I'm trying to build a setup for the 3$\omega$ technique, and the equipment is making my brain hurt. When I send a signal directly from the function generator to the lock-in, it only measures about 71% of the input However, the lock-in accurately reads the voltage from its own sine-out, and the amplitude of the output from the function generator was checked on an oscilloscope. I am baffled as to what is happening here.
It also reads 0 voltage on the third harmonic, which I'm not sure is supposed to happen either. If anyone has done 3$\omega$ experiments before and could advise me on how to get this set up correctly it would be much appreciated.