FrSky FUL-1 TX Module & Receiver Upgrade Adaptor
The FUL-1 is basically a level converter that allows you to upgrade the firmware of the FrSKY telemetry DFT/DJT/DHT V1 transmitter modules and also the D8R V1 receiver to provide the following additional features:
Four different tones corresponding to four alarm sources
Improve the smoothness of servos when working with D8R
Provide two PPM modes: HS (9ms) if using high speed digital servos and FS (18ms) if using analogue servos.