Telephone line signal!!!!!

Hi,
I m new here and didnt know where to post this one and so decided to do it here.
I f wrong please tell me where to post it.
i would like to know exactly what type of signal flows through telephone lines.
For i m sure definately pure voice signals cannot flow thru, telephone wires or there will be so much data loss it will become erraneous.
So help me pls.

Hi.
The ringing signal is around 20Hz, 90VAC
The DC supplied at the central office CO is 50V DC, in series with relay coils of about 400Ω.
The resistance of the line varies with the distance to the CO, up to around 1KΩ
The balanced audio bandwidht is limited from 300Hz to 3KHz. The audio level is transmitted at about -9dBm
The dialing is by generation of dual tone multi frequency DTMF combination of 16 sinusoidal audio tones at a level of 0dBm
The signalling is around 440Hz, the cadence varies, the levels go from -25dBm to -10dBm.
Each country has its own regulations corresponding to the word 'varies' or 'around' above.
Modern central offices have electronic circuits instead of relays, but still manage the signals the same way.
Miguel

Hi,


A lot of info @:

https://www.epanorama.net/links/telephone.html

Externet said:

Hi.
The ringing signal is around 20Hz, 90VAC
The DC supplied at the central office CO is 50V DC, in series with relay coils of about 400Ω.
The resistance of the line varies with the distance to the CO, up to around 1KΩ
The balanced audio bandwidht is limited from 300Hz to 3KHz. The audio level is transmitted at about -9dBm
The dialing is by generation of dual tone multi frequency DTMF combination of 16 sinusoidal audio tones at a level of 0dBm

Click to expand...

hmm... if remember right DTMF give -9 dBm on high tone group and -11 dBm on low tone group and totale power is around -7 dBm over 600 Ohm impedances

practical phone line can give around 900 Ohm//110 nF complex impedances (depend of contrys type of cable design in phone network) and capacitances attenuate high frequencys more than low. '-11 - -9 dBm' shift between tone groups in DTMF designed for compensate this cable characerstic.



Only air hanged lines pair with 1.3 feet (4 dm) distance between conduct can give pure resistive impedances as 600 Ohm for LF-requency and give very low loss and can transporting phone signal 10 - 100 km and more without any gain.

Phone companys try to move air hanged lines to cables (begining for atlantic cables) give very serious problem with high loss and high attenuate on high frecuency in beginning of 1900 - and not understude why, and to days well know names as Nyqvist and Pulpin (coils in series every 300 metres (1000 feet) ) is two of many peoples thinking to solve this problem and builds importent rules and equations still using to days and very importing for whole telecomunications industries...

One of them are 'telegraph equation' do describe transmissions line, and many 'digital people' not want know this and make serious misstake by design like shit as IDE-bus and USB-bus and limit perfoments to short distance and low capacity (1 feet with special high density ribbon cable for high performents IDE-bus, 4 metres of USB, timing problem on backplane and circurit board depend of reflection et cetera) compare to SCSI and Ethernet build of people with know of transmission theory and make acceptable compromisses between perfoments and prices - and leave high distance to roof by design for future capacity improvements - many times.

The signalling is around 440Hz, the cadence varies, the levels go from -25dBm to -10dBm.
Each country has its own regulations corresponding to the word 'varies' or 'around' above.
Modern central offices have electronic circuits instead of relays, but still manage the signals the same way.
Miguel

Click to expand...

voice signal is convered to electrical sinal first .then it is transmitted.at the reciver we again converted it back.

hi
voice signal is converted into electrical signal using transducers.
then this analog signal is quantized and digitized. The digital signal is converted into light in OFC. this is the transmitter part.
the receiver is the reverse of the same, except the quantization(it is irreversible).

phone line has two cables red and green. red one is negative and green one is positive. they are also called tip(green) and ring(red).
the ringing signal can vary between 40-150VAC and average frequency 20 Hz. in europe it is 25Hz.
on the other hand central office gives you a dc signal which is 48V but very low current about 5uA.