Hi Mike,
Another option is to wind a transformer on a toroid with a 3:1 turns
ratio which will give you a 9:1 impedance transformation. If your
antenna has a high impedance,
which an end fed half wave will naturally have, the transformer will
drop the impedance down into the range of your auto tuner. The other
advantages of this are, on other bands where your antenna impedance is
lower your impedance will still be matchable for your tuner. Also, if
you ground the low end of the primary and the secondary windings of the
transformer, it should make your antenna quieter in terms of noise. I
read somewhere that it makes your antenna less attractive to lightning
by not having that positive static charge on it, but I am not sure about
that part. I have an end fed half wave which I like, but I have a
homebrew tuner.
73,
Bob K6GGO
Mike Markowski wrote:
The other day I posted an antenna question about making a K1 antenna
that avoids halfwave multiples (& thanks again to the guys who replied
offlist). From the calculations in that note and some modeling by
another op it seems the ~18m/60' is probably the length to try there.
But end-fed halfwave antennas have some advantages, especially the
fact that as a voltage fed antenna they have less of a need for a low
impedance ground to keep rf losses low. On the other hand, they offer
very high impedance to the tuner. The KAT1 manual says to look out
for "rf problems" at exact half wavelengths but doesn't come out and
say if it can or can't handle it (even if just at certain ranges of
length).
A longtime ham told me some ATUs used to have a switch to move a cap
to one end of the matching network or another to offer a wider
matching range. So if the KAT1 can handle the impedance, great. If
not, maybe I can put a coil in series and tap it at the 50 Ohm point
of the coil. I'm not sure if it's worth the effort, especially since
it'd be nice to keep portable ops as simple as possible. But if
there's a noticeable performace increase... Has anyone tried either
method? (That is, direct connection of halfwave end-fed or tapping an
inductor.) Thanks for any ideas.
73,
Mike ab3ap
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