40~10m L-Network Matchbox
Here is a schematic of a simple, yet versitile Antenna Matchbox that can be used with high or low impedance antennas, simply by switching the side of the coil that the capacitor(s) connect to.
Note: it can be used on 80m by increasing the inductance from 10uH to about 15uH.
Note: Instead of a roller inductor, you can use a tapped coil with a band switch.
In that case you will have to determine the position of the taps emperically.
And here is the link to the page with the choke-balun.