I like my old Ten-Tec AT-5(?)
It is just a coil and dual capacitor arranged as a parallel
tuned circuit with the center tap of the capacitor grounded.
There is a link coil of a few turns that couples to the
coax, two leads with croc clips to adjust where the
capacitor connects to the coil, and two more croc leads
to set the taps for the output terminals. I've used it
on all sorts of single wires and balanced lines. It doesn't
work as well with very low impedance loads, though, and
the coil taps are too far apart for convenient use on
15 and 10m. But you could build your own with more
convenient taps and an option to open the center of the
coil for series tuning.
There are many tuner designs, depending on the range of
impedances you want to match. If you are going to match
coax with a high SWR then the standard T tuner is a good
choice as it can match low impedances with reasonable
sized capacitors. (An SWR of 10 : 1 on 50 ohm coax means
the impedance at the tuner could be as low as 5 ohms.)
End-fed wires have a limited range of impedances to
match: you won't find a 5 ohm load without a lot of
capacitance, so you can design the tuner accordingly.
There is an excellent design by Ulrich Rhode DJ2LR in
QST (December 1984 I think?) that used a standard L
network following a 4 : 1 stepdown transformer, so it
always matched from 12.5 ohms up to the load. With the
addition of a fixed capacitor and coil to the normal
variable ones this gave a very wide range unit including
160m.
Here are some other tuner designs you can try:
http://www.xs4all.nl/~pa0fri/ATU/Anttuners.htm#EJust about any of the commercial T-network tuners will
work for what you want with reasonable efficiency. (Or
you can build your own.) That is a good choice for
a single tuner with a wide tuning range, which is often
the case with antenna experimentation. Once you find an
antenna that you like you can build a preset custom
tuner for it and free up the variable one for other
experiments.
