BASIC BOARD MODULE (BBM)

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.

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