Several years ago I investigated potentiometers with the lowest possible reactance up through 30 MHz. I found the Allen Bradley TYPE J and specifically a 1 k ohm P/N JA1G044P102B exceptionally good.
This pot demonstrated a range of R from nearly a short circuit to 1 k which moved EXACTLY along the real axis on the Smith Chart display of my VNA; swept through 30 MHz. I was amazed of the low parasitic reactance displayed. I'll see if I can find one to sweep and display.
Alan
