It looks like your results are about what is expected. The next step is to
transform your 6 ohm Z to around 50 ohms. As stated, probably a small shunt
coil across the coax side of the loading coil will do the trick. Just wind a
coil, and experiment with turns, probably less than or much less than 10 turns
an inch or two in diameter, which will give you 50 ohms. This will shift the
resonant frequency slightly, so adjust the loading coil again if necessary, but
the shunt coil probably still ok…typically non critical.
I assume you are using insulated wire…pvc…??. If so this will slightly
degrade performance. Your turns are close spaced, slightly better to space
them out slightly, often folks use a string or scrap wire, then after coil is
(glued ?) in place, pull off the spacer wire or string. You will need more
turns, but probably slight improvement. If you really want to get slightly
better performance, use an air core coil, or hold in place with a few plastic
strips, or whatever.
I would just use your existing coil now, use a shunt coil to bring the Z
down, get on the air and enjoy yourself. Later you can design a better coil,
etc. you might gain a dB or so, if you want. I like the shunt coil idea
because it gives your antenna A DC ground, which gives you some static and
lightning protection. Not perfect, for several reasons, and will not protect
you from direct or near direct lightning strikes, so use other measures if that
is a concern.
Rick KL7CW
Sent from Mail for Windows
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