User's Guide

Theory of Operation

The 48900 signal boosters are designed to enhance radio communication in buildings, basements,

tunnels and other RF shielded environments. The 48910 is tuned for the 800 MHz Cellular band, the

48920 for the 800 SMR band and the 48930 for the 900 MHz SMR band.

These units work by receiving and amplifying the base TX signals via a donor antenna directed at the

desired base site. This RF path is called the downlink. The amplified base TX signal is re-radiated via

antenna(s) or radiating cable into the Service Area. Subscriber mobile RF signals are received by the

same service area radiating elements and amplified in the uplink RF path to be radiated back to the

base via the donor antenna.

The LNAs and Power Amplifiers are broadband. The same amplifiers are used for the uplink and

downlin. Likewise, the control board is the same for both models. Differentiation is provided by the

duplexing filters on the base and service area connectors that determine the basic passband and

direct the RF signals to the proper gain path, uplink and downlink respectively.

Both the downlink and uplink have Automatic Gain Control (AGC) in the power amplifiers to prevent

an overdrive condition. Manual gain adjustment is provided in the LNA stage. Overdrive limiting is

provided by the AGC circuitry and set at the factory. This ensures that the unit will not exceed FCC

limits for spurious emissions.

The control board distributes DC power to the amplifier modules and monitors each module for any

fault conditions. LED indicators provide visual diagnostics and a NC / NO relay provides for remote

notification for any fault condition.

Block Diagram