Electrical Engineering Stack Exchange
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Questions tagged [telephone]

A telephone, is a telecommunications device that converts sound into electronic signals suitable for transmission via cables

A telephone, or phone, is a telecommunications device that converts sound into electronic signals suitable for transmission via cables or other transmission media over long distances. First patented in 1876 by Alexander Graham Bell and further developed by many others, the telephone was the first device in human history that enabled people to talk directly with each other across large distances. It rapidly became indispensable to businesses, government, and households, and it is now among the most widely used appliances in the developed world. The word telephone has been adapted into the vocabulary of many languages. It is derived from the Greek: τῆλε, tēle, far and φωνή, phōnē, voice, together meaning distant voice.

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Why do PBX systems use -48 V?

It seems common that PBX and other telephone hardware use a positive-ground power supply, where the "hot" line is at -48v. What's the reason for that?
Carl Raymond
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Question about old telephones (late 70's - early 80's)

This question refers to old landline telephones that would have been used in households in Sweden in the late 70's and early 80's. I would think that this was probably similar to phone technology used elsewhere during that time period (except maybe…
x457812
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Disable ring on land line phones

Years ago I bought a device at Radio Shack that disabled ringing on household phones. It was a very small box with a modular receptacle on one side, a pigtail on the other with a modular plug, and a switch on the box. The switch was "ring on" and…
Roger
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Testing a phone cable length

This story must be quite familiar: From the start, I've had a problem with my phone/ADSL line: Cracks, hisses and other noise on the phone - enough to make it occasionally unusable, along with an ADSL connection that is slow and as far from reliable…
thkala
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Extracting speaker, microphone and hook signals from a two-line telephone

My aim I'd like to use a 'normal' telephone as an audio and switch interface for a project. I want to design a circuit that has the telephone A and B wires on one side (ie. an RJ-11 socket) and has four connections for my other work on the…
JP.
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Is telephone and LAN wiring symmetrical?

Is telephone and 10/100 MBps LAN wiring electrically symmetrical? I mean is it allowed to swap wires in the pairs, or is one of them like GND so they cannot be swapped? It's important to know when I plan longer wires if I can use just two wires of…
Al Kepp
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Need help improving the Caller ID FSK demodulation circuit

I have a project for which I need to be able to read Caller ID from the telephone line. I found MT88E43B chip that does FSK demodulation. They have an application circuit in their datasheet (specifically page 15, Figure 11). I have assembled…
zysoft
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Three-wire old phone to RJ11

I'm trying to connect an old phone's three wires (white, red, green) to my home line VOIP-4-wire (black, red, green, yellow) but I don't know where or what to connect. I have read this: How to Rewire a Vintage Phone so it works Today! Is it…
jminhal
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Convert 60V AC 50Hz to 60V AC 25Hz

The setup is a 240V 50Hz AC transformer outputting 60V 50Hz AC. Connect this power supply (with a push button) to an old telephone and it rings the bell on command, but unrealistically fast. I need to take this 60V output and reduce the AC frequency…
Mike Brew
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Number of voice channels for PSTN call

Does Public Switched Telephone Network (PSTN) use two voice channels for a single voice call - one for each direction?
Quirik
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How does this old telephone ringer work?

I bought an old rotary phone with the hopes of cannibalizing it for a doorbell/intercom thing in my apartment building. It looks absolutely marvelous inside: However, I'm having trouble figuring out how the ringer circuit works without taking it…
colinmarc
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Hybrid phone echo cancellation circuit

I'm using a single board computer to talk on a phone line through two coils, one for the TX part, the other for the RX. The phone line is on another coil and then it's connected to a two-wire circuit that leads to an handset. As you know, the…
Metiu
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Hold button for UK Landline telephone

We have retro rotary telephones, and I'd like to make a hold button for the one in my office in the UK. This is literally a "ye olde rotary phone" (1940s) made from bakelite I have fairly basic electronics skills but I don't actually know how the…
CompanyDroneFromSector7G
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What is this part in a “retro” phone?

I’ve got a recently manufactured “retro” landline phone that I wanted to scavenge some parts from, made in 2012 I think. I’d like to be able to do something with the ringer, which appears a lot simpler and more low power than old rotary phone bell…
Rp Wav
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Are the two wires in a telephone cable swappable?

I am in Switzerland. Our landline is delivered through an unshielded twisted pair cable. Are the wires in the pair swappable ? Or does it have a polarity ? The lines is supposed to provide ADSL without POTS. POTS is now deprecated here and the…
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