Plug-in OPX Card

The Plug-in Off Premise Extension (OPX) Card is used to provide high voltage isolation for a wide variety of telephone voice grade applications involving the bi-directional transmission of AC and DC voltage. It is available in three options, as listed below:

  • 7501-16C designed for a -48 Vdc referenced to station ground
Product Number CLEI Number Description Download Documents
7501-16C NPPMP291AA Plug-in OPX Card Specifications Installation Guide


  • Direct Inward Dial (DID) loop start
  • Automatic ring down
  • Radio keying
  • Loop start telephone
  • Call waiting pulse
  • Forward disconnect
  • Caller ID
  • Coin telephone (two cards required)
  • Simplex continuity when used with four-wire DX signalling
  • Fax and dial-up “smart” modems (up to 56.6 Kb modem, speed of 45.3 Kb/s if line permits)


  • The card may be used with both the old and the new generation 3-, 5- and 8-card Teleline Shelf
  • The OPX Card is completely bi-directional to all loop signalling, i.e. line voltages can originate from either Station or CO side loops. Bi-directional modulator/demodulators are used to realize a circuit which behaves as an ideal 1:1 isolation device
  • Varistors provide transient voltage protection to the isolation device
  • The OPX Card provides low loss, full duplex DC to voice band communication
  • The OPX Card transmits on/off-hook, dial pulses or touch tone signalling, ringing, polarity reversals, AC and DC voltage and current levels
  • Impedances applied to either side of the card are reflected to the opposite side

The card can be housed in the 3-card shelf, the 5-card shelf, the 8-card shelf, or in any of our High Voltage Interface (HVI) pre-configured units.