User Manual

ADCP-75-179 • Preliminary Issue A • September 2004 • Section 1: Overview

Page 1-7

3 SYSTEM FUNCTIONS AND FEATURES

This section describes various system level functions and features of the Digivance system.

3.1 Fiber Optic Transport

In a typical Digivance system, the HU is connected to the RU over two single-mode optical

fibers. One fiber is used to transport the forward path optical signal. The other fiber is used to

transport the reverse path optical signal. Because the optical signal is digital, the input and

output RF signal levels at the HU or the RU are not dependent on the level of the optical signal

or the length of the optical fiber. A diagram of the fiber optic transport system for a typical

Digivance system is shown in Figure 1-7.

Figure 1-7. Standard Fiber Optic Transport Application

The maximum length of the optical links is dependent on the loss specifications of the optical

fiber and the losses imposed by the various connectors and splices. The system provides an

optical budget of 25 dB (typical) when used with 9/125 single-mode fiber.

In some applications, it may be desirable or necessary to combine the forward path and reverse

path optical signals from a single HU/RU pair onto a single optical fiber. This can be

accomplished by using a passive bi-directional Wavelength Division Multiplexer (WDM)

system. The optical wavelengths used in the Digivance system are 1550 nm for the forward path

and 1310 nm for the reverse path. Because different wavelengths are used for the forward and

reverse paths, both signals can be combined on a single optical fiber. One WDM module is

mounted with the HU and the other WDM module is mounted with the RU as shown in

Figure 1-8. The WDM system is available as an accessory item.

Figure 1-8. Wavelength Division Multiplexer Application

HOST UNIT

18526-A

REMOTE

UNIT

FORWARD PATH

REVERSE PATH

FIBER OPTIC

LINK