View Single Post
Old 18th May 2019, 11:11 am   #5
Station X
Station X's Avatar
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 16,376
Default Re: GPO/BT Call Progress Tones?

Originally Posted by Herald1360 View Post
I believe the "uneven" sounding engaged tone is "equipment busy" rather than "called party engaged".
This was always known as Equipment Engaged Tone or EET.

With the advent of push button "dialing" dial tone was renamed proceed tone, but the name never caught on.

Dial tone was changed from 50Hz square wave to 400Hz sine wave because MF4 dialing didn't work well in the face of 50Hz harmonics which were present until the first keyed digit was accepted.
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now