David Forsyth wrote:

After doing a lot of reading on the web about long wires, short wires,
inverted L's, impedance matching, baluns, ununs, onions, fundip, and who
knows what else...

I was thinking (run for cover please)

Couldn't one simply use a small active device to buffer the straight wire
antenna at the end where it tethers to Ye Olde Oak tree or whatever it's
tied to? I was thinking you could even make it powered with a small gel
cell or something and a solar cell to power it. Some sort of wide-band
amplifier that would have a suitably high input impedance to accomodate the
higher and varying impedance of the wire over the desired frequency range,
and yet having a fixed 75 or 50 ohm output impedance to drive the coax that
runs back to the house. Then you could use a transformer in the house at
the receiver if it's the type that wants to be fed from a high-impedance. I
would think this would get around the problem of an impedance matching
transformer mismatching the antenna on frequncies where the antenna
impedance drops significantly. Also it could provide perhaps some minimal
gain to boot. Some of those commercial impedance matching transformers sell
for over $50 US. So I would think a small buffer amp might not be too
cost-ineffective.

Dave

If you want to put a preamp near the antenna, you can run a DC
voltage up the coax by using RF chokes in the DC lines at both ends to
isolate the RF, and series coupling capacitors to block the DC. That is
how LNA/B/Cs are powered on most Sat TV receivers, and I have used it at
60 KHz, as well. You could use a Minicircuits chip that cost about
$1.00 by adding a couple caps, a coil and a resistor. Their ERA or MAR
series would do a good job, and the part is cheap enough that you can
afford to replace it when lightning takes out your preamp. I have some
rejected blank surface mount PC boards that will work for the part (They
were laid out wrong, and engineering had to eat the cost). You can also
do dead bug, or even use the old Vector Perfboard pins or standoffs and
build it point to point. They do need a ground plane, but are quite
stable.

These parts have a 50 ohm output, so they will match either 50 or 75
ohm coax with little problems. You might need a low pass filter to
remove out of band noise and signals to prevent overload, or if you want
to have real fun built a remote tuner at the preamp.
--


Michael A. Terrell
Central Florida