Western Electric 202T

Bell System EDI-to-DTMF Audio Transcoder

CD (CARRIER)
TX DATA
DTMF LOCK

1. EDI X12 / Raw Payload Buffer

BAUD / TONE SPEED 85 ms/sym
STATUS: IDLE // LINE READY (350Hz+440Hz)
CHAR: - ASCII: -- FREQS: --- / --- Hz
Live EDI Character & DTMF Frame Stream (Click any character to audition) 0 symbols

2. CRT Acoustic Oscilloscope & FFT

697–1633 Hz DTMF MATRIX
CH1: TIME DOMAIN WAVEFORM NO CARRIER
CH2: HARMONIC SPECTRUM BELL 4x4 AUTOVON / X12

3. Bell 16-Key Touch-Tone Matrix

Lights up during EDI playback or press keys manually

ITU-T Q.23
ROW \ COL
1209 Hz
1336 Hz
1477 Hz
1633 Hz
697 Hz
770 Hz
852 Hz
941 Hz
HOW EDI MAPS TO BELL AUDIO:
• Direct Keypad Mode: Numbers 0-9 play native DTMF; * plays Star (941+1209Hz); Segment terminator ~ plays # (941+1477Hz); Letters map to Bell phone keys + priority carrier.
• 16-Key Hex DTMF Mode: Encodes every ASCII byte into two lossless Bell 4x4 nibbles (0-9, A-D, *=E, #=F).