User's Manual Part 1

CL1TC-4 400W DVB-H Transmitter Product Description
Product Manual, Rev. 1 18
2.3.5 High Power Amplifier (HPA)
The module provides R
F signal amplification up to the required 400 Watts output
power level at the HPA RF output.
The output power level is maintained via an ALC loop.
The output forward and reverse power levels are measured by the integrated output
coupler and reported to the system controller.
The main system diagram for the High Power Amplifier (HPA) is shown in Figure 2-8
. This
compact design employs a high efficiency LDMOS technology with a 400 Watt power rating. The
HPA includes a LCD display for status messages. The HPA also includes two power supplies and
has two variable speed DC fans for forced air cooling.
The HPA is designed to operate as a final amplification stage for the terrestrial L-Band
transmitter system. It amplifies the L-Band terrestrial signal from the modulator up to a
power level of 400 Watts, while maintaining acceptable output emission levels.
The HPA is a field-replaceable system component that includes integrated AC/DC power
supplies. The HPA is designed for installation in an indoor or environmentally protected
outdoor cabinet.
The HPA architecture is based on a solid state design operating in the Class A/AB linear
mode over a frequency range from 1670 MHz to 1675MHz. The amplifier is fully protected
against input overdrive, overheating and output load VSWR conditions. The protection
circuits are all self-correcting, allowing restoration of the amplifier to the normal operational
state upon removal of the fault condition.
The HPA incorporates an internal automatic self-leveling loop to maintain a constant output
power level. The automatic level control (ALC) circuit will compensate for the input signal
level variations and gain variations affected by changes in temperature as well as for the
gain change due to devices aging.
The HPA main driver chain signal is split and feeds six individual LDMOS power modules. The
output of each module is combined and fed into the combiner/coupler which includes a RF
monitor port and RF detectors to measure forward and reflected power levels. The HPA
controller monitors the operation parameters of the HPA, provides protection against abnormal
operation conditions and communicates with the modulator system controller via a RS-485 serial
link.
There are six output power modules in parallel configuration in the 400W DVB-H HPA. The rated
output power level of the HPA during normal operation is 56 dBm (400W). In the event of a
partial failure (the lowest current reading on one of the power modules is less than 20% of
the highest current reading on one of the power modules), the HPA is capable of operating
with a maximum output power level of 53 dBm. If the output power level is greater than 53
dBm, it will be automatically reduced to 53 dBm. If the output power level is less than 53
dBm, no reduction will occur.