2.12.5
VSWR Foldback And VSWR Fault Check Out
This exercise involves using the exciter as a source for forward
and reflected power samples in order to test for proper VSWR
foldback operation and fault detection.
It is recommended that you read and understand this procedure
and that you make notes of the original jumper positions and
cable connections before starting.
2.12.5.1
Visual
a. Depress and hold both exciter LOWER buttons for 15
seconds to ensure minimum output.
b. Connect visual exciter output to J6 on the back of the main
controller.
c. Temporarily remove the remote I/O cable on back of the
exciter to enable the exciter without running the transmit-
ter.
d. Slowly raise visual exciter power until the bar graph on the
master controller display indicates 100% visual power.
e. Move the cable now at J6 to a spectrum analyzer and set a
reference level. Reconnect the cable to J6.
f. Connect the aural exciter output to the analyzer and set the
level 26 dB less than visual.
g. Connect the aural exciter to J8 on the Main Controller.
h. The VSWR should read approximately 1.11:1. If substan-
tially different from this reading, perform procedure in
paragraphs 5.11.1 through 5.11.3.1 as required to adjust
the reflected power calibration.
i. Set Visual foldback jumper J18 to connect pins 2 and 3
(disabled).
j. Slowly raise the aural exciter power.The VSWR FAULT
lamp should illuminate at approximately 1.4:1. R51 ad-
justs the threshold of the VSWR FAULT lamp.
k. LOWER aural exciter power. Reinstall J18 to pins 1 and 2
(enabled).
l. Slowly raise aural power until FOLD BACK ACTIVE
lamp just comes on.
m. Note the visual VSWR reading. It should be approximately
1.2:1. R20 adjusts the visual foldback threshold.
2.12.5.2
Aural
a. Depress and hold both exciter LOWER buttons for 15
seconds to ensure minimum output.
b. Connect visual exciter output to J7 on the back of the main
controller.
c. Temporarily remove the remote I/O cable on back of the
exciter to enable the exciter without running the transmit-
ter.
d. Slowly raise visual exciter power until the bar graph on the
master controller display indicates 100% aural power.
e. Move the cable now at J7 to a spectrum analyzer and set a
reference level. Reconnect the cable to J7.
f. Connect the aural exciter output to the analyzer and set the
level 26 dB less than visual.
g. Connect the aural exciter to J9 on the Main Controller.
h. The VSWR should read approximately 1.11:1. If substan-
tially different from this reading, perform procedure in
paragraphs 5.11.1 through 5.11.3.1 as required to adjust
the reflected power calibration.
i. Set Aural foldback jumper J19 to connect pins 2 and 3
(disabled).
j. Slowly raise the aural exciter power. The VSWR FAULT
lamp should illuminate at approximately 1.6:1. R63 ad-
justs the threshold of the VSWR FAULT lamp.
k. LOWER aural exciter power. Reinstall J19 to pins 1 and 2
(enabled).
l. Slowly raise aural power until FOLD BACK ACTIVE
lamp just comes on.
m. Note the Aural VSWR reading. It should be approximately
1.4:1. R33 adjusts the Aural foldback threshold.
NOTE
Reconnect exciter remote I/O cable when done to restore correct
operation of the protection circuits. Verify that all forward and
reflected samples are properly reconnected.
2.13
Initial Application of RF Power
2.13.1
Visual
a. For systems with multiple visual PA cabinets (20 kW and
up), refer to the factory test data for initial setting of the
phase control for the Phase and Gain module. Place switch
on the phase and gain module in the SET position. Set the
A and B gain pots fully clockwise.
b. Check that aural and visual AGC modules are on.
c. LOWER the exciter to minimum drive and apply a ramp
or staircase test signal.
d. Press transmitter ON pushbutton.
e. Check to see that all RF amplifier modules are enabled.
f. Slowly raise visual power while observing VSWR, FOR-
WARD POWER, and, in a multiple visual PA cabinet
system, REJECT POWER. Stop at approximately 25%
forward power. In some cases where transmitter power is
significantly less than 30 kW, the PA modules used in the
drive chain may illuminate only half of the green LED even
though RF drive is applied.
g. Phase and Gain module alignment: For systems below
20 kW, skip the following procedure. 20 kW and 30 kW
systems have only one phase and gain module, so the
procedure is performed only once. In 45 kW systems,
perform this sequence on the lower level (A / B) phase and
gain module, then proceed to the top level ([A+B] / C)
module. In 60 kW systems, begin with the (A / B) and (C
/ D) phase and gain modules, then proceed to the top level
([A+B] / [C+D]) module.
1. Adjust phase and gain module INIT phase control in
SET position for minimum reject power.
Section II - Installation
Rev. C: 8-24-2000
888-2365-001
2-9
WARNING: Disconnect primary power prior to servicing.
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