5902 Bell 202 Modem Hardware Manual
October 19, 2007
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6
Maintenance
This module requires no routine maintenance. If the module is not functioning correctly, contact
Control Microsystems Technical Support for more information and instructions for returning the
module for repair.
6.1
Gain Adjustments
The 5902 modem has two gain adjustments potentiometers. There is one gain adjustment jumper.
Refer to the
5902 Module Layout
figure for the locations of the adjustment potentiometers and
jumpers.
6.1.1
Transmitter Adjustment
The TX GAIN potentiometer (R19) adjusts the transmit output level. The range of adjustment is
determined by the TX GAIN jumper (J3). It permits an adjustment range of 0 dBm to –20 dBm, or a
range of –15 dBm to –35 dBm.
The transmit level is factory adjusted to 0 dBm. This is the recommended level for telephone lines
or hard wired installations. The level may be reduced for use with radios or other systems requiring
a lower output level.
We recommend the 5902 transmitter output level be maintained at its maximum level, to ensure the
highest possible signal to noise ratio, wherever possible. Some radios require a lower input level.
Use the radio input level adjustment to adjust the signal where this is possible. Where this is not
possible, lower the 5902 modem transmit level.
The transmit level is calibrated with a 600 ohm load. If there is no load on the transmit output, the
level is 6 dB (2 times) higher. Thus, the factory adjusted level is +6 dBm with no load. Connect a
600 ohm resistor across the output to lower the level by 6 dB.
6.1.1.1
0 dBm to
–20 dBm Range
Install the TX GAIN jumper (J3) in the bottom position (0 dBm) to select the 0 dBm to –20dBm
range. This position is recommended for applications that require maximum signal levels for proper
operation. This is the factory default position.
Adjust the output level with the TX GAIN potentiometer.
6.1.1.2
–15 dBm to –35 dBm Range
Install the TX GAIN jumper (J3) in the top position (–15 dBm) to select the –15 dBm to –35 dBm
range. This position is recommended for radios that require low receive signal levels for proper
operation.
Adjust the output level with the TX GAIN potentiometer.
6.1.2
Receiver Adjustment
The RX GAIN potentiometer (R18) adjusts the receiver gain. It has been factory adjusted for a
carrier detect level of –30 dBm. It may be adjusted by +/- 10 dBm if necessary.
6.2
Modem Test Modes
The TST switch selects the modem test mode. There are three basic tests provided as described
below. The TST switch must be open for normal modem operation.
