I put together a video on the basics of making an amplitude measurement, and distortion measurements, of an RF signal on a scope and a spectrum analyzer. The video shows that the amplitude measurement can be made accurately with either instrument provided care is taken to have a common load impedance (and adequate BW of course). The video also shows that it is very difficult to observe harmonic distortion on the scope at levels that would fail FCC emission requirements. In other words, it's always a good idea to include a low-pass filter in your homebrew transmitter designs.
Here's the link to the video if you'd like to watch:http://www.youtube.com/watch?v=XHA4c82msqo
If you like videos like these, you may want to subscribe to my YouTube channel:http://www.youtube.com/w2aew
...and leave me comments regarding what video topics you'd like to see!
Thanks and 73,