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c. Depress the HIGH power button. If HIGH power was

previously set for 25 kW, the transmitter output should now
be approximately 25 kW.

d. Depress the RAISE button until the power output reaches

30 kW or stops raising.

1. If the maximum power output is less than 30 kW, adjust

R27 for 30 kW output.

2. If the power output exceeds 30 kW, adjust R27 so that

the transmitter power will not exceed 30 kW.

5.6.2.3

Offset Adjustment: R84 (Modulated B-)

a. Connect a scope to the modulated B- output at A30 TP30

of the DC Regulator.

b. Operate the transmitter at 5.0 kW and modulate 100% with

a 100 Hz sine wave.

c. Set up the scope at 1.0 Volt per division to measure a dc

coupled audio waveform. You should view a distorted sine
wave of approximately 2.0 Vp-p on a -3.0 VDC negative
offset. See Figure 5-7.

d. Adjust R84 so that the positive peak of this waveform just

begins to clip, then back off the control slightly. Note that
the waveform will reach the clip point as it moves more
positive. This positive peak of audio corresponds to the
modulation envelope negative peak.

5.6.2.4

Audio Gain Adjust: R15

The Audio Gain Adjust is normally factory preset for 100%
modulation with an audio input level of +10.0 dBm. It can be
adjusted for 100% modulation with audio input levels from -10.0
dBm to +10.0 dBm. To adjust:

a. Operate the transmitter at the desired output power and

slowly increase the output of the audio generator to the
desired level.

b. Adjust R15 for 100% modulation.

c. The RF output may vary when adjusting this control. Once

R15 is adjusted, the power output may need to be reset with
the RAISE and LOWER buttons.

5.6.2.5

Dither Level Adjust: R43

The Dither control is preset and there should be no need for
readjustment. If it is desired to check the setting of the control,
use the following procedure.

a. Operate the transmitter at approximately 1.0 kW output

and modulate with a 100 Hz tone at 95%.

b. Use a scope to display one cycle of demodulated audio

from the modulation monitor.

c. Expand the vertical sensitivity of the scope to display only

a portion of the waveform.

d. Adjust R43 maximum counterclockwise. At this point it

should be possible to see some of the individual Digital
Modulation voltage steps. (It may be possible to see the
steps better at a lower modulation level, but it may also be
necessary to externally sync the scope with the audio
generator).

e. While observing the individual steps, adjust R43 clock-

wise until the individual steps can no longer be distin-
guished. This should occur within two turns of R43. Ad-
ditional clockwise adjustment of the control may appear
to further smooth out the steps but will result in additional
noise on the waveform.

f. Only increase the Dither Level enough to just smooth out

small step transitions. Other, slightly larger, steps or
glitches will be seen at low power and modulation levels.
This is normal. Do not use R43 to try and smooth these
out. Never use more than three clockwise turns of R43.

5.6.3

Oscillator (A17)

Preset the replacement board before installation by placing all
jumpers in the same positions as in the board to be replaced.
These are identified in Table 5-2.

a. Set S1, a four section DIP switch, to the same setting as

the board to be replaced.

b. Adjust the tuning slug of L4 with a non-inductive tuning

tool for approximately the same amount of penetration into
the coil.

c. Remove the heater assemblies from crystals Y1 and Y2. An

angle bracket bolts to the PC board and holds the crystal
heaters in place.

d. Carefully remove the crystals and reinstall them on the new

board. Install the heater assemblies on each crystal.

5.6.3.1

Carrier Frequency Adjust: C1/C3

a. Select crystal oscillator and heater Y1 by moving jumpers

J1 and J6 to position 1-2.