There are UHF radio modems that are commonly used for radio telemetry for amateur UAVs (typically RC planes or multi-rotors), transmitting on 900MHz or 433Hz us

There are UHF radio modems that are commonly used for radio telemetry for amateur UAVs (typically RC planes or multi-rotors), transmitting on 900MHz or 433Hz using spread-spectrum technology. Based on HopeRFs HM-TRP module, they present a serial port, either TTL, or as a virtual COM port over USB using a (defacto-standard) FTDI USB to serial chip. You can use two serial, two USB, or one of each - the radio modem in them is identical, it's just the presentation that differs. Line-of-site range depends on the data rate, but is in the region of 1 - 2km, but up to 24km is possible with amplification. The data rate is up to 128kb/s. Lots of technical details can be found on the ardupilot wiki[1]. They were designed as a lower cost, longer range alternative to Xbee [2]. Xbee support ZigBee, multipoint, mesh and other protocols, but not the 433MHz frequency legal in Europe.(900MHz is fine for the US, but the alternative, 2.4GHz, is the same frequency commonly used for spread-spectrum radio-control, so risks interference or reduced range.) They can be purchased in the US for $75 a pair [2]. Clones can be found can be found from Chinese suppliers for less than $40 a pair [3]. [1] http://code.google.com/p/ardupilot-mega/wiki/3DRadio http://code.google.com/p/ardupilot-mega/wiki/3DRadio [2] http://www.digi.com/xbee/ http://www.digi.com/xbee/, http://en.wikipedia.org/wiki/XBee http://en.wikipedia.org/wiki/XBee [3] http://store.diydrones.com/category_s/13.htm http://store.diydrones.com/category_s/13.htm [4] Try: http://RCTimer.com http://RCTimer.com, http://AliExpress.com http://AliExpress.com, http://GoodLuckBuy.com http://GoodLuckBuy.com and search for 3DR