Harris DX 25U, Техническое руководство

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Section R
Switch Board/meter Panel (A31)
R.1
Introduction
The switch board provides manual pushbutton control for trans-
mitter ON/OFF functions, allowing LOW, MED, and HIGH
power selection, power raise/lower control, selection controls for
the multimeter and the forward/reflected power readings. LED’s
are provided to indicate the current selections.
The switch board is located on the back of the left Control
Compartment door. The printed wiring board itself is a ‘break-
away’ board, which is split in two pieces which after assembly,
are folded in half, and mounted piggy-back. The half containing
the switches and LEDs is mounted to the panel such that these
components protrude through panel cutouts and are accessible to
the operator. The second half is then mounted on the back of the
first half, and it contains the control circuitry. This is done so that
the height of the components on the second half of the board will
not mechanically interfere with the panel since the board must
be mounted closely to the panel to allow the switches and LED’s
to protrude through.
Refer to the Switch/Meter Board Schematic 839-6208-301 for
the following discussion.
R.1.1
Power Control
See sheet 1. When any of the power control pushbuttons (OFF,
LOW, MED, HIGH, RAISE, or LOWER) are depressed, a
+15vdc command signal is provided to the transmitter power
control section of the Controller. Refer to section P (Controller)
for ON/OFF control logic circuit descriptions.
Indicator LED’s are located above each switch (with the excep-
tion of the OFF switch) which illuminate when their correspond-
ing switch has been depressed. Each LED is connected to the
+15vdc bus through a resistor. The other side of the LED’s are
connected to an open collector output from the Controller.
R.1.2
Multimeter Circuit (M1)
R.1.2.1
Meter Selection Circuit
See sheet 2. The multimeter selection is done by repeatedly
depressing the multimeter selection pushbutton switch until the
desired function is reached, indicated by an illuminated LED
next to the desired function labeled on the front panel.
Each appropriate metered signal is provided to the board via the
ribbon cable connected to the board at J1. Each line is terminated
with the appropriate impedance and with a bypass capacitor.
Each signal is interfaced via a voltage follower op amp (U2, U4,
and U5) and provided to multiplexer U3, which then selects the
appropriate line to be fed to the multimeter corresponding to the
selection made with the front panel switch.
The corresponding LED is illuminated similarly by demulti-
plexer U8, which selects the appropriate LED to illuminate
corresponding to the selection made with the front panel switch.
The LED’s are connected to the +15vdc bus via resistors, then
through driver IC U1, through the demultiplexer, to ground.
Both multiplexer U3 and the demultiplexer U8 are addressed via
a counter IC U6, which is incremented by each closure of the
selection switch. At power up, the address is set to 000, which
selects the first multimeter position automatically.
R.1.2.2
Metering Circuits
The 100ua movement meter used as the multimeter is driven by
a final op amp (U9A) and has an RF bypass cap (C41) and a
filtering cap (C1). The filtering cap helps remove any transients
from the power supply, and removes any ripple from the -15vdc
converter regulator IC, U14.
Each meter signal is provided from the metering circuits de-
scribed following.
a. PA +VDC (+230vdc supply): Multiplier resistors are lo-
cated on Fuse board A24, and buffering is provided on the
Controller board.
b. ANTENNA NULL and FILTER NULL: These are detec-
tor null indications for the VSWR detector circuits on the
Output Monitor. Buffering of these signals is provided by
op amps on the Controller board.
c. RF DRIVE: The Relative RF Drive signal is taken from
RF drive sample circuit located on the LED board. The ‘RF
drive estimate’ output is routed through the Controller to
the switch board.
d. +/- 22vdc, +/-8vdc: These positions indicate unregulated
output voltages from the Low Voltage power supply. The
multiplier resistors for these voltage scales are located on
the Controller.
R.1.3
Supply Current Meter Circuit (M2)
The power supply current sample is taken from a shunt resistor
in the negative output of the 230 volt power supply. The voltage
developed across the meter shunt is proportional to the supply
current (and is 50 millivolts when supply current is 100 amperes).
This voltage is brought to J1-36 and J1-37 on the Switch
Board/Meter Panel printed circuit board, and is routed through
Controller Board A38 to Overcurrent fault and overload circuits
on LED Board A32. See sheet 2.
R.1.4
Power Meter Circuit (M3)
Buffering of the forward and reflected power samples is provided
by two sections of op amp U5. The U5 output signals are routed
through multiplexer U10, op amp U9, then to the power meter.
Selection of forward or reflected power is accomplished by
multiplexer U10, which is driven by flip flop U11. Switch S8
toggles flip flop U11. Display of the selected metering function
is provided by leds DS8 and DS9.
Upon application of dc power, the forward/reflected meter
should be in forward power position, as determined by the Set
input to flip flop U11.
Rev. R: 11-11-96 888-2297-002 R-1
WARNING: Disconnect primary power prior to servicing.