Why do phone lines need power?

Question

I don't understand why phone lines need power or even why you need a dial tone. If anyone could clear up this whole issue for me that would be great. I'm trying to design a system where two modems interact with eachother but i apparently need a dial tone in order for it to work. So i'm wondering if i can find out why the modem or phone needs it, i can find an adequate work around.

Thank you in advance.

Answer 1

you need a power  to operate the system because it works basically like a switch

phone systems were designed  not to need any external power to work

so they use the supplied power from  the phone line

Answer 2

so it can ring?, and so you can talk to and hear the other person?

Answer 3

Phone lines don't need power...modems do. PHONE COMPANIES need power (used at the phone companies main base) to send and recieve electronic signals from phones. They send these signals through their own privately owned "phone lines"(not electric lines). Recently most modems plug in to the wall through a regular 120 volt port(electric company) and send and recieve electronic signals from cable lines HDMI or "cable ready" (Comcast,  DSL...etc). These recievers (modems) need power and /or a fiberoptic connection to a main connection company.  

If you have a high speed modem...it needs a high speed connection (not a phone line). If it is dial up, then you need a phone line or a dial tone.

Answer 4

dial tone is not a requirement of phone service, and in the beginning there was no dial tone.. dial tone was designed so that when you pick up the phone you know that your line is working, and you are able to place a call...

depending on if your modem is looking for dial tone or just the proper voltage on the line...

on hook voltage is 48-52VDC

off hook voltage is around 8-12VDC

ringing voltage is around 110VAC (but VERY LITTLE amprage, dont plug it into house current)

Answer 5

Rather than me try and give a long-winded explanation here,

the following document gives a complete overview of how telephone circuits work and why:

Answer 6

joe is mostly correct except modems dont look for voltage, i assume you are talking a dsl modem, it is possible to run naked dsl which is simply dsl without the dial tone on the same line, the dsl doesnt send any voltage down the line.

Answer 7

Also, side note.

Phone lines draw their power from the line itself, and it needs power to make the phone ring.

Some phones do not require an electrical outlet for this reason.