User's Manual

350-Watt Digital VHF LB Transmitter Chapter 2, System Description, Maintenance &
Remote Control Connections
DT325B, Rev. 0 2-3
pin diode circuit is connected to the
output of the Upconverter Module,
approximately +10 dBm in level, at J23,
on the rear panel of the Driver/Amplifier
Chassis Assembly. This output is cabled
to the (A10) splitter and then the VHF
amplifier tray in the system.
2.2.3: Adaptive Equalization Circuits
The adaptive equalization circuits for the
system are contained in the Axciter
Modulator which controls the K2 relay
whose output connects to the
downconverter module mounted in the
Driver/Amplifier Chassis Assembly.
Two transmitter output samples are taken
from directional couplers located before,
pre-filter, and after the channel mask
filter, post-filter, that are applied to the
external K2 Relay. The switching of the
relay between the pre and post filter
samples is controlled by the Axciter
Modulator through J7 on the rear panel of
the tray.
The pre or post filter sample is connected
to J12 the Downconverter RF input jack
located on the on the rear panel of the
Driver/Amplifier Chassis Assembly. The
downconverted IF transmitter sample
output of the downconverter module at
J13, on the rear panel of the
Driver/Amplifier Chassis Assembly, is
cabled to J2 on the Axciter Modulator.
The signal is digitized by the Axciter
modulator and demodulated in non-real
time software. The result is analyzed to
calculate linear and nonlinear adaptive
equalizers to improve the transmitted
signal quality by compensating for the
nonlinear compression of the power
amplifier, and the linear distortions
(mostly group delay effects) of the channel
filter.
When a linear adaptive equalizer is being
calculated, the transmitter sample is taken
after the channel mask filter so that its
linear distortions can be “seen.”
When a nonlinear adaptive equalizer is
being calculated, the transmitter sample is
taken before the channel mask filter, so
that the distortion sidebands being
generated by the power amplifier can be
seen (the channel filter would remove the
out-of-band sidebands).
The Axciter modulator contains a standard
Personal Computer. The PC performs user
interface functions and the numerical
processing necessary for the adaptive
linear and nonlinear equalization. The PC
is not in the forward signal path; if it fails
the exciter will continue to generate a
signal with the most recently calculated
equalization.
2.3: VHF Low Band Amplifier Tray
(1304363; Appendix D)
The tray provides approximately 54 dB of
gain. The tray contains (A1-A1) the phase
shifter board 1198-1602 and (A1-A2) the
Filter/amplifier board 1198-1606, which
are mounted in the (A1) RF enclosure
assembly. The (A2-A1) VHF low band
amplifier board 1198-1605, the (A2-A2)
Overdrive protection board 1198-1601 and
the (A2-A3) 3-way splitter board 1198-
1608, which are mounted in the (A2) RF
enclosure assembly. The (A3-A1, A3-A2
and A3-A3) low band VHF amplifier pallets,
P400-VHF-L-18, 1304348 which are
mounted in the (A3) RF enclosure
assembly. The (A4-A1) 3-way combiner
board 1198-1626 and the (A4-A2 & A4-
A3) Low pass filter boards 1198-1628,
which are mounted in the (A4) 3 way
combiner enclosure. The tray also
contains the (A5) AGC control board
1306482, the (A8) Current metering board
1304362 and (A10) the +30 VDC
switching power supply assembly
PM3329B-5-1-R-2-E, 1301504.
The On Channel RF signal (0 to +10 dBm),
enters the rear of the Tray at the "BNC"
Jack J1. The RF connects to a phase
shifter board that provides a phase shift
adjustment of the RF Signal that is needed
to produce the maximum output during
the combining of multiple Amplifier Trays
in an Amplifier Array. The output of the
phase shifter is cabled to the
filter/amplifier board. The gain of the tray