The portable ATU shown in my You-Tube Video costs less than £15 to build and will handle about 25 Watts depending on the frequency and load. It uses two dual polyvaricon capacitors in a standard Z-Match circuit. The exact value of the polyvaricons is not important, but the dual sections must be equal e.g. 275/275 pF or 335/335 pF is fine, but 140/60 pF won't work properly. You can lower the minimum usable frequency to 1.8 MHz by wiring a switched 470 pF fixed capacitor across the coupling capacitor if desired.
The controls are arranged to maximise the available space and keep the ATU as small as possible.The toroid is held in place by foam packing around the switch. When winding the toroid keep the winding tight and remember that every time the wire passes through the centre of the toroid it counts as one turn regardless of where it starts or ends.I added some tape after winding my toroid to protect the windings, rather than keep them in place.Construction is straight forward, but take your time marking out and drilling the box as it's easy to make a mistake. Good luck with your own construction.
10 Adams Meadow, Ilminster, Somerset, TA19 9DD, England