b. Replace all rear panels and apply single phase and three
phase AC power to the transmitter. The Low Voltage circuit
breakers CB1 and CB2 should be ON and the PA OFF
switch S2 on the Controller should be OFF (up).
c. Depress the LOW power button. The +230 VDC PA Power
Supply should come up as in the RF drive checkout.
Compare all meter readings with Factory Test Data.
d. Turn the PA OFF switch S2 on the Controller to the ON
(down) position.
e. Change the front panel Multimeter switch from the PA
+VDC to the DETECTOR NULL (ANTENNA) position.
The power meter selector switch should be in FWD.
f. Raise the output power by depressing the RAISE button.
Observe the following while raising the power:
1. Power and Current should increase.
2. DETECTOR NULL (ANTENNA) indication may be-
gin to rise depending upon the degree of mismatch
between the station load and the factory test load,
especially if the transmitter is loading into the antenna.
This may cause ANT VSWR trips and prevent full
power operation until this circuit is adjusted.
3. If ANT VSWR trips occur, the Antenna VSWR Phase
Angle Detector on the Output Monitor will have to be
adjusted. The Bandpass Filter VSWR Phase Angle De-
tector may also require adjusting, but should be done
after the TUNE and LOAD controls are adjusted for the
proper PA voltage/current ratio.
In brief, adjust C15 and L12 on the Output Monitor for minimum
reading on the multimeter DETECTOR NULL (ANTENNA)
position. Adjust C16 and any of the coils (L5, L6, L7, or L8)
switched in by S7 on the Output Monitor for a minimum reading
on the DETECTOR NULL (FILTER) position. Refer to SEC-
TION V, Maintenance, for the Output Monitor adjustment pro-
cedures.
2.15.7.1
Tuning for Voltage/Current Ratio
a. At 25 kW power output, the PA Supply Current should be
between 105A and 123A depending on the AC line voltage.
Refer to the Factory Test Data and use the following
information to help tune the transmitter for the correct PA
Supply Voltage/Current ratio.
1. Power Output (meter)
2. PA Voltage
3. PA Current
4. PA Efficiency
5. # of Steps turned on
b. The RAISE control determines the number of steps (PA
Modules) turned on. When a PA Module is ON, the green
LED on the module is illuminated. With a PA Power
Supply voltage of +230 VDC, there should be 23 PA
Modules on for 25 kW output.
c. The LOADING control adjusts the PA Supply Current and
power output. With a PA Power Supply voltage of +230
VDC, PA Supply Current should be between 110 and 115
Amps.
d. The TUNE control is adjusted for a PEAK in power output.
This control is rather broad, especially at the low end of
the medium wave band.
2.15.8
Setting Modulation Monitor Sample Levels
An adjustable 1 to 10 Volt RMS signal is available at the Output
Monitor. The RF sample is set for the proper level at the LOW-
EST operating power by adjusting 2L7 in the Output Network
Compartment. When the LOW Power sample level has been set,
MEDIUM and HIGH power levels are adjusted by R7 and R8 on
the Output Monitor.
a. Set the LOW power output of the transmitter to the lowest
power that will be required for normal operation.
b. Measure the RF voltage level at the monitor. If the level
must be increased or decreased to meet modulation moni-
tor input voltage requirements, the tap on 2L7 must be
adjusted.
WARNING
TURN OFF ALL SINGLE PHASE AND THREE PHASE PRIMARY
POWER AT THE MAIN DISCONNECT BEFORE REMOVING ANY
REAR PANEL.
c. Remove the rear right panel from the Output Network
Compartment.
d. Locate Modulation Monitor sample coil 2L7 connected to
the RF output flange. To DECREASE the sample voltage,
move the tap closer to the grounded end of the coil. To
INCREASE the sample voltage, move the tap away from
the grounded end of the coil. Move the tap 1/4 turn in the
desired direction. Be careful not to short adjacent turns
when positioning the clip.
e. Replace the Output Network Compartment rear panel.
Reapply single phase and three phase AC primary power
at the disconnect switch. Depress the LOW power switch.
f. Measure the RF sample voltage. Repeat the coil adjust-
ment procedure until the desired sample voltage for the
LOW power setting is obtained.
When the LOW power sample level is satisfactory, continue with
the following steps:
g. Turn R7, MEDIUM power modulation monitor sample
adjustment, on the Output Monitor fully CCW (counter-
clockwise).
h. Turn the transmitter on at MEDIUM power, or, if the
transmitter is already on at another power level, depress
the MEDIUM power switch. Use the RAISE and LOWER
buttons to set the MEDIUM power output.
i. Adjust R7 on Output Monitor until the sample voltage at
the modulation monitor is the SAME as it was in the LOW
power position. This adjustment can be made while the
transmitter is operating.
DX-25U
2-10
888-2297-002
Rev. AA: 8/9/2000
WARNING: Disconnect primary power prior to servicing.
