Pulsar LPA100, Системное руководство

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Page 5–2 June 2001
50W / 100W Linear Power Amplifier System Manual Technologies, Inc.
the chassis, measure between the INPUT
and COMMON front panel test points.
Since all four of these amplifiers’ inputs are
tied together the signal level will be the
same. Set the level at this point to
0.67Vrms (+9.5 dBm, 50
Ω
reference) by
turning up the INPUT LEVEL pot on the
driving carrier set’s Power Amplifier
module. This level should never exceed
1Vrms (+13.0 dBm, 50
Ω
reference) in
order to prevent overdriving the LPA. Also
this level is approximately 20 dB lower
than the level coming from the driving
carrier set’s output since there is a 20 dB
attenuator on the backplane input of the
LPA chassis. The driving carrier set should
be keyed to its maximum output power
(high level keying) if it has a 1W/10W
setting when setting the above 0.67 Vrms
level.
6. Next, read between the red and purple test
points (50W output) on the 50W Power
Combiner module and the level should be
at /- 1V (141Vpp or +47.0 dBm
+/- 0.3dB, 50
Ω
reference) which is equal to
50W output for a 50
Ω
load. If this level
needs to be slightly changed, then adjust
the driving carrier set amplifier’s INPUT
level potentiometer again. Then recheck
the level on the INPUT test point of one of
the 12.5W Power Amplifiers to make sure
it doesn’t exceed 1Vrms as set in the
previous step. It is recommended that the
50W output level be measured with an
oscilloscope to verify the accuracy of the
selective level meter and also to check that
the output sine wave is not distorted. This
is important because a 6.2Vrms or 1 dB
difference in level is equal to being off by
13 watts.
7. Finally, measure between any one of the
50W Power Combiner’s four input test
points (orange, yellow, blue, & white - see
Figure 5-1) and the input common test
point (black) in order to verify that the
levels are equal to one another and approx-
imately 26Vrms (41.3 dBm, 50
Ω
reference). If not then go to the calibra-
tion/troubleshooting procedure in Section
5.2 for instructions on adjusting the indi-
vidual 12.5W Power Amplifiers. It is
important that these 4 levels be equal to one
another, but the absolute value of 26 Vrms
is not very important.
8. This concludes the adjustment of the
LPA50.
5.1.2 LPA100 Adjustment Procedure
1. Verify proper connections per the connec-
tion diagram, Figure 5-3. Terminate the
output of the LPA100 (coax connector J9),
that would normally connect to the line
tuner, with a 50
Ω
non-inductive resistor
rated at 100W.
2. Turn the INPUT LEVEL potentiometer on
the driving carrier set’s Power Amplifier
module to minimum (fully counterclock-
wise). This will prevent it from overdriving
the LPA when initially powered up.
3. Turn on all four Power Supply modules one
at a time noting that both the INPUT and
OUTPUT red LEDs come on for each
Power Supply module. If all the power
supplies are not turned on within a few
minutes of one another, the Power
Combiner module(s)’s balance resistors
will heat up which is normal since only part
of the Power Amplifier modules would be
energized causing imbalance in the Power
Combiner module. This heating will
disappear after all Power Supplies are
turned on and all the Power Amplifier
modules are energized.
4. On any one of the four 12.5W Power
Amplifiers in each of the two chassis,
measure between the INPUT
and
COMMON front panel test points. Since all
four of these amplifiers’ inputs are tied
!
CAUTION
BE CAREFUL TO NOT LET THE TEST POINTS
SHORT TOGETHER SINCE THEY ARE PHYSI-
CALLY CLOSE TOGETHER.