"Any USB-to-UART converter, recognisable by OS as COM port. I've tried FTDI, Prolific and SiLabs."

"Maybe it's not connected to anything on APM board, but OSD "shorts" it to GND. If radio detects connection between CTS and GND during startup, it goest to "bootloader mode" for FW…"

"CTS is not necessary, connect as bellow: telem port                radio                                       OSD red                          5v                                          …"

"Show us your setup."

"Connect both radios to PC: - ground module directly to USB, - air module via USB-UART, just like for firmware upgrade process, Open any terminal program (or just 3DR Radio Config Tool and go to "Terminal" option) twice, set proper Com port…"

"Hola Marcin yo no escribo en ingles por eso lo escribi en español, te quiero pedir el favor si me puedes ayudar mis datos de contactro por Skype rolando_falla quedo pendiente saludos"

"Connect air module to USB via FTDI cable and configure with same settings as ground module."

"Better use english language :-)Try to swap Rx and Tx line on "air" side. If you are using module without USB on "ground" side, try to swap Rx and Tx on this side also. Try all combinations. Es mejor utilizar el idioma…"

"https://code.google.com/p/ardupilot-mega/wiki/3DRadio#Duty_Cycle_setting - set this to 0 to make one ground module "listener"."

"Try to short cts and ground on power up again and then immediately press Update Firmware button (try this with both tx-rx combinations, if does't work)."

"Use "Upload Files" link bellow message window."

"Yes, if FTDI is connected right (sometimes Tx and Rx are mixed, it's worth to try to swap them)."

"Pls provide photo of connection FTDI - air module."

"For HM-TRP-433 you can set frequency range 414-454MHz, you have to give a try."

"I suggest to use 868 radio."

"Yes, that's the way 433MHz modules work."