This does not have to be as complicated as transmitterdan implies.
With ferrites on the cables
, and capacitors shunting to ground/negative, you are creating a low pass filter. You can do this with ferrites alone or capacitors alone, but they will work even better in concert. Mix31 ferrite toroids and 0.1 mFd (plus or minus an order of magnitude) RF capacitors will do this with a frequency cutoff low enough that spurious HF signals will be suppressed. No complex calculations are needed for this application.
If it is the control head
creating the noise
, you want the ferrites and capacitors on the cable as close to the head
as possible. If it is the main unit, you will want them on both the power leads AND the cable going to the control head as close to the main unit as possible.
Very strange that your Spectra is radiating but others don't have the problem.
Let us know how it all turns out.