thank you for fast reply.
I planed to buy FrSky DIY TX module to be installed in my Turnigy 9x and compatible FrSky RX on the multicopter, now I have to consider the xbee too, or it would be ok with the new 3DR sistem ?
If I get the 900MHz will be ok with my 2.4GHz TX and my 5.8GHz vTX ?
Anyway I think the FrSky will still be good as it will also alert me when my TX link will be weak.
Yes, 900Mhz is a good fit with those other devices.
It seems I must go with 433MHz as the 900MHz is used for GSM in Europe ..