The GPA-9 A version is designed for mounting in a standard 19–inch rack cabinet using the 3U panel
provided. Four screws (not provided) are required to attach the panel to the rack sides. This panel also
serves as a heat sink for the PA module, and is normally mounted with the cooling fins facing outward.
The GPA-9 B version uses a smaller heatsink (intermittent duty) but has the same 4 mounting screws.
Place the amplifier module in service by making the following cable connections.
1. Using low loss 50-ohm coaxial cable, connect the RF Input connector (J101) to the RF output
connector of the MDS SD9 radio.
2. Using low loss 50-ohm coaxial cable, connect the RF Output connector (J100) to the station
duplexer or antenna.
3. Connect 10-16 Vdc power supply (13.8V nominal) to the Power connector (J102). The outside pin
is positive (+); the next is negative (–).
Adjusting RF Power Output
To check/set the amplifier's RF power output, proceed as follows.
1. Connect a wattmeter (rated for use at 900 MHz, and at least 40 watts) to the amplifier's RF
output connector (J102).
2. Terminate the wattmeter into a 50-ohm, non-inductive load.
3. Set SD9 PWR=30dBm. (+27 to +30dBm is allowed)
4. Apply RF drive from 900 MHz radio and note the RF power indication at J100.
5. If necessary, adjust R138 (see Figure 2) with an insulated flat blade tool to achieve the desired
output level. Access to this control is available near the RF input connector
If the flange temperature of the active device in the PA exceeds recommended limits (90C) the PA bias will
be automatically removed reducing output power. At this time the GREEN LED will be ON at the same
time as the RED LED when the unit is in transmit. When temperature falls within limits normal operation
GPA-9 will automatically reduce output power if a high VSWR is detected.
2.1 Mounting the Unit
2.2 Connecting the Unit
3.3 Alignment (Setting power output)
3.4 Overtemperature Fault
3.5 VSWR Fault