The optional echoUATmux harness allows echoUAT to support a GTX327/GTX330 with a separate serial altitude encoder. Icarus, Garmin/Trimble, Northstar, Magellan formats are currently supported. The harness allows plug and play connectivity to aircraft previously wired for the Navworx ADS600EXP with the Garmin 327 and 330 transponders. The echoMUX can still be used if you did not previously have a Navworx system. If you have the Garmin GTX327 or GTX330 transponder PLUS a serial altitude encoder you can use this harness. The echoMUX has a male DB9 connector on it so you will need to supply a female DB9 for the wired connections to the transponder and the altitude encoder.