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MODEL 2945


General Description: The Telephone Coupler provides an interface to the PSTN (Public Switched Telephone Network) in compliance with the FCC Part 68 Registered Protective Device/DOC CS-03 Certified Network Protective Device to the following units.

Use with: 5493, 5109, 5212S and 2109.

It offers modular packaging design, 2 or 4 wire operation, squelch indicator and off the shelf availability. The unit is designed to perform as a complete voice/data telephone interface with telephone line isolation and transmit level/billing delay squelch.



Transmit Section: When the HOOK lead of the DB9 system interface connector is pulled down to 0 V from the internal power supply the change of state latches the hook-switch allowing loop current Tip/Ring.

A two second delay (minimum) is required after seizing the line prior to sending data in accordance with FCC Part 68 regulation. Once the line is seized the unit provides a typical 2.35 second delay squelch prior to opening the communication path.

Voice/data is then able to be transmitted.

Receive Section: Upon detection of an incoming Ring Signal a 12 V signal is placed upon the RING DETECT lead of the DB9 connector. The users external equipment then pulls the HOOK lead low. The coupler then waits for the billing delay squelch to time out before connecting the communications path.

A LED is provided to indicate squelch which is driven by a comparator within the unit and operates on excess input level.



  • Power Supply: +11 to +32 Vdc; (Off-Hook current 95 to 125 mA, On-Hook 55 to 95 mA).
  • Telephone Line Interface: 600 ohm reference.
  • Surge Protection: Conforms to all FCC surge, hazardous voltage and leakage requirements.
  • Transmit Input Level (MAX.):
  • 2-Wire Mode: 0 to -2 dBm (Ref. 600 ohm) with 10 dB loss to telephone line Interface (-10 dBm/600 ohm output).
  • 4-Wire Mode: 0 to -2 dBm (Ref. 600 ohm) with 9 dB loss to telephone line Inerface.
  • Transmit Overload Squelch: Average time 3 seconds typical. Note: Transmit levels may exceed the maximum levels by 5 dB if the average level within the transmit overload time does not exceed the specified maximum levels.
  • Operating Temperature: 0 C to +70 C. Maximum upper limit decreases with higher input voltages.