I've had good luck with link coupled, parallel resonant matching circuits, for single band EFHW antennas. I followed the design laid out on this person's website for designing the match box.
http://www.aa5tb.com
On the left side of the page there are a few links that cover EFHW antennas. I used a decent sized #2 (red) iron powder toroid with somewhere between 1:7 & 1:8 turns ratio (1:49 to 1:64 impedance). I can't find my notes page at the moment, but I think it was 3:22 or 3:23 turns, my apologies. I then have an air variable cap across the secondary of the toroid transformer to resonate out the transformer's inductance. The air variable has range for 40, 20, 17, and 15m, but I only have 40m and 20m wires that I use with it. Each band has its own counterpoise cut to 0.05 of a wavelength as explained here: http://www.aa5tb.com/efha.html
That page also describes tuning the capacitor on the bench with a resistive load, then adjusting the length of your antenna to get the best match without moving the capacitor. After the wire is trimmed to resonance any remaining small mismatch can be tuned out by slight tweaking of the variable.
Be mindful of the voltage rating of the variable capacitor at higher power levels. The RF voltage across the secondary can get very high due to the higher impedance.
I have my 40m and 20m wires mounted horizontally about 25 feet of the ground at my house and they work well for the low height. I'd prefer to have them vertical, but I don't have anything talk enough to do that at my house.
This type of box is great for portable use also. If you have your different wires already trimmed to length, you can quickly throw one up into a tall tree and be in the air in minutes.
73 - Brad
