Acom ACOM2100 - Antenna Selection; Tuning Procedure

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When the Auto Operate function is disabled, the amplier will shift and stay in STBY mode after each
protection trip. To restore operation, the OPER button must be depressed.
When the Auto Operate function is enabled (see S 5-2), the amplier will shift to the STBY mode on a
protection trip. It will return to the OPER mode after about four seconds automatically.
4-3. Antenna change
By pressing the ANT button, the amplier output can be switched between three antenna outputs. The
three lights above the button indicate the current antenna selection. Selection of any of the antenna
outputs can be disabled if not used - see S. 5-3 - Antenna output assignment. This prevents inadvertent
selection of antenna outputs, preventing no-load transmission and possible amplier damage.
C A U T I O N
To avoid damage (not covered under warranty) do not change antennas while
transmitting. Do not transmit into an antenna output (1, 2, or 3) if it is not connected
to an antenna or a dummy load.
4-4. Tuning
Tuning is possible only in operate mode, so you may need to press the OPER button in order to illuminate
the LED above it (unless Auto-Operate is active).
a) Preliminary information.
Tuning the amplier is a procedure of matching the impedance of the currently used antenna to the
optimum tube load resistance. This will ensure optimum plate efciency and RF gain at nominal output
power, with minimum resulting IMD.
Please note, that the REFLECTED POWER readings and the measured VSWR depend on the antenna
impedance only, and not on the amplier tuning. If the antenna impedance is different from 50-Ohm
pure resistive (nominal), the REFLECTED POWER reading will always indicate some reected power
(even with optimal tuning). Proper tuning will assure operation at maximum power without distortion or
danger to the amplier.
Note also that the real OUTPUT POWER in the load is equal to the difference between the FORWARD-
and REFLECTED- readings. For instance, at a reading of FORWARD 1500W and REFLECTED 250W,
the real OUTPUT POWER will be equal to their difference - 1250W (into a 2.4:1 VSWR load). At a very
high VSWR (no antenna or badly mismatched antenna), the FORWARD and REFLECTED readings will
be almost equal, while the real OUTPUT POWER (the difference between them) will be practically zero.
The amplier can operate safely if the following rule is obeyed: "REFLECTED POWER < 400W.” Matching
is assured for loads with VSWR up to 3:1. Nevertheless, for some loads and bands, matching is possible
at even higher VSWR gures. The maximum usable forward power at a VSWR of 3:1 is 1500W with
375W reected. For higher than 400W reected power a ** REFLECTED POWER ** soft-fault protection
trip will occur.
C A U T I O N
Using a coaxial cable with VSWR > 3:1 on HF, and particularly on the 10 and 6
meters bands, is not recommended. At such high values of VSWR, the high voltages,
high currents, and heat associated with line losses risk permanently damage to your
coaxial cable or antenna switch.
Adjust amplier tuning when you change the band or between CW and SSB segments within the same
band. Readjust it each time when you change the antenna, even in the same band, as well as periodically,
even though you may have not changed band or antenna. A signicant change in the environment, such
as rain, snow, ice, new or removed large metallic objects, alien wires nearby etc., can cause signicant
changes in the antenna impedance and an increased VSWR.