User Manual

DRAFT RF Front End System Integration Manual
044-05082 Rev. A
4-1
March 2001
Section 4 Principles of Operations
4-1 Introduction
This section contains a functional description of the Powerwave RFFE MCPA System. Refer to
figure 4-1 and figure 4-3 for the system and amplifier functional block diagrams respectively.
4-2 RF INPUT Signal
The maximum input power for all carrier frequencies should not exceed the limits specified in sec-
tion 1, table 1-1 of this manual. For proper amplifier loop balance, the out of band components of
the input signals should not exceed -60 dBc. The input VSWR should be 2:1 maximum (or bet-
ter).
4-3 RF OUTPUT Load
The load impedance should be as good as possible (1.5:1 or better) in the working band for good
power transfer to the load. If the amplifier is operated into a filter, it will maintain its distortion
characteristics outside the signal band even if the VSWR is infinite, provided the reflected power
does not exceed one Watt. A parasitic signal of less than one Watt incident on the output will not
cause distortion at a higher level than the normal forward distortion (i.e. -60 dBc).
4-4 System Functional Description
A two unit configuration, the RFFE is comprised of a weatherproof (NEMA 4 rating) outdoor Mast-
head Unit (MHU) booster system and an indoor rack mount Masthead Unit Interface (MHUI). The
MCPA system operates in the PCS frequency range of: 1850MHz to 1910MHz (receive) and
1930MHz to 1945MHz (transmit).
4-4.1 The MHU
The MHU has two solid-state power amplifiers for the transmit signals and low noise amplifiers for
the receive function. Both transmit and receive systems are redundancy protected, and in addi-
tion, there is space diversity provided for the receive system (see figure 1-1). The MHU employs
a common box unit that interfaces the two transmit modules to the MHUI. Signals to and from the
MHU interconnect to the base station transceivers through the indoor MHUI control.
4-4.2 The MHUI
The MHUI is the interface between the MHU system and the host base station. The MHUI reports
alarms via the RS-485 bus or form-C interface (see figures 2-3, 2-4, 4-4 and tables 2-3 and
2-6) and displays alarms using an LED display (see figure 1-1 and 3-1). The MHUI houses a low
power duplexer, control board, the system control panel, a preamp, and the cell size variable at-
tenuators (both transmit and receive).
The composite RF signals from the base station radios are applied to the J1a (TX/RX TO MHU)
connector at the rear of the MHUI. From there the signal passes through a combiner a voltage
variable attenuator (VVA) for cell size setting, a second attenuator for cable loss normalization a
diplexer, a third VVA for cable loss normalization, then out through a two-way splitter. Each leg of
the splitter passes through an isolator, then the blind-mate connector to interface with the MCPA.
The signal returns to the MHUI via the blind-mate connector after being amplified by the MCPA
modules. The active power combiner combines the two high-power signals. The active power
combiner has the capability of switching MCPA channels off-line by the use of RF switches. If an
MCPA is not present, turned off, or faulted, the switch will open in that channel and physically dis-
connect that MCPA. The combiner maintains its low insertion characteristics when used in the