Phone system notes

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Mobile style

See Electronics notes/Cell phone notes

Landline style

POTS usually refers to Plain Old Telephone Service - often meaning in context of phones or acoustic modems, and in the last case often in contrast with broadband internet.

PSTN (Public switched telephone network) carries a similar meaning.

Dutch POTS Voltage and protocol:

  • a line that is not ringing has about 48V DC on it
    • Apparently standardized to be between 44 and 56
    • Apparently 32V in an internal home phone system
  • ringing is an alternation netween that voltage and 0V, at 10HZ (or 20Hz? or 25Hz?).
    • (Slow digital multimeters may pick this up better on the AC setting)
  • A line in use has ~5V or/to ~10V DC with tones/voice on top of it


  • There is the concept of Ringer Equivalence Number, which is an indication of load in somewhat arbitrary units, though may be locally standardized. Phones usually take 1, sometimes more.

(verify) all of this.

Connecting phones or modems together



Devices on a line

Notes on basic service, phone line switching, and dialing

Much more interesting watching