Garmin GTX 3000 Manual

Manual Transmitter Tuning

1. Power down the unit and connect the antenna port to a Mode S / ATCRBS interrogation
generator (SDX2000 or equivalent) through a cable with 1.5 ± 0.1 dB loss.
2. Set the interrogation generator for ATCRBS interrogation at 100 PRF and power level of -50
dBm.
3. Connect the UUT output from the interrogation generator to the oscilloscope input. The
oscilloscope port should be set for 50 ohm impedance, or should have an external 50 ohm
load connected if using a high impedance setting.
4. Refer to Error! Reference source not found. for locations of the alignment components
referenced in the steps that follow.
Figure Error! No text of specified style in document..1. Alignment Point Locations
5. Adjust the screws on trimmer caps C1027, C1024, C2020, C2035, C2025, and C2017
clockwise until resistance is felt, then 4 turns counterclockwise.
6. Adjust potentiometers R2012 and R2003 fully counterclockwise, then turn clockwise one
quarter turn.
7. If not connected, reconnect the ribbon cable between the transmitter and main boards.
8. Turn on the unit power.
9. Using the GTX3000 SI Tool, put the unit in test mode.
10. Reply pulses should be seen on the oscilloscope. If not, adjust the scope vertical scale and /
or trigger level until a stable pulse display is obtained. The actual vertical scale settings are
dependent on the characteristics of the interrogation generator UUT output.
11. Adjust the horizontal scale on the oscilloscope to 200 nS per division to display a single
pulse.
12. While observing the pulse on the oscilloscope, adjust trimmer cap C2017 for maximum pulse
amplitude.

GTX 3000 TX Tune Procedure