The output from the DigiLite modulator section is very low, typically 1 or 2mW, and one or two stages of amplification will be required to get to the 150-200mW input required by the RA18H output brick (500mW for dual version). A MMIC followed by a more powerful amplifying device such as RF2126 is a typical arrangement, some lower power bricks or even an under-driven RA18H brick can be used as a driver.(with suitable attenuation). It is important not to overdrive the input to the RA18H, not only to avoid unwanted distortion of the ultra-linear digital signal, but also to avoid permanent damage to the first stage of the brick. There are a number of Ebay shops supplying suitable kits, search for 'rf amplifier'. MiniKits in Australia have a useful collection of amplifier kits. A browse through the BATC Forum will also reveal a number of useful links If you are handy with homebrew pcbs you might try this design from 9H1LO.
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