Nautel XL12, Технические инструкции

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12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 2-34
01 January 2002
(e) Set the output level of the audio signal
generator to zero (turned off).
(f) Select exciter A. Press/release EXCITER A
switch noting its integral lamp turns on and the
EXCITER B switch's lamp turns off.
NOTE
If a C-QUAM AM stereo exciter is installed as
exciter A's RF drive source, proceed to
paragraph 2.4.6.2 unless it is to be checked
when it is set for monaural operation.
(g) Repeat steps (a) thru (e) for exciter 'A', paying
particular attention to the caution about
adjusting the interphase PDM driver PWB's
AUDIO GAIN
potentiometer if a C-QUAM AM
stereo exciter PWB is exciter A's RF drive
source.
(h) Turn off the RF power stage. Press/release RF
OFF switch noting its integral lamp turns on and
the RF ON switch's lamp turns off.
(i) Disconnect the audio signal generator from
TB2-8(+) and TB2-9(-) on the remote
interface PWB.
2.4.6.2 Modulation Checks (AM Stereo
Output):
Verify the RF carrier is being phase
modulated by the L-R audio and it is being amplitude
modulated by the L+R audio when a C-QUAM AM
stereo exciter is installed as exciter A's RF drive
source and exciter A is active.
(a) Select or verify exciter A is selected. Press/
release
EXCITER A switch noting its integral lamp
turns on and the EXCITER B switch's lamp turns
off.
(b) Turn off or verify the RF power stage is turned
off. Press/release
RF OFF
switch noting its
integral lamp turns on and the
RF ON
switch's
lamp turns off.
(c) Set the exciter interface PWB's AUDIO SOURCE
switch to its STEREO position.
(d) Interface an audio signal generator to the left
and right audio inputs of the C-QUAM AM
stereo exciter PWB using a test audio
switching circuit as defined in the exciter's
service instruction manual.
(e) Set the C-QUAM AM stereo exciter PWB to
produce an AM stereo output. Set its
STEREO
ENABLE switch to the STEREO position.
(f) Turn on the RF power stage. Press/release RF
ON switch noting its integral lamp turns on and
the
RF OFF
switch's lamp turns off.
(g) Check the function of the C-QUAM AM
stereo exciter PWB. Refer to the
Maintenance
section of its service instruction
manual, noting:
- Final testing and adjustments are completed
with the transmitter operating into its antenna
system.
- The RF drive output must not be disabled by
disconnecting the RF drive coaxial cable from
the C-QUAM AM stereo exciter PWB's
RF
DRIVE connector unless it is necessary to trouble
shoot the PWB or a complete functional test is
to be completed.
NOTE
It will be necessary to inhibit the automatic
exciter changeover if the RF drive from the C-
QUAM AM stereo exciter PWB is disabled. Set
the system control PWB's
Exciter Control
switch
(S19) to the
AUTO XFR INHIBIT
position.
(h) On completion of testing, turn off the RF
power stage. Press/release
RF OFF
switch
noting its integral lamp turns on and the
RF ON
switch's lamp turns off.
(i) Disconnect the test audio switching circuit
(including the audio signal generator) from the
left and right audio inputs of the C-QUAM AM
stereo exciter PWB.
2.4.6.3 Modulation Peak Limiting:
Verify the
modulation peaks are limited, to reduce RF power
amplifier stress current, when the RF output's
modulation envelope contains low frequency (long
duration), high amplitude peaks, as follows:
(a) Verify the requirements of paragraphs 2.4.6
and 2.4.6.1 have been completed.
(b) Connect an oscilloscope between the
associated interphase PDM driver PWB's TP3
and ground.