Vector-LP Radio Beacon Transmitter Technical Instruction Manual
Page
4-13
Section 4 Testing and Adjustment
Issue 1.1
NOTE
If an external RF generator is producing
the RF drive, verify its output waveform is
symmetrical.
4.3.6.10 EQUALIZING EXCITER GAIN
(Dual Side Transmitters Only)
If the RF output of the transmitter varies
between side A and B, you may need to
equalize the exciter gain. Equalize the
PDM pulse train between sides A and B so
that no change in RF output level occurs
during exciter changeover, as follows:
(a) Go to the Power Module Status menu
(see 3.6.13.2).
(b) Use an oscilloscope to monitor TP17 of
interphase PDM driver PWB A (A6).
(c) On interphase PDM driver PWB A
(A6), adjust the
GAIN TRIM
potentiometer (R31) four turns counter
clockwise and one and a half turns
clockwise. On interphase PDM driver
PWB B (A9), adjust the
GAIN TRIM
potentiometer (R31) four turns counter
clockwise.
(d) Press
RF On
. Increase the
transmitter’s RF output to full rated or
maximum power, whichever is lower.
(e) Use an external current probe to
measure RF output power:
Power = Current
2
x R
load
(f) In the Maximum Output Gain menu
(see 3.6.12.3), calibrate the duty cycle
and forward power as follows:
x
Highlight the value for
Set Duty Cycle
.
Press
Modify
.
x
Change the value to match the positive
duty cycle measured at TP17 in step
(c). Press
Next
.
x
Change the value for
Set Forward
Power
to match the power calculated
in step (e). Press
Done
.
(g) If the transmitter is operating at full
power, go to step (o). If not:
x
Highlight the value for
Maximum
Carrier Reference
. Press
Modify
.
x
Increase the value by 5. Press
Done
.
(h) Repeat step (e).
(i) Set the maximum carrier reference:
x
Record the current duty cycle and
forward power values.
x
Record the power according to the
external current probe.
x
Highlight the value for
Maximum
Carrier Reference
. Press
Modify
.
x
Adjust the value to 1 higher than the
current
Carr. Ref
value. Press
Done
.
(j) Increase the power until maximum
power is reached. Record the power
level on the top line (status bar) of the
GUI display.
(k) Press
Power Increase
and
Power
Decrease
at the same time to set the
RF power to 0 W. Press
RF Off
.
(l) Select side B in the Changeover
Control menu.
(m) Press
RF On
. Ensure all side B RF
power module fans are on.
(n) Press
Power Increase
until you reach
maximum power. Adjust
GAIN TRIM
potentiometer R31 on interphase PDM
driver PWB B (A9) to ensure that the
output power matches the output
power recorded in step (j).
