13.
THE USE OF A TUNER
The instructions provided basically discourage the use of a Tuner. This is for the
purpose of initially tuning up the antenna. However there are times when a tuner has
its place.
With the increasing popularity of solid state transmitters a tuner is almost a must.
Back m the days when tube finals were used the manufactures automatically provided
the tuner. Since the solid state circuits have become popular, they have left the tuners
out. This makes it a must for an antenna system to be very critically tuned so the
exciter will not cut back its power.
In
many cases this is very impractical and the use
of a tuner can be a good asset to your set up.
In
tight locations or locations not favorable for an antenna installation, the impedance
of the antenna may not adjust to the 50 ohms needed.
An
installation indoors with a
very short feedline may keep the impedance lower than 50 ohms. The recommended
adjustments may have little affect due to the short feedline. At the lowest the antenna
will exhibit a 20 ohm impedance, giving a SWR of around 3:1. Please keep in mind
that if your SWR is over 3:1 the problem is your resonant point, not impedance value.
This can be corrected by following the instructions on RESONANT POINT.
If
you find isolating the antenna from ground does little to raise the impedance due to
your location, then the tuner can be used to match the exciter to the antenna. This will
not sacrifice performance if done correctly.
Expanding bandwidth is another asset of the tuner. To avoid retuning the antenna for
different parts of the band a tuner can be used to flatten the line and make
it
cceptable to the exciter.
In
conclusion, tuners can be used if not abused in your installation.
Under a conventional installation the Isotron will tune up directly, but many operators
have to operate in less than ideal circumstances. The Isotron was intended for this
challenge and we will be willing to help you with it.
