Several years ago I needed an ASTU for portable use. I built one designed by Louis Varney (G5RV), which is a variation of the traditional Z Match, but using switched coil tappings. His design attracted considerable controversy with respect to potential losses. The view held by some, that the original switchless version is more efficient. The challenge here was squeezing everything into a box that was really too small. Once all the components were positioned there was very little room left. However, I managed it and ended with a very compact unit. Despite the adverse comments about its design, I have always found it has worked well.