k. Operate the transmitter again at 25 kW. If no waveform
appears, then depress the RAISE or LOWER button until
this step turns on.
l. As the power is changed, the Binary amps are turning on
and off at different rates. The vertical sensitivity of the
scope can be increased since B7 through B10 operate at
1/2 the supply voltage.
m. If the Phasing of B7 is /-5 degrees, move to B9.
1. If the phase difference is greater, then the tap on L1 can
be changed to put the B7 RF amplifier in phase.
2. Typically, more of the inductor will be shorted out for
the Binary amps than for the Big Steps.
3. Do not reduce Efficiency coil turns to less than 1/2 of
the given Frequency determined value.
n. Continue to check the phasing on the remaining binary
amps. Note that the amount of active turns on the Effi-
ciency coils will tend to be less on the smaller binary steps.
5.7.9.2
Binary Amplitude Alignment
The output of the Binary RF amplifiers can vary from frequency
to frequency. To optimize the linearity of the modulation signal,
the output amplitude of the Binary RF amplifiers can be varied
in 5% increments. Triangle or ramp modulation must be used for
this procedure.
a. To check the Binary alignment, operate the transmitter at
5 kW output with 10%, 100 Hz triangle modulation.
b. Connect the external sync input of the scope to the output
of the generator.
c. On the scope, display the demodulated output of the modu-
lation monitor.
d. Expand the vertical and horizontal display to view the
positive going portion of the ramp.
e. Connect the other channel of the scope to the Modulation
Encoder gold jumper for Big Step RF amplifier RF37.
f. Raise or lower the modulation until a transition from 0.0
to 5.0 Volts can be seen on the Step 37 display. From this
display it is possible to see at which point in the modulation
ramp Step 37 is being turned on.
g. Move the scope probe to the Modulation Encoder signal
for Step 38.
h. Raise and lower the modulation until Step 38 can be seen
to turn on. A small transition in the demodulated waveform
may be noticed where a big step turns on. See Figure 5-11.
i. By making small changes in both the power level and
modulation level, it should be possible to display the
demodulated ramp between two big steps. This is the area
to look at for binary alignment.
j. If the binary alignment is proper, the transitions between big
steps will be smooth. If, for instance, the 1/2 Step, B7,
amplitude is too low, you will see a transition approximately
halfway between Step 37 and Step 38. This is the half step
transition. You may also see that there is now a transition
at Step 37 and Step 38 also. See Figures 5-11 and 5-12.
WARNING
ENSURE ALL PRIMARY AC POWER IS REMOVED FROM TRANS-
MITTER AND THAT A GROUNDING STICK HAS BEEN USED TO
DISCHARGE ANY RESIDUAL POTENTIAL WHERE POWER HAS
BEEN APPLIED BEFORE PERFORMING THE FOLLOWING
STEPS.
k. Determining which binary step amplitude is not lining up
with the others can take some trial and error.
1. For example, to change the binary amplitude for the 1/2
Step, open the interlocked inner door.
2. Remove the 1/2 Step RF amplifier B7 and Big Step RF
amplifier RF33.
3. Look through the slots of the removed amps and move
J30 on the motherboard to the next desired position.
4. Reinsert the modules and check the ramp linearity.
5. Repeat for all Binary Steps B7 through B11 using J31,
J32 and J33, if necessary. Binary RF amplifier B12 does
not have amplitude adjustments.
NOTE
The ramp may not appear to be perfect, even at what appears to
be optimum binary alignment. This is because the displayed ramp
is at LOW power at around 10% modulation.
CAUTION
ENSURE THAT THE BINARY JUMPER PLUGS ARE PROPERLY
INSERTED AND SEATED. A LOOSE OR MISSING JUMPER WILL
CAUSE BINARY TOROID DAMAGE.
5.7.10
Other Adjustments
These adjustments should normally not change during a fre-
quency change, but it is advisable to check their setting for
optimum transmitter performance.
5.7.10.1
Audio Gain Adjust: A35R15
This sets the proper audio modulation level into the transmitter.
Refer to the paragraphs on the Analog Input Board replacement.
5.7.10.2
Offset Adjust: A34R75
This control adjusts the Modulation Tracking of the transmitter
or, in other words, how equally it will modulate at different power
levels. Refer to the paragraphs on the Analog to Digital Converter
replacement procedure.
5.7.10.3
Dither Adjust: A35R43
This control reduces the small modulation steps caused by the
Digital Modulation process. Refer to the paragraphs on the
Analog Input Board replacement.
5.7.10.4
Modulated B- Adjustments
This signal optimizes the switching time of the PA Modules and
affects high frequency distortion and response. Refer to the
paragraphs on Analog Input Board and DC Regulator replace-
ment for B- adjustments.
DX-25U
5-20
888-2297-002
Rev. Z1: 06-02-00 Additional info to ECN 46105
WARNING: Disconnect primary power prior to servicing.
