[escherplex]

For experimental Arduino and Rasberry Pi based RF apps, serviceable RF test equipment isn't as cost prohibitive as it once was. EG, Amazon has a PC-based 24MHz - 1.8 GHz RF spectrum analyzer by Touchstone for USD $80. The functional 100 MHz digital Rigol 1102E scope is useful when you're in EE-mode and still runs for $400. If feeling creative, Hantek arbitrary waveform generators hover around $160, and can use Tektronix software available online gratis, complete with GUI. Basic SainSmart USB PC-scopes with logic analyzer modules hover around $150 (watch circuit power output or you can fry your PC). None of these items are top of the line but they should get the job done at the Arduino or Rasberry Pi level.

[makomk]

24MHz - 1.8 GHz... that's going to be a $10 RTL-SDR dongle with some custom software, which doesn't really have a low enough noise floor or intermodulation to test your equipment for compliance. Though proper RF test equipment does seem to have come down in price a lot faster than ham gear.

[escherplex]

True but the projects here are experimental apps limited to 100 mw (theoretically) under FCC Part 15. If you move up to a limited (the old tech minus 5 wpm) Amateur license and start broadcasting at say 50W on 70cm or 23cm then you'll need more sophisticated analytical equipment and software (Clear Waves has a functional kit for $400). As an aside I could never figure out why 13cm became so mainstream in routers, et al, since 2.45GHz is the center frequency of a microwave oven. Looked like a plot to fry the masses /s