Axcera DT325B, Инструкция по эксплуатации

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350-Watt Digital VHF LB Transmitter Chapter 4, Circuit Descriptions
DT325B, Rev. 0 4-10
transmitter is switched to Operate. The
Enable is applied to (A5) the AGC Control
Board (1306482), which, if there is no
Thermal Fault, connects the Enable from
J10 Pins 6 & 7 to J1-18 & 14 on the
Switching Power Supply Assembly. The
Green Enable Front Panel LED (DS2) will
light, indicating an Enable is present. If
the Amplifier Array is in Standby or if a
Thermal Fault occurs, the AGC Control
Board will not Enable the Switching
Power Supply, therefore the +28 VDC will
be removed from the Amplifier Modules
and the Front Panel Enable LED and
Module Status LEDs will be out.
The front panel Meter (A9), by switching
(S1) the Front Panel Selector Switch,
monitors the AGC Voltage, % Output
Reflected Power, % Forward Power and
the Switching Power Supply Voltage (+28
VDC). The Meter in the AGC position will
typically read anywhere from 1 to 2
Volts. The Meter is calibrated in the
Power Supply position using R86, the %
Output Power is calibrated using R44 and
the % Reflected Power is calibrated using
R53, all of the pots located on the AGC
Control Board. With S1 in the Current
Position, S2 is switched to read the
operating currents or the Idling currents,
no RF Drive applied, of the High Band
Output Amplifier Boards. The idling
currents are monitored for the set up of
the devices. Refer to the final Test Data
Sheet for your Transmitter for the
operational and Idling current readings.
The Reflected Power Sample, from the 3
Way Combiner Board, is fed back to the
AGC Control Board at J5. On the board
the Reflected Sample is connected thru
the detector circuit to a VSWR Cutback
circuit (U13C). If the Reflected power
increases above 20%, the output power
of the Tray, as set by R60 (VSWR
Cutback) on the AGC Control Board, is
cutback to maintain a 20 % Reflected
Output level. The Red LED (DS4) VSWR
Cutback, located on the front panel,
remains lit until the Reflected level drops
below 20%.
There are three Thermal Switches
mounted in the Tray for
overtemperature protection. Two of the
Thermal Switches (A13 & A14) are
mounted on (A3) the heatsink for the
Low Band Amplifier Pallets and the third
Thermal Switch (A15) is mounted on the
heatsink for the 3 Way Combiner Board.
The Thermal Switches close when the
heatsink on which it is mounted reaches
a temperature of 175° F. The closed
Thermal Switch causes the AGC Control
Board, to remove the Enable to the
Switching Power Supply, eliminating the
+28 VDC, and also to light the Red LED
Indicator, Overtemperature (DS5),
mounted on the front panel. The AGC
Control Board also extinguishes the
Module Status LED (DS3).
4.3 External Boards
4.3.1 (A4) Triple Peak Detector Board
(1159713; Appendix A)
The Triple Peak Detector Board is
mounted on the Bottom, Right Side of
the Cabinet accessed through the back.
The function of the triple peak detector
board is to detect three power samples
and generate output voltages that are
proportional to the power levels of the
sampled signals for use by the control
monitoring assembly in the transmitter.
There are three signal paths on the
board: one for RF I/P 1, one for RF I/P 2
and one for RF I/P3. The circuits function
as described in the following paragraphs.
The RF sample input enters the board at
the RF I/P 1 SMA jack J1. Resistors R9,
R4 and R10 form a 3dB pad. The RF
sample is amplified by U3 and connected
to a detector circuit made up of R11, R3,
CR1, R8, C7, R41, and C6. For digital
operation the jumpers, W1 on J4 and W4
on J8, are both between pins 1 & 2. The
detected output is buffered by the
operational amplifier U1D and then
connected to RF I/P 1 power adjust pot
R14, which adjusts the gain of U2D. The