Technical Manual

MX100 Series - 100 Watt UHF AMPLIFIER
TSM 20-308 rev 1: April 3, 2000 9 100 W UHF Amplifier
GENERAL DESCRIPTION
INTRODUCTION
This manual describes the LARCAN 100 watt UHF amplifier which is designed to operate on channels 14
through 69. This solid state 100 W UHF amplifier was designed to operate conservatively at 100W peak
sync visual RF power, and 10W average aural carrier RF power, with superb performance, reliability and
operating economy. This amplifier accepts an on-channel internally diplexed (in a 10:1 ratio vis to aur)
composite driving signal of about 10mW peak visual RF as input to its RF chain.
The 100W amplifier and channel processor chassis’ are designed to fit in a single 19" customer-provided
cabinet rack, and require 15.75" (9RU) of vertical panel space for a complete transmitter or translator
system. Alternatively, a 19" customer-provided tabletop cabinet could be substituted if the site requires it.
The RF amplifier heatsink has its own integral cooling fans, and other sub-assemblies are convection
cooled. The simplicity of design, the deployment of all modular and other subassemblies, and the use of
standard readily available components, also enhances serviceability.
Peak forward and reflected power are displayed on an analog percent power meter located on the front
panel of the amplifier unit.
AMPLIFIER CHAIN
The internally diplexed composite RF output of the channel processor or exciter is fed to a conservatively
designed broadband solid-state Front-End amplifier. This amplifier requires no tuning or adjustment.
Simplicity of operation, reduced maintenance costs and increased reliability are a few of the major benefits
derived from this amplifier.
The amplifier chain consists of four stages of amplification. These are the Front End, IPA1, IPA2 and PA
stages. The first two stages operate in class A and the last two in class AB. The overall gain of the system
is about 42dB.
The Front-End module acts as a pre-amplifier as well as an RF level control of the RF chain. It accepts
control voltages from the AGC and VSWR cutback circuits for maintaining and power cutback purposes
respectively. The 100W transmitter uses a single RF chain, consequently quadrature phasing and
combining are not needed, however, if the need arises the Front End module also has gain and
quadrature phasing controls that can be made available.
The next stage is the IPA1 module. It is based on the MRF181 transistor. This broadband amplifier
delivers about 1W sync peak to the IPA2 module. This amplifier does not require optimizing in the system,
which means that it is not frequency dependent at the RF level it is operating.
The IPA2 and PA modules are functionally identical modules. Physically, the only difference is that the
IPA2 module has input and output SMA connectors, and the PA modules do not. Under RF operation the
bias on both IPA2 and PA modules are adjusted to optimize the overall intermodulation products and
differential gain.
TRANSMITTER CONTROL
Interlocking in the 100W simply consists of a jumper as a default connection. The terminals are marked
INTRLK on 1TB1. Antenna or dummy load interlock can be substituted for this jumper.
All control wiring of the transmitter passes through a control circuit board (prefix 2 of the P/S chassis), and
facilities can be provided on this board for telemetry, status, and control connections to and from a remote
control system.
A thermostat is provided in the PA heatsink to open the interlock chain and shut down the power supply