what frequency does it operate and what are the intensity of the harmonics

The UC3843 datasheet shows the typical oscillator frequency as 100 kHz with a maximum of 500 kHz.   All the "ZVS" modules I've seen are set to run at 75 kHz.    Neither fundamental or harmonics are present at the output but as I noted,  magnetic coupling can occur.  I verified that by using my favorite "direction finder" receiver that tunes the LF and BC bands - no noticable difference in the reception of an AM BC signal was heard unless I put the loop antenna very close to the power supply, and then it was a broadband racket, not a single tone.   Nothing was heard on any harmonic either, and a spectrum analyzer showed no peaks with .5,  2, and 10 MHz span.

In the time domain, scoping the output does show noise spikes,  depending on when I captured the waveform I could get just about any frequency but I captured the 300V and 12V signals where the scope thought the fundamental was the strongest frequency to measure.  

Here is the HV output measured via a 100X probe with 300VDC and a 60ma load:

And here's what the 12 input looked like:

Remember these boards only have 10uF of output filtering, which is good enough to filter the PWM residue from DC but additional high frequency bypassing is a good idea.   Good old filtering and shielding...

73, Bob W9RAN