40
40
The 10-40 meter bands on this antenna are tuned the
same way. In this example, we will tune 40 meters.
Tune the rest in the same manner. Bandwidth will
be the only difference as it will increase as you go
up in frequency. 40 will be narrow an 10 will be
wide.
With the antenna in its vertical position on the
temporary mast, check the swr values from 6-7 MHZ.
There should be a sharp dip in the swr value some
where below 7 MHZ. If this is the case then all you
need to do is start trimming the 40 meter spokes to
raise the frequency a little bit at a time. You don’t
have to trim all four spokes to get a result. Trimming
one spoke will change the tuning point. Each time
you find the dip point, write it down before trimming.
this will give you an idea of how much the frequency
shifts for the amount of rod removed. Trimming ½ inch
off each side is a good starting place. Trim the top and the
bottom the same length.
If you don’t see a definite dip point, but rather a vague
dip, then the antenna may be out of balance for that band.
This means the top coil could be electrically different than
the bottom coil. Distance from the ground or proximity
to metal can cause the tuning to shift for each coil. This
can be corrected while tunning an does not indicate a
problem with the antenna or coils. What you are seeing
are two dips that are not on the same frequency. They
combine to form a wide dip around 2:1 swr. We want to
move one of them so that they align with each other. The
easiest way to do that is to move the lower frequency one
until it joins the higher frequency one. Trim either the
top or bottom loading coil. If the dip becomes sharper,
then you must be moving the lower. Keep trimming until
the two dips align and form one sharp dip. Once this is
done, trim each side the same to shift the dip point to the
desired frequency of operation. If you trim one side and
the dip becomes wider or the swr goes up, then change
to the other side and try again. If you make a mistake,
extra 48” rod has been included to create new spokes.
Tune the other bands in the same manner. It is possible
that you may have trouble determining which dip is for
which band. For example, you may see several dips
below 12 meters. To identify which is the 12 meter,
remove one of the 12 meter tuning rods. The dip should
move up in frequency a considerable amount. If it doesn’t
or if it only moves slightly then you have the wrong dip.
COPY RIGH T 2012 MFJ Ente rpri ses Inc.