Auto Tune Sub-Menu - Acom 2000R Operating Manual

4-1. AUTO TUNE sub-menu

a) Let us examine the difference between the two types: DEF- and USR- tunings.
DEFault tuning settings are permanently available in your amplifier memory. They are normally used
when the load VSWR at the input end of the feed line is very low.
Real loads often have VSWR greater than 1.5:1, which usually requires the use of an outboard antenna
tuner. Your amplifier will perform the functions of an automatic antenna tuner for VSWR less than 3:1,
or 2:1 on 160m if you prepare USR (User) tunings. This is a fully automatic procedure of matching the
real load to the optimum tubes load.
User tuning settings are memorized and stored in a nonvolatile memory. They will be retrieved
automatically each time you change the operating frequency or antenna number as described in the
previous section. This will enable you to use the amplifier without an outboard antenna tuner over a
wider frequency range and to change frequencies and antennas faster than would otherwise be possible.
The amplifier is capable of memorizing up to 10 different antenna tunings for each frequency segment.
User tuning settings are identified with the identifiers A1 to A9 and AM, irrespective whether they are
for different antennas or for different environment conditions (for example wet and dry weather on
the same antenna).
REFLECTED POWER readings and the measured VSWR depend on the load
impedance only and not on the amplifier tuning. If the impedance is different from
the nominal (50 Ohm pure resistive), the REFLECTED POWER bargraph will always
indicate the reflected power presence (even at actual USR-tuning). The proper USR
tuning will, however, allow you to operate with greater power without distortions
and danger to the amplifier.
The real power in the load is equal to the difference between the FORWARD- and REFLECTED-
bargraph readings. For instance, at indicator reading for FORWARD 1775W, and for REFLECTED 275W,
the real output power is 1500W. At very high VSWR (lack of antenna or shortened antenna), the
FORWARD and REFLECTED readings will be almost equal, while the real output power (the difference
between them) will be practically zero.
The amplifier can operate safely if the following rule is obeyed: "REFLECTED POWER < 500W". Matching
can be assured for loads with VSWR up to 3:1 (for 160m - 2:1). Nevertheless, for some loads matching
is possible even at higher VSWR.
Using a feeder of coaxial cable at VSWR > 3:1 on HF bands is not recommended.
At such high values of VSWR, the high voltages, high currents, and heat associated
with line losses, risk permanently damaging the coaxial cable.
Always prefer USR- to DEF-tunings and update them periodically, in particular when you install a new
antenna or when a significant change in the environment occurs (snow, ice, newly appeared or removed
massive objects, power lines etc.) that would cause significant changes in the antenna impedance.
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