One of the weekly newsletters I receive mentioned an interesting application note from Maxim: Adapting Low-Band ISM Transmitters for High-Band Operation.
It is about adapting a 434 MHz transmitter to work on the second harmonic 868 MHz. Both frequencies sit into license-free bands in most Countries and are harmonically related, like many of our HAM bands.
The article talks about how those simple transmitters work (25% duty cycle switching PA), how their output looks like, how clean their output is, how to redesign the matching network and to do some noise measurements maths.
These chips can deliver about 13dBm/20mW (10dBm/10mW on the 2nd harmonic after proper matching): not much power for E.M.E., but enough for a simple beacon in a tiny (SOT-8) 8-pin package.
I found it a good (morning) reading, packed with well explained design information.