Digital Technology Vs Analog Technology
2011
TELEPHONE Technology question?
What type of power and signal-transmission is more common in “an older land-line telephone system” with old and outdated copper wires?
%I am trying to determine how the signals are sent through the telephone lines in my alley.
I do know and have experience operating a CABLE TELEVISION system; where the signals came from a master antenna via my head-end, to the distribution cables throughout my neighborhood.
Is the Land-line Telephone system the same (operating from a “head-end” and distributing throughout the cables)? or, because this is a TWO-WAY system, how is this different?
(I am not comparing ANALOG vs. DIGITAL signals – I am merely researching how these signals are powered through my alley.)
Thanks for technical help.
P.S. I have my degree in Commercial Electronics, so I know the difference between SIGNAL and VOLTAGE.
The basic analog signal is your voice which is transmitted over what is called a tip and ring line. Standing idle the tip and ring (pair) measures -48 volts DC (and yes that is negative 48 volts DC), when you take the receiver off hook it causes a direct short on the line reducing the voltage to -24 volts DC on each wire.
When you depress or dial a number it sends out another signal called dual tone multi frequency (DTMF), this signal received by the local phone company exchange office located in your area and will decipher the DTMT digits, sending it to the number attempting to be called.
If the calling attempt is successful an inverting process takes place at the Central Office sending a AC (that’s Alternating Current for you people with degrees) burst to the receiving phone. This burst is alternating (on and off) at approximately 90 -105 volts AC (yes it’s really an AC electrical event with very low amperes).
When the party being called picks up the receiver the AC is dropped and replaced with – 24 volts DC (the circuit is complete between caller and the answerer). The -24 volts DC is considered talk battery as Bell Labs discovered many decades ago that negative battery was a much cleaner talk battery as oppose to standard (or what you would consider standard battery) DC battery.
The battery provided to your home phone comes from you local exchange whether it be transformed or standard batteries (true story). Although I have never asked I think it would be safe to say the AC burst is originally provided by you local power company and stepped down at the Central Office.
You will have to ask for details on the digital phone, but you should already have a grasp on that being you are experienced in CATV.
