User's Manual

2650 Watt VHF High Band Transmitter Chapter 4, Circuit Descriptions
435B, Rev. 0 4-27
extinguishes the Enable Indicator at J10-
8. The Low to Q8 turns it Off which turns
On Q7 causing a Low to be applied to Q5
and Q6 that are Biased Off which turns
Off the Module Status Indicator.
A voltage sample from the Switching
Power Supply is applied to Jack J9 Pin 1
of the Board and is connected through
R86 to the front panel Meter for
monitoring. R86 is adjustable to
calibrate the voltage reading on the front
panel meter.
4.2.9.2 Front Panel Metering
A Forward Power Sample of the output of
the Tray is applied to Jack J4 of the
Board. CR11 along with C16 and L3
detect the Peak Level that is then
buffered by U3C, amplified by U3D and
applied to the Front Panel Meter. R44 is
adjustable to calibrate the % Forward
Power indication on the Front Panel
Meter. A Forward Power Sample also is
sent to the Remote Interface Panel. The
Input Forward Power Sample at J4 is split
and fed to the divider R40 and R39 and
then to the Front Panel through Jack J3
for monitoring.
A Sample of the Reflected Power output
of the Tray is applied to Jack J5 and is
detected in the same manner as the
Forward Power. R53 calibrates the Front
Panel Meter in the % Reflected Power
position.
4.2.9.3 Automatic Gain Control
The board contains the Automatic Gain
Control (AGC) function for the Tray in
which it is mounted. An AGC Reference
level input from the Upconverter Tray is
applied to J6 Pin 2 and is amplified by
U3B. The Output of U3B is split with one
path directed to the Front Panel Gain
potentiometer that sets the Output Power
Level of the Tray. The Voltage at the
arm of the Front Panel Gain Pot is
amplified by U2C and compared to the
Output Power of the Tray by U2D. The
Error Voltage from U2D is sent through
J1, when S1 is in the Auto position, to
the Variable Gain/Phase Board on which
it connects to the Pin Diode Attenuator
circuit. This AGC Voltage Level is
metered on the front panel through J13.
The Tray can also be operated in Manual
Gain by switching S1 to the Manual
Position and adjusting R5 for the desired
Output Power Level.
The other path at the output of U3B,
directs the Input AGC Voltage to the
amplifier U6D whose output is fed to the
(+) Input of the comparator U6C. A
Sample of the Forward Power Level of
the Tray at U3D is amplified by U6A and
fed to the (-) Input of the comparator
U6C. The two levels are compared by
U6C and the result is fed to U6B whose
output is controlled by the reference level
set by R75 and R76. If the Difference
between the Output Power Level and the
Input Level drops significantly, U6B Pin 7
goes Low, Q5 and Q6 Turn Off causing
the Module Status LED to go out and the
Remote Module Status to be removed.
4.2.9.4 Operational Voltages
U7 is a 3 Terminal Regulator IC that
takes the +28 VDC input from the
Switching Power Supply and produces
the +12 VDC needed for the operation of
the Board. U8 is a +5 VDC Regulator
that takes the +12 VDC input from the
Exciter Tray or from the Board and
produces the +5 VDC needed to power
the front panel Indicators. Using the +12
VDC from the Exciter Tray permits the
operation of the Front Panel Indicators
even if the Switching Power Supply is not
Turned On.
4.2.10 (A10) +28 VDC Switching
Power Supply Assembly
(A10) The +28 VDC Switching Power
Supply uses the AC input through the
15A circuit breaker CB1 and provides the
+28 VDC needed for operation of the
tray.