Specifications
through DB7 (MSB) on the input pins U18-11 through U18-4
that comes from the Trim PALS.
When S1 is in the calibrate position and the unmodulated power
output is set to 100 kW, the voltage U4-7 is 1.47VDC and U4-6
is - .64VDC.
If S1 is returned to the Normal position and the Raise control is
depressed and held until the power output is 110 kW, the voltage
at U4-7 is 1.54VDC and U7-7 is -1.28VDC.
If the Lower control is depressed and held until the power output
is 90 kW, the voltage at U4-7 is 1.40VDC and U7-7 is 0VDC.
J.6.7.2 Trim PALS
The eight bit digital word for the digital pot is supplied by the
Trim PALS. They basically function as Up/Down counters with
a reset to center range control. Each PAL has the same program.
U21 is used for HIGH power, U20 for MED, and U19 for LOW.
The operation of each PAL is the same, so only High power PAL
U21 will be discussed.
When the transmitter is on at the HIGH power level, J2-27 receives
a high signal from the Controller. This signal is sent to U21-6 and
activates the PAL, at this time U20 and U19 are inactive.
When the Raise control is depressed, J2-15 receives a high signal
from the Controller. This signal is sent to U21-4 and the PAL begins
to count up in binary fashion until U21-14 through U21-21 are all
high.At this point the poweroutput shouldbe 110 kW and the upper
limit of the Fine Power Control has been reached.
When the Lower control is depressed, J2-13 receives a high
signal from the Controller. This signal is sent to U21-5 and the
PAL begins to count down in binary fashion until U21-14
through U21-21 are all low. At this point the power output should
be 90 kW and the lower limit has been reached.
J.6.7.3 S1 Calibrate
When S1 is placed in the Calibrate position, U21-2 is grounded.
This resets the PAL to the center range, regardless of previous
Raise or Lower commands. U21-14 through U21-20 will be low
and U21- 21 will be high, and the three power levels can be set.
When S1 is switched back to the normal position, U21 is still in
the center range. The PAL can then respond to Raise or Lower
controls.
J.6.7.4 Fine Power Control Bypass
If P6 is moved from 2-3 to 2-1, Fine Power Control is Bypassed.
The previous differential amplifier U4-7 now becomes a non-in-
verting amplifier with the (-) input connected to ground through
R164. Power Step Up and Foldback functions are still active.
Refer to the Emergency Operating Procedures Section VI - A for
the bypass procedure.
J.6.8
Power Control
The output of the differential amplifier is normally connected
through P4 2-3, to distribute the signal to three switches inside
U17. The switch U17 is shown in the transmitter OFF condition.
When the transmitter is turned on at HIGH power, the Controller
places a high (+5VDC) on J2-27. Level Shifters U25-12 and
U14-12 convert the high to +15VDC at U17-11. This causes
switch “A” to close, connecting U17-14 to U17-13. Potentiome-
ter R65 HIGH is now part of a voltage divider along with R76.
Clockwise rotation will raise power output and counter-clock-
wise rotation will lower power output.
When the transmitter is turned on at MED power, the Controller
places a high on J2-29. Level Shifters U25-10 and U14-10 apply
a high at U17-10. This causes switch “B” to close, connecting
U17-15 to U17-1. Potentiometer R67 MED is now part of a
voltage divider along with R76. Clockwise rotation will raise
power output and counter-clockwise rotation will lower power
output.
When the transmitter is turned on at LOW power, the Controller
placesa high on J2-31. LevelShifters U25-8and U14-8apply a high
at U17-9. This causes switch “C” to close, connecting U17-4 to
U17-3. Potentiometer R66 LOW is now part of a voltage divider
along with R76. Clockwise rotation will raise power output and
counter-clockwise rotation will lower power output.
J.6.8.1 Power Control Bypass
If P4 is moved to the Bypass position 2-1, the Bypass Power
Level pot R68 remains in the voltage divider circuit regardless
of the power level.
Refer to the Emergency Operating Procedures Section VI - A for
the bypass procedure.
J.6.9
Output Amplifier
The output of the power control voltage divider is connected to
the (-) input of Output Amplifier U8-2. Summed together with
the (Audio + DC) is a small Dither signal on the (+) input U8-3.
The output of U8-1 -(Audio + DC) is connected to J3-5 where it
continues on to the A/D Converter board.
J.6.10
Modulated B- Drive
The output of U8-1 also is fed to the (+) input of amplifier U8 at pin
5. The (-) input of U8-6 is a positive voltage, adjustable with
OFFSET control R104. The output of U8-7 is an audio signal with
an adjustable DC offset. The signal passes through a Non-linearity
circuit formed by several resistors and diodes. The purpose of this
network is to reshape the waveform to control RF Amplifier turn
on/off times on the Modulation Encoders.
When the -(Audio + DC) output of U8-7 is small (corresponding
to a negative modulation peak), changes in the voltage result in
roughly proportional changes in the voltage at the output.
As the -(Audio + DC) output becomes more negative (corre-
sponding to a positive modulation peak), it is clipped more and
more heavily and changes in the output of U8-7 result in much
smaller changes in the voltage at the input to U10-6 and in the
Modulated B- supply output voltage.
The output of the predistortion network is connected to single
ended to balanced amplifiers at U10-6 and U10-3. This balanced
output signal at U10-7 and U10-3 (J1-3 (+) and J1-1 (-)) goes to
each Modulation Encoder where it modulates a negative supply
to provide the Modulated B- Supply.
J-4 888-2339-002
WARNING: Disconnect primary power prior to servicing.