Nautel XL12, Технические инструкции

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12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 5-12
01 January 2002
(c) Place a short circuit between TP4 and ground
on the RF drive tuning PWB.
(d) Remove the connector from E1 on RF drive
amplifier 'A' (A11A1) and connect an RF
generator between the wire and ground. Set
the RF generator to the transmitter carrier
frequency.
(e) Monitor the output of the generator with an
oscilloscope and frequency counter and adjust
the RF drive tuning inductor A11L1 for a null in
voltage on the oscilloscope.
(f) Confirm the circuit is tuned by sweeping the
frequency generator below and above the
transmitter carrier frequency and confirming a
null at the correct frequency.
(g) Remove the test equipment.
(h) Install the connector on E1 on RF drive
amplifier 'A' (A11A1).
(i) Restore the connections on relay assembly
A11A7 by moving the push-on connectors
from pin 1 to pin 4 and pin 3 to pin 6.
(j) Remove the short circuit between TP4 and
ground on the RF drive tuning PWB.
5.5.21.2 RF Power Module Tuning:
The RF
power module tuning procedure ensures the RF
power modules are tuned for optimal operation in the
host transmitter. Tune the RF power modules as
follows:
(a) Operate the transmitter into a 50 ohm dummy
load at a power level of 1000 watts without
modulation.
(b) Monitor the RF current being applied to power
module A with a DC multimeter connected to
TP5 'A'.
NOTE
An RF power module that has a failed RF
amplifier cannot be tuned. Repair module before
performing this procedure.
(c) Using the screwdriver (Nautel Part# HAZ79)
from the transmitter ancillary kit, adjust RF
power module A's RF drive tuning inductor for
a minimum reading. Refer to the RF power
module service instruction booklet for location
of the RF drive tuning inductor.
(d) Repeat steps (b) and (c) substituting the
correct RF drive tuning PWB test points and
RF power modules.
5.5.21.3 RF Drive Level:
The RF drive level
procedure ensures the correct 22 volt peak-to-peak
RF drive voltage is applied to the RF amplifier FETs
and the RF drive level detector threshold is properly
set.
(a) Turn off the transmitter and remove an RF
power module as described in paragraph 5.6.
(b) Place the RF power module on a work bench
and carefully remove the black plastic cover
from an RF amplifier.
(c) Place an oscilloscope probe on the gate lead of
Q6 in the RF amplifier. Refer to figure MD-6
in the RF power module service instruction
manual for the RF amplifier's assembly detail.
(d) Re-install the RF power module in the
transmitter as described in paragraph 5.6.
(e) Operate the transmitter at 1000 watts output
power level from exciter A. Set the
EXCITER
CONTROL
switch on the control interface PWB
to
AUTO TRANSFER INHIBIT
.
(f) Adjust the
VOLTAGE CONTROL
potentiometer
on the exciter A RF drive regulated power
supply A11A5 until a reading of 17.7 volts
peak-to-peak is recorded on the oscilloscope.
This is the lowest allowable RF drive voltage.
If the power supply cannot be adjusted low
enough to achieve 17.7 volts peak-to-peak,
adjust it to its lowest voltage.
(g) Adjust the RF DRIVE THRESHOLD potentiometer
on the RF drive tuning PWB until the
transmitter
EXCITER RF DRIVE
alarm just turns
on.