ADS-B; A GUIDE TO CONNECTING GPS-DEVICES, ADS-B RECEIVERS, MODE-S TRANSPONDERS AND DISPLAYS...page 5
TRANSMITTING DATA...ADS-B OUT
ADS-B OUT is created by connecting a GPS-source to the mode S transponder. The GPS must provide the position in NMEA-format. The data must be as pure as possible, excess data (air data, Flarm, hardware-settings etc.) must be filtered out. Basically the GPRMS-sentence is all that is required for this purpose, all other data may create confusion or poor communication between GPS and transponder. In this chapter we discuss connecting GPS-sources to the EASA-certififed mode S transponders available for gliders and other light aircraft.
Before we continue please take note of these important messages:
SET THE GPS SIGNAL INTEGRITY LEVEL IN THE TRANSPONDER TO THE LOWEST SETTING UNLESS A CERTIFIED GPS IS USED!
The manual for the Garrecht VT01 only dictates that the input of NMEA data must have a baudrate of 4800 bps and it must be supplied at pin 3 of the 9-pin Sub-D plug (pic 11). The VT01 transponder is set by default to a low GPS signal integrity, so no changes are required. We recommend connecting the GND from the GPS and the transponder.
The TRT800 by default comes with a 15 pin external memory connector (pic 12). De port setup indicates that port 12 is to be used for NMEA input for ADS-B OUT.
PLEASE NOTE: This is a certified part of the instrument!
However, nowadays the standard delivery includes a cable-set (TRT800EMRS) which provides a dedicated 9 pin Sub-D connector (pic 13) attached to the external memory connector for RS232-communication with the transponder. In this connector, pin 3 should be used for the ADS-B OUT data. For GPS input in standard NMEA format (GPRMC) teh baudrate should be 4800bps.
The Trig transponders accept NMEA data over pin 5 of the 25-pin connector (pic 14). Baudrates can be set to 4800, 9600 or 19200 bps at setup. Also make sure to select the proper GPS System Integrity Level value. During setup you can indicate that an ADS-B receiver is installed. Only select YES if you have a certified ADS-B receiver (so in most cases the selectiong should be NO)! We recommend connecting the GND from the GPS and the transponder.
A slightly different procedure is in use for the Becker BXP640X transponders:
Two 25-pin connectors can be found on the backside of the units: P9 and J8. P9 is the connector needed to connect a GPS (pic 15). If a GPS receiver is used pin 2 (GPS-Enable) should be connected to the aircraft DC supply ground. The RX-port of the transponder can be found on pin 9 of the P9-connector and pin 8 should be grounded. GPS receiver power supply may be connected to pin 6 if its current consumption does not exceed 1A. The Becker transponders are capable to operate with GPS receivers which provide GPGGA and GPVTG NMEA-sentences at a baudrate of 4800 bps. Other compatible GPS-receivers are: FreeFlight System GPS/WAAS 1201, NexNav miniGNSS, Garmin GNS 430 and 530.