User manual

ADCP-75-154 • Issue 3 • August 2006

Page 3

• The MHU—located on top of the tower, performs the amplifier function on the uplink

signal. Two subcomponents of the MHU, an RF filter and a Low Noise Amplifier (LNA),

are involved in the amplifier function. The downlink signal is not amplified.

• The PDU—located in the base station, provides DC current for use in the amplifier

function. The PDU outputs the DC current through a front port from which it travels by

way of a short linkage cable to the Bias-T. The injection of the DC current onto the coaxial

cable will not cause interference with signal transmission.

The PDU also monitors the status of all MHUs simultaneously by sensing their current

draws. If any of the MHUs fails, or if there is a cut or short circuit in the coaxial cable, the

PDU gives an alarm to the BTS. The PDU thus also monitors the condition of the coaxial

cable, not just the MHU. The PDU also has built-in lightning protection.

• The Bias-T—located on the coaxial cable, is a passive device that physically injects the

DC current onto the coaxial cable. The Bias-T injects the current into the center pin of the

coaxial cable.

A single PDU supports multiple MHUs (with one Bias-T required for each MHU). The number

of filters/LNAs supported depends on the system type.

1.3 MHU Dimensions

MHU dimensions are shown in Figure 3, Figure 4, and Figure 5.

Figure 3. 900 Narrow Band MHU Dimensions

ClearGain

18790-A

63 MILLIMETERS

280 MILLIMETERS

250 MILLIMETERS

900 Dual Duplex 2-Port TMA