Fred PA0FVH wrote:
Dear group,

As a temporarily solution I would like to use a cheap 5/8, 6/8 or 7/8 WL
commercially available CB antenna as a non resonant vertical with elevated
radials for use on 10 - 40 meters tuned by an automatic remote ATU at the
base of the antenna. I used MMANA and EZNEC (demo) to calculate the expected
impedance for the frequency range and found too many results for the height
of the antenna. Now I am confused about what to select.
Is 5/8WL on 10meters a good height or 8 meter (22')?
What I want is a low take off angle on 20 and 30 meters with high efficiency
and an impedance which my remote ATU can handle.

Fred, PA0FVH


To a first order, you just want to avoid lengths where it's close to a
half wavelength (assuming you're using an ATU that's designed for this
sort of application) because that's where the Z is highest and toughest
to match. The low Z points are going to be easy (a few tens of ohms, and
almost any tuner can do that).

So, the lowest frequency where this is the case is where the wavelength
is 16m... straddling the 15 and 17m bands. In practice, what you might
need to do is adjust the length of the antenna by a few tens of cm one
way or the other to find a place where your tuner is happy.

Another situation is where the antenna is a full wavelength.. but 8m is
higher than the 10m ham band, so you're probably ok.

The other problem is if the reactive component gets too far for your
tuner to handle, but without knowing the tuning range of your tuner,
that's hard to know.