Extend an Analog DID Trunk Line Over Fiber

Fiber Optic Isolation Systems - 2 Wire DID

The 2 Wire DID (Direct Inward Dialing) fiber link card system provides a fiber optic transmission of a Telco DID TRUNK line to a PBX (loop start) over two optical fibers.

The signal provided over copper wiring is converted to optical, transmitted over fiber optic cable, and converted back into the original copper-based signal at the other end. This allows for network extension over long distances, and provides electrical isolation between both ends.

The 2-wire DID system transmits signals in the voice-frequency or audio range (300Hz-3.4KHz) while providing reverse battery signaling to communicate call status. The 2 Wire DID system is temperature hardened for tough environmental conditions where 24/7/365 operation and rugged reliability are critical, and is covered by our Limited Lifetime Warranty.

This fiber link card is designed to be installed into any of the RLH Fiber Link Card Housings, and occupies a single card slot.


  • Compatible with 2 wire DID Systems
  • DID Sub (PBX) side is line powered
  • DID CO (trunk) uses 24-56VDC power
  • Uses reverse battery switching
  • Available in Single and Multimode
  • Available with ST or SC Connectors
  • Uses 24~48VDC Local Power
  • Compatible with a wide variety of Card Housings
  • Limited Lifetime Warranty
  • Made in USA

Transmission Method:
Frequency modulated light via two optical fibers

Multimode: 850nm
Singlemode: 1310/1550nm

Fiber Type/Distance:
Multimode (62.5/125µm): 1.5 miles/2.4km
Singlemode (9/125µm): 9 miles/15km; Long Haul 37 miles/60km

Fiber Connector Type:
ST or SC

7in. x 4in. x 1in. (177.8mm x 101.6mm x 25.4mm)
(Standard RLH Fiber Link Card Form Factor)

Operating Temperature:
-40˚F to +158˚F (-40˚C to +70˚C)

Operating Humidity:
95% non-condensing

2 Wire DID System
2 Wire DID System

For product questions, volume pricing and/or delivery outside of the US and Canada, please contact sales.


Please contact us to get a quote for your project.

*Lead times are estimates and may vary. You will be contacted within 1 business day to go over the details of your order. If you require a specific date, let us know!
*Days = Business Days

WarningWarning: This product can expose you to chemicals including arsenic, which is known to the State of California to cause cancer. For more information, go to www.P65Warnings.ca.gov.

RLH Industries - Fiber Optic Link
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