Nautel XL12, Technical Instructions

Page: 47 / 238

12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 2-23
01 January 2002
2.3.5 AUDIO PASS BAND SELECTION:
The interphase PDM driver PWBs (A1A5 for
exciter 'A' and A1A6 for exciter 'B' on the exciter
panel) have provision to select one of four audio pass
bands. Refer to the interphase PDM driver PWBs.
The selection is determined by the settings of their
AUDIO FILTER
switch (S1). The user must determine
the most suitable roll-off frequency from the four
choices tabulated in table 2-3 and then set the
AUDIO
FILTER switch for each PWB accordingly. The
factory default selection is for a -1.0dB roll-off at the
highest frequency. This selection will be adequate
for most installations.
NOTE
A 3-pole Butterworth filter that can be altered
towards a pseudo-Bessel response is used as the
low-pass audio filter.
The decision to select a lower roll-off frequency
will be dictated by complex factors. They may
include an antenna with sideband limitations,
square wave overshoot, and the processing the
audio is subjected to. In some instances, AM
stereo stations may wish to reduce/eliminate pass
band influence. Nautel's field service department
will provide advice and recommendations based
on the installation.
(a) Refer to table 2-3 to determine the roll-off
frequencies that can be selected and the
settings of the
AUDIO FILTER
switch that are
required to obtain them. Record the selected
roll-off frequency and the
AUDIO FILTER switch
settings for future reference.
(b) Set or verify the AUDIO FILTER switch, on both
interphase PDM driver PWB's, has been set to
provide the desired high-frequency roll off, as
recorded in step (a).
NOTE
The optimum variable pulse duration modulation
frequency
(
ƒ
PDM
)
was selected during factory
tests. Refer to the Transmitter Configuration
Sheet
,
provided with the Factory Test Results , to
determine switch settings that were established to
obtain this frequency. These settings should be
used unless the assigned carrier frequency is
changed.
Table 2-3 Audio Pass Band Selection
HIGH FREQ AUDIO FILTER
ROLL-OFF SWITCH SETTINGS
(-1.0 dB) S1-1 S1-2
16.0 kHz CLOSED CLOSED
13.5 kHz OPEN CLOSED
10.5 kHz CLOSED OPEN
7.5 kHz OPEN OPEN
2.3.6 AUDIO CHOICES:
The AUDIO SOURCE
switch on the exciter panel's interface PWB must be
set to reflect the type of audio and number of audio
inputs that are applied to the transmitter. Paragraph
2.1.6 identifies the audio input options which are
available.
2.3.6.1
Refer to paragraphs 2.1.6.1 thru 2.1.6.4 to
identify which exciter/audio input option is in use and
then set or verify the exciter interface PWB's
AUDIO
SOURCE
switch has been set to the setting identified
for that option.
2.3.7 REMOTE CONTROL CHOICES:
Remote control input circuits must be configured to
reflect the type of inputs that are applied to them.
Paragraphs 2.1.8 and 2.1.9 identify the functions that
can be controlled remotely and what their connection
options are. Refer to paragraphs 2.1.8.1 thru 2.1.8.6
and 2.1.9.1 to identify which remote control inputs
are being applied and then determine which are
connected to apply a differential input and which are
connected to apply a single-ended input.
2.3.7.1 Differential Inputs:
Install a 2-socket
shunt post in the
DIFFERENTIAL INPUT
position (pins 1
and 2 shorted) of the 3-pin header identified as being
associated with each control that applies a
differential input.
2.3.7.2 Single Ended Inputs:
Install a 2-socket
shunt post in the
SINGLE ENDED INPUT
position (pins 2
and 3 shorted) of the 3-pin header identified as being
associated with each control that applies a single
ended input.