Richards,
The MFJ-956 and MFJ-16010 tuners are both intended for use with random
length wire antennas... not loops. MFJ does make loop tuners. The
MFJ-933 and -935 but they are not Z-match designs. Those tuners are
meant to be mounted at or _very_ close to the loop.
Using any tuner remotely located from the loop (including the Z-match)
will distort the loop pattern since the feedline becomes part of the
loop. With close-spaced wire like speaker cable there will be greater
signal loss than with wider spaced wire like 300 Ohm twinlead or 450
Ohm ladderline. I follow a very loose rule of thumb that says the loop
circumference should be a minimum of 4 times the length of the
feedline. That seems to ensure that the loop does not simply act like
a short circuit at the end of the feedline. The greater the loop
circumference the more signal capture area it will have... and that's
the name of the game. The tuner is simply used to enable a reasonably
efficient transfer of that energy to the receiver.
The Z-match is not difficult to build. Mine uses one 365pF variable
cap, 1 dual-365pF variable cap, the coil wound on a T80-6 toroid and a
DPDT switch to choose between the two output link windings. I believe
I used the design on G3YCC's web page as a guide. The whole thing is
build into a black plastic enclosure from Radioshack. The caps and
toroid were ordered from Ocean State Electronics.
It's certainly much cheaper to build one of these than to buy an MFJ
tuner... and, IMHO, it's much more flexible in use for receiving. I
have used mine for transmitting also but the caps limit power handling
to a max of about 5 watts.
73,
'Bear' NH7SR
