Nautel XL12, Technical Instructions

Page: 61 / 238

12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 2-37
01 January 2002
(k) Adjust output of audio generator for a 90
percent modulation depth indication on the left
plus right (L + R) channel of the station's
stereo modulation monitor. Ensure the left and
right signals are equal.
(l) Adjust active RF drive PWB's
IPM BAL
ance
(R20) and exciter interface PWB's
IPM GAIN1
potentiometers for minimum left/right
separation, as indicated on the station's stereo
modulation monitor.
(m) Re-adjust the exciter interface PWB's IPM
GAIN2 potentiometer (R4) to optimize the
left/right separation, as indicated on the
station's stereo modulation monitor.
(n) Select exciter B. Press/release EXCITER B
switch, noting its integral lamp turns on.
(o) Set audio generator's output to zero (turned
off).
(p) Select exciter B. Press/release
EXCITER B
switch noting its integral lamp turns on and the
EXCITER A switch's lamp turns off.
(q) Repeat steps (j) thru (o) for exciter B.
2.5.2 RF CURRENT LEVEL
: Select or verify
the resistance values of R3 and R6 on the distribution
PWB have been selected to provide between 1.60
and 1.70 VDC at the anode of CR2, on the
distribution PWB, when the RF output is an
unmodulated 13 200 watts and it is terminated by a
precision 50-ohm load as follows:
NOTE
The values of resistor A16R3 and A16R6 was
selected during manufacture. It should not be
necessary to change/select their value, unless the
distribution PWB is replaced or tuning of the RF
output filter is changed.
(a) Terminate or verify the RF output is terminated
into a precision 50 ohm, resistive, 20kW
dummy load.
(b) Turn off or verify the modulating audio source
is turned off.
NOTE
The distribution PWB (A16) is located behind the
exciter panel, on the left hand side of the
transmitter (see figure MD-1). Refer to figure
MD-12 for its assembly detail.
(c) If a replacement distribution PWB is being
installed and the values of R3 and R6 in the
original distribution PWB are known, install
resistors of these values as R3 and R6.
(d) If a replacement distribution PWB is being
installed and the values of R3 and R6 are not
known, install a 47.5 ohm, 0.25 watt resistor as
R3.
(e) On the distribution PWB, connect a digital
multimeter (preset to measure DC volts)
between TP5 (+) and ground.
(f) Verify the requirements of paragraph 2.4.3
have been completed and are being met.
(g) Set the transmitter for an RF output of 13 200
watts.
(h) Select and install the appropriate resistance
value for R6 to provide a multimeter reading of
1.65 ± 0.05 VDC. Record R6's resistance
value for future reference.
NOTE
Satisfy the requirement of step (h) by substituting
resistor values, noting an increase in resistance
will increase the voltage level.