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BASIC BOARD MODULE (BBM)
7-4
7.3 BBM ALIGNMENT PROCEDURES
7.3.1 INTRODUCTION
The module is designed to operate at a maximum
input level and maintain that level without added
distortion or noise levels significantly different from
the maximum input level. The overall distortion
should be less than 5% with noise less than -45 dB, C-
message weighted. Adjustments at the maximum
level are difficult due to possible higher distortion and
clipping of the signal, therefore, an average level is
used for alignment. A voice application typically uses
an average level that is -12 dB from the maximum
level. When the module(s) are pre-aligned with the -
12 dB average level, the only adjustment necessary is
to set the input and output levels to the -12 dB level.
The module contains operational amplifier stages
with gain that require the absolute alignment level to
be lowered by the gain of the op amp stage. The
module op amp stages have a +9 dBm output swing.
Since the alignment level is -12 dB from maximum,
the absolute average alignment level would be -3 dBm
for a unity gain op amp stage.
The module contains a PCM CODEC chip that
converts the analog audio to digital and back to
analog. The maximum input of the codec is +6 dBm
absolute level since there is a gain of 3 dB in the
circuitry and the output stage can handle +9 dBm
absolute level. The +6 dBm input level requires the
average alignment level to be lower than a -6 dBm
absolute level.
7.3.2 ALIGNMENT
The basic module is pre-aligned with a tone of
1004 Hz at -12 dBm with a 600 ohm driving imped-
ance. The -12 dBm level is verified by measuring the
level across the interface with a high impedance
balanced AC voltmeter. The main audio levels of the
module relative to the input are adjusted to provide
pre-alignment.
1. Set the module for pre-alignment. Refer to the
Alignment Points Diagram Figure 7-2.
a. Inject 1004 Hz at -12 dBm at EQU of Rx input J1.
b. Jumper J27, pin 2 to pin 3.
c. No personality card attached with P33, pin 1
jumpered to pin 2 and pin 3 jumpered to pin 4.
d. Close S1, section 3.
e. Open S1, sections 1, 2 and 4.
f. Set S5 for test 1, open section 1; close sections
2, 3, and 4.
g. Reset the module, press S2 and release.
2. Main Rx Audio input level from J1.
a. Setup for alignment as in Step 1.
b. Adjust R41 to -6 dBm
±0.5 dB at J11.
c. Verify the level at TP5 of the CODEC to be
-6 dBm
±1 dB.
3. Main Rx to FSK input from J1.
a. Setup for alignment as in Step 1.
b. Close S1, section 2.
c. Adjust R102 for -12 dBm
±1 dB at TP8.
d. Open S1, section 2.
4. Main Tx Audio output level from J1.
a. Setup for alignment as in Step 1.
b. Adjust R83 for a -6 dBm
±0.5 dB at TP3.
c. Adjust R44 for a -12 dBm
±0.5 dB at J12.
5. FSK Output
a. Set S5 for test 8. Close sections 1, 2 and 3, Open
section 4.
b. Reset the module, Press S2 and release.