Dear Erik,
Looking again at your screenshots, I think the last one where you increased the separation to 4khz actually shows the two fundamentals, but not of equal amplitude. An intermod scan would show the two original frequencies of equal amplitude with a symetrical ?diminishing ¡°comb¡± of intermod products either side of the fundamentals, spaced at the difference of the two fundamental frequencies (every 4khz).
steve L
