RFID circuits?

In the figure below there are two antenna circuits, both are circuits used in RFID at 134kHz, which are external to the TMS3705 IC. Circuit number 1 is an old circuit, circuit number 2 is the circuit ...
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Find Bps given a star graph

Today I wrote finals for the semester in the subject "Introduction to Telecommunications".1 question was like this: Suppose we have a star graph with 64 dots in it.That would mean we are ...
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1 answer
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How to switch off the CATV signal on a splitter port

I'm trying to create some automation of switching off the CATV signal on a splitter port. Using a regular 5V Arduino relay module I've tried to interrupt the wire from the center of the coaxial cable ...
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-3 votes
2 answers
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5G and aircraft? [closed]

I just read the statement of a company, "We are frustrated by the FAA’s inability to do what nearly 40 countries have done, which is to safely deploy 5G technology without disrupting aviation ...
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Optical Receivers and Amplifiers

I have been doing some past papers for a university module I am studying. I am not from an electrical engineering background so don’t really know how to attempt the question attached. I would really ...
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10 votes
4 answers
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What is the purpose of a carrier signal in communication technology?

What is the carrier signal for when we actually do not care about this but only about the other signal (the useful signal?) Why isn't only the useful signal used instead of mixing it with the carrier?...
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2 votes
0 answers
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Identify this telephony or data connector?

Recently I had the opportunity to visit a telecom/data room that was being decommissioned. A lot of the remaining equipment seemed to be from around year 2000 or so, as best as I could tell. While ...
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LTE Bandwidth at band edge

If my LTE uplink channel is right on the band 20 edge for example 861.9MHz or 24449 EARFCN and my LTE BW is 10MHz does that mean the final signal would be outside of B20 or 856.9-866.9 ? Or is the ...
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2 votes
1 answer
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How are simultaneous transmissions decoded at the receiver?

I am finding it hard to understand how does a receiver differentiate between the interference and the signal intended for the corresponding receiver. For example in a case where two user pairs are ...
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1 vote
3 answers
119 views

Manchester and NRZ coding schemes

How does NRZ recover the clock? For example, Manchester coding is a self-time scheme, but we still need to have DLL or PLL for the recovery, it can be done without those CDR circuits? and back to NRZ, ...
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How does this condition of threshold voltage come into picture in the given context?

I have been studying communication systems from a particular set of notes which I found online. The link to the notes is attached in references. In the page 56 of the PDF of notes, a statement with an ...
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16 votes
3 answers
1k views

What is this circuit diagram found on an FM transmitter?

This is the circuit diagram on the transmitter at a local FM radio station I clean at (I'm a janitor,) but I'm also studying electrical engineering. I'm puzzled by the circuit diagram on the ...
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1 vote
0 answers
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How to find priori information in Cramer Rao Lower Bound when the pdf of the parameter is unkown

In order to compute a Bayesian Cramer Rao Lower bound, we need to find the prior information of a random parameter "theta" which is a complex scalar parameter. The pdf of "theta" ...
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1 answer
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What is 'mis-registration' and 'mis-collimation' of television signals?

I was reading about early televisions and television cameras, and I came across these terms with no explanation.... They appear on Google on a few pages, but again I cannot find a definition....
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0 votes
1 answer
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NOAA satellite RF superhet receiver - local oscillator frequency precision

I am currently designing a RF receiver for the APT protocol in order to collect NOAA weather images. This has been widely done on the internet, but I'd like to do it from scratch and not use any SDR. ...
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-1 votes
2 answers
368 views

Dwell time in wireless communication

In wireless communication dwell time is defined as the amount of time a device uses a particular channel. If we take the case of a ...
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2 answers
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What does GSM 900/1800 mean?

I was looking at old Nokia 3310 phones, which have GSM 900/1800. I did some research online from a government website, along with some Google searches, to understand what GSM 900/1800 means. I got a ...
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8 votes
5 answers
4k views

Was the last mile copper wire not the limitation in dial-up internet service?

My local internet service providers can provide ADSL (asymmetric digital subscriber line) service at various speeds, for example, 50 M bits per second. This service is in Canada. Is this typically ...
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4 votes
2 answers
466 views

Modeling bidirectional communication across a coax?

I was reading about the history of cable internet and I'm interested in a simple model of full-duplex communications across a single coaxial cable. My first attempt is simply a transmission line with ...
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1 answer
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Amplitude Modulation Equation (sine or cosine)

I got an exam tomorrow and I'm still confused with something. I'm sure most people are familiar with the general equation of Amplitude Modulation. AM(t) = (Ac+m(t))cos ωc t I found that there is ...
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4 votes
7 answers
2k views

What do you call the yellow and black conductors in domestic telephone wire?

Any wannabe telco guy can tell you that the green and red pair are called "tip" and "ring" respectively, most can tell you the historical reason why. That's not what I'm looking ...
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0 votes
3 answers
123 views

Why are power losses in fiber-optical cables so high?

Suppose we have two arbitrary points A and B. Transmission between these points is over optical-fiber. We don´t care the wavelength, distance and other stuff. Now suppose we have total attenuation of ...
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1 answer
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Transmission Lines:Standaing Wave Voltage Characteristic at Half Wavelength

The voltage equation for lossless transmission line that my professor has given me is : $$V(l)=V^+ e^{j\beta l} +V^- e^{-j\beta l}$$ and he says that when singals transits by half the wavelength the ...
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1 answer
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Amplifier gain in budget links

How does an engineer calculate the required power/low-noise amplifier gain after she/he is provided with the link budget of the system?
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75 views

Why are two capacitors used in capacitive wireless power transfer instead of one?

I am an engineering student. I am studying wireless power transfer (WPT) theory. I understand that from a theoretical point of view it is possible to do capacitive wireless power transfer using a ...
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2 votes
2 answers
115 views

Is it safe to wire a telephone to a breadboard?

I am trying to connect a hardwired 2554 telephone set. There's only a few inches of slack wire coming out of the phone since it appears it was just cut there. I managed to get about half an inch of ...
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0 votes
1 answer
213 views

Difference between Li2YCY and LiYCY

I would like to ask about the difference between Li2YCY and LiYCY TP cables. As far as I know, the main difference is that the Li2YCY has core insulation based on PE and wrapped screening made from ...
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0 votes
0 answers
96 views

Why does a phase shift happen in the demodulated AM signal using envelope detection?

I was studying AM signal demodulation using envelope detection with the circuit shown below. In the book it says the low pass filter part is called a post-detection filter and that this filter causes ...
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3 votes
2 answers
502 views

What makes RF transmission so efficient?

I'm a layman in this field. I have a question about RF transmission. How does the data transferred by RF waves (for example in mobiles, wifi) reach the users accurately in spite of losses during ...
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0 votes
0 answers
114 views

Ethernet communications bypass Relay specs question

EDIT: Added another diagram to help understand that if a daisy chained device looses power, that the signal relay with power would use the normally open contacts with the device still being able to ...
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0 votes
1 answer
297 views

Is GSM full-duplex?

GSM uses FDD (frequency division duplexing) and provides separate channels for uplink and downlink. I found however, in this link, that the mobile station does not receive and transmit at the same ...
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0 answers
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Implementation of polar RZ line coding

I am teaching a course in digital communication and I want to show students how different line coding schemes are implemented in Hardware. For codes like NRZ-L, NRZ-I, manchester, I found circuits ...
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1 answer
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CDMA in FHSS system

I am having difficulty finding information about how is CDMA used in a FHSS system. In wikipedia, it mentions: FHSS is used to avoid interference, to prevent eavesdropping, and to enable code-...
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1 vote
1 answer
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How to pick an amplifier for very fast transient signals?

I'm coming to this with a Physics background. I work in solar cells. I would like to flash the solar cell with a laser and measure the voltage response. The University has a spare 10 GSPS (gigasamples ...
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0 answers
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Decode a WCDMA signal

I am trying to decode a WCDMA signal on MATLAB and I am having some trouble trying to grasp the concept of it and was hoping for some feedback. I have a row vector, 'scrambleCode,' containing 38400 ...
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1 vote
1 answer
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Nearby jail's signal jammer affecting cellphone and devices using 2.4GHz band

I just rented an apartment that seemed perfect at the first sight. However, once I moved in, I noticed a lot of instability on my cellphone signal. I found that odd, so I did some research and ...
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-1 votes
1 answer
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What is the benefit of dual polarization in radio communication?

Why are some PtP antennas and radio units connected by two feed lines -- one for horizontal polarization and one for vertical polarization? I know the difference is in the orientation of the electric ...
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0 answers
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Help identifying mysterious communications tower

There's a tower near my house that I thought was a cell tower, but I noticed it's not registered on the FCC map. Can anyone help me ID what type of tower this might be? I was thinking it was a ...
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2 votes
1 answer
871 views

Finding upper cutoff and lower cutoff frequencies on notch circuit

I need to find upper cutoff (UCF) and lower cutoff (LCF) frequencies based on formulas of a notch circuit, but I'm getting a quadratic equation (as expected) with an imaginary number (IN; not expected....
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1 vote
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Leaky Bucket Example

I have an image below of a leaky bucket image that I am trying to understand for my telecommunications class, and I was hoping for some guidance/verification if my train of thought is on the right ...
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How can one compare resonant and non resonant antenna based on parameters like Directivity, Radiation resistance, Cross polarisation, Efficiency?

Basically I want to make a choice between two antennas when ample space is given objectively based on parameters 1.Directivity 2.Radiation Resistance 3.Cross Polarization ratio 4.Loss resistance I'll ...
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2 votes
1 answer
1k views

What is difference between resonant and non resonant antennas?

I don't know if it's right place to ask it, but I searched google and books the answer I get seems to be like resonant antenna have small bandwidth and have standing wave instead non resonant antennas ...
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