Selective Calling Telephone (Group Phone)
This is a desk type telephone employing DTMF signaling and reception to provide 2 Wire / 4 Wire (separate versions) communication and selective calling on any type of OMNI bus Communication Channel without any auxiliary equipment.

This consists of a DTMF generator, line interface, speech circuit housed in an aesthetic telephone cabinet. It works on 12 V DC supply. Battery backup and built in float charger can be provided (Optional). This system is meant for operation on overhead lines, underground cables, and Microwave or Fiber Optic links.


It employs standard CCITT Dual Tone Multi-frequency code for signaling the distant stations. The desired station is called by pressing a key on a 4x3 matrix key board corresponding to its assigned code. Each station can be assigned a station code by strapping a lead. It is possible to assign a maximum of 12 station codes. A Led (Yellow) is provided to indicate code transmission. A piezo buzzer will ring for 4 seconds and a Red LED will flash whenever a station is called. Ring back tone is available to the calling party to confirm correct reception of a transmitted code. Communication with called station is established through the Handset provided.

General Specifications:
Tummala Product Code: TEL/SCT/01
RDSO IRS Number: TC 80/2000
Operating voltage: 12-18 Volts DC. 6 Volts models also available.
Current consumption: < 15 mA

Code Generator:
Number of Station Codes: 12 (11 + 1 All Call)
Signalling Frequencies: 697, 770, 852, 941, 1209, 1336, 1477, 1633 Hz
Signalling Level: -5 dB

DTMF Decoder:
Code setting: By a shorting link provided inside the telephone
Minimum detectable level: < -20 dB
Ringing: Piezo Buzzer
Ring duration: 4 Seconds
Ring back tone: -10 dB

Speech Characteristics:
Send Level: > 0 dB
Receive Level: > -2 dB
Side tone: < -20 dB (for 2 Wire)
Insertion Loss: < 1.5 dB