User Manual

INTRODUCTION
This manual describes the LARCAN 30 watt VHF amplifier designed for NTSC
channels 2 through 13. Models 40D2232G1 is for channels 7 through 13, 40D2232G2
for channels 2, 3, and 4, and model 40D2232G3 is for channels 5 and 6. These
amplifiers are used in the LARCAN-USA MX30V series transmitters and translators.
LARCAN all-solid-state 30 W VHF amplifier were designed to operate conservatively
at 30 W peak sync visual RF power and 3 W average aural single 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 1mW peak visual RF, as input to its RF chain.
The 30 W amplifier and channel processor chassis' are designed to fit in a
single 19" customer-provided cabinet rack, and require 7" (4RU) 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 fan, 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 unit.
AMPLIFIER CHAIN
The internally diplexed composite RF output of the channel processor is fed to a
conservatively designed broadband solid-state 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 two stages of amplification for low band and
three stages for high band.
For amplifiers having somewhat more gain than usual, and especially for 10 watt
output applications, the exciter driving the preamplifier may be padded down with
an inline attenuator to avoid overdrive to the preamplifier, because exciters
generally perform better at higher output levels.
The preamplifier uses high gain, broadband, integrated circuit amplifier(s)
operating class A. This preamplifier has two stages in high band models, while a
single stage suffices for low band.
The preamplifier uses the same circuit board that is an integral part of the
"phase quadrature control" that is a required part of paralleled amplifier
configurations. The 30 W transmitter uses a single RF chain, consequently
quadrature phasing is not needed nor used, but some low cost components for it
may remain in place on the board. Removal entails far greater overall expense
than simply leaving them in place.
The PA stage consists of a pair of push-pull FETs in a single case, operating in