Questions tagged [telecommunications]
182 questions
20
votes
2 answers
"56k modem" found in VHF band
While scanning the VHF spectrum with a SDR USB dongle, I found something that sounded like an old 56k modem (at around 160MHz, FM modulation, Europe region).
After some research, I found out that is relatively common to broadcast digital messages…
Dino
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18
votes
3 answers
How does a UK analogue telephone detect that the caller has hung up (disconnected)?
Scenario
This is a question regarding the design of UK analogue telecommunications equipment and the consequent design impact that is necessary for a router duplicating those signals. It is asked so that I can liaise with the designers of the router…
user2834566
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16
votes
3 answers
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 transmitter. What do the symbols on the diagram mean and…
Jessica Ham
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16
votes
5 answers
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 telephony and in audio is crucial to get rid of…
user1245
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16
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3 answers
Why does WiFi have a shorter range than LTE?
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 disconnected as soon as I move slightly away, and speeds are…
ObsessionWithElectricity
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13
votes
4 answers
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?
Ben
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13
votes
5 answers
How did wireless telegraphy reach so far?
Even as far back as the early 1900s, telegrams transmitted wirelessly could reach hundreds of miles. For instance, the Titanic communicated with Canada, 400 miles away, with relatively low-powered equipment. Given that telegraphs are very simple,…
InterLinked
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8
votes
5 answers
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 provided on the same twisted pair of copper wires…
H2ONaCl
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7
votes
1 answer
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 obtained everywhere for very little, compared to…
hjf
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6
votes
2 answers
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 regulated output (48 V) with much smaller…
Divya K.S
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6
votes
4 answers
How was the first overseas phone call possible back in 1927?
I was watching the Peaky Blinders TV Series when something triggered my curiosity: If there were no satellites, nor underseas cables, how come the characters were making overseas phone calls?
After some research, I learnt that those phone calls were…
Charley R.
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4
votes
2 answers
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 a voltage source at either end.
Either party can…
Mark
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4
votes
7 answers
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 for.
As a baby boomer, I learned early that the yellow and black…
Burt_Harris
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3
votes
2 answers
How is fiber coupling achieved in communication?
Optical communication with (single-mode) fibers is widespread. Pretty much the complete internet backbone is based on it.
However, I am wondering a bit how the light is coupled into the fibers. Coupling light into a single-mode fiber is a difficult…
cakelover
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3
votes
0 answers
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 there I spotted a bundle of wires with connectors…
StayOnTarget
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