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or down buttons . If you don’t have the Automatic antenna selector ACOM 2000S (and ACOM
2000SW remote antenna switch) installed, pushing these buttons would change only the settings
stored in the amplier memory for each antenna.
e) TURNING OFF
In order to turn the amplier off, press the red ON/OFF button on the RCU. If you are not going
to use the amplier for a long time (more than 30 minutes), it is best to turn off the amplier
using the Main Power switch (on the main amplier chassis) as well.
4-2. AUTO TUNE procedure
a) Let us examine the difference between the two types: DEFAULT- and USER- tunings.
DEFAULT tuning settings are permanently available in your amplier 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 amplier will perform adequately with up to a VSWR 3:1, or up to 2:1 on
160m if you prepare USER tunings. This is a fully automatic procedure of matching the real
load impedance to the optimum tubes load. Note: This is NOT equivalent to using an external
antenna tuner and does not change the SWR your transceiver will “see” when the amplier is
in STB mode.
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 may enable you to use the amplier without an outboard antenna
tuner over a wider frequency range and to change frequencies and antennas faster than would
otherwise be possible with other ampliers.
The amplier is capable of memorizing up to 10 different antenna tunings for each frequency
segment, irrespective whether they are for different antennas or for different environment
conditions (for example wet and dry weather on the same antenna).
N O T E
REFLECTED POWER readings and the measured VSWR depend on the load
impedance only and not on the amplier tuning. If the impedance is different
from the nominal (50 Ohm pure resistive), the REFLECTED POWER bargraph
will always indicate the reected 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 amplier.
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 amplier 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.
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