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User's Manual | ACOM 04AT | Remote Automatic Antenna Tuner and Switch
4. STARTING UP AND MAIN FUNCTIONS
Operating the tuner is straightforward and intuitive due to the high degree of automation.
You may start operating right after installation. However, in order to make a better use of the tuner features,
and to fully adapt it to your particular environment, we recommend reading through the following
information.
4.1. What is tuning type / Rate (Selectivity Degree, Sharpness)
This tuning feature indicates how significant are the changes in the quality of impedance matching between
the antenna and amplifier as a result of small changes of the operating frequency. This determines the
necessary width of the frequency segments required in a band, so that a sufficient degree of matching is
retained within any particular frequency segment. Accordingly, the tuning settings made and stored in the
tuner memory will be usable in a specific frequency segment, narrower or wider, depending on the nature
of the antenna used to do the settings.
In addition to narrowing the frequency segments and, respectively, increasing their number per band, the
high sharpness of tuning generally leads to higher heat losses and greater instability of the settings in time
or due to environmental changes.
It is clear that, by all criteria listed above, it is preferable that the tuning rate (sharpness) be as low as possible,
in order to have a few wide frequency segments, with low heat losses and stable (to external impacts) state
of tuning.
Unfortunately, the tuning sharpness cannot be chosen in a random manner. The specific frequency-
impedance characteristics of each antenna determine a minimum of the tuning sharpness (minimum
Q-factor of the tuned antenna circuit in the tuner), which cannot be further reduced, unless heat loss is
introduced by design (which, however, would lead to lower efficiency).
E.g., antennas with reduced dimensions, often used for 160 m and 80 m, or at higher frequencies, recently,
which are "loaded" with coils close to the maximum current or with "capacitive hats / caps" at the maximum
voltage across the length of the antenna, are normally tuned critically, or "sharply".
The higher the degree of physical reduction of the antenna size, compared to its full-size version, the steeper,
more frequency-dependent, narrow-band and unstable its settings are, in comparison with, e.g., the settings
of a regular dipole. Typical examples include physically short verticals or small-size loops. A poor grounding
of the vertical or the proximity of the loops to the ground may in part reduce tuning steepness, but this is
caused by additionally induced heat losses, and is compensated by reduced efficiency of the emitter.
On the contrary, a full-size, "thick" emitter, or an emitter with a custom-designed shape, such as a Nadenenko
(cage) dipole, an exponential ground-plane or log-periodic structure, will have a much wider usable frequency
band of settings than a regular dipole.
May 2021
S e c t i o n STARTING UP AND MAIN FUNCTIONS | Page 35 of 72
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