Here's an idea ATU for amateur radio reception. It could be used for transmission if air-spaced capacitors and wound inductors are used, but this design uses dielectric capacitors and ferrite toroids. The capacitors are 200 pF types found on eBay - look for variable capacitors.
The inductance values and turns/ferrite are:
3.5 MHz L1 = 8.5uH, 29t T50-1
7Mhz L2 = 1.5uH, 19t T37-2
14Mhz L3 = 0.5uH, 11t T37-2
The powered output is for use with antennas that have built-in amplifiers and need a +ve power supplied over the cable.