Powering Telemetry radios externally

The RFD900 Radio Modem is a high powered 900Mhz, ISM band radio modem designed for long range serial communication. Ranges of 15km and much higher have been reported.

Warning Many common flight controllers have telemetry port current limits that prevent directly powering RFD900 radios at their full transmit power. You should power high power radios externally.”