Acom ACOM2100 Operating Manual page 13

If you use more than one antenna per band, it is necessary that you select the proper
antenna BEFORE the next step. Retune after selecting a different antenna for the
same band, since the impedances may differ substantially (unless their VSWRs are
excellent, i.e., below 1.2:1 for both).
Do not switch the BAND switch knob while transmitting with the amplifier! Such hot
switching will eventually destroy the band switch, and this is not covered by the
warranty!
When tuning, do not apply continuous drive longer than one minute and after that
pause 1-2 minutes for tube cooling.
We recommend that you tune-up at the center frequencies of the preferred frequency band. First, select
the band switch and the correct antenna number (never with RF applied!). Then, use table 4-1 in order
to achieve an approximate preset for both TUNE capacitor and LOAD capacitor knobs:
b) Selecting the plate-load True Resistance Indicator (TRI) tuning aid.
You may select the TRI scale in three different ways:
- By briefly pressing simultaneously the PREV+NEXT buttons. This will insert a 6dB attenuator between
the driver and the amplifier's input (the ATT LED will light), removing the need to reduce the drive power
during tuning. Press PREV+NEXT buttons momentarily again to switch the attenuator out of the input
circuit and to return to the earlier screen. If you use any of PREV or NEXT buttons, the attenuator will
be switched off too, but the information screen will change.
- By pressing repeatedly either the PREV or NEXT button until you reach the TRI scale. This will not
insert the attenuator, so you must be careful to use less than 20W drive (unless the amplifier is near
correct tuning); otherwise the next step will be executed automatically:
- By simply applying a normal (50-85W) drive level while the amplifier is not yet tuned. This will
automatically invoke the TRI tuning aid and will insert the input attenuator (the ATT LED will light) after
one second. The attenuator will be switched off, and the old screen will be returned automatically, after
PTT is released. If near-optimal tuning is achieved, the attenuator will not be inserted again. If the old
screen was unchanged (TRI, selected manually earlier), it will be possible to precisely tune the amplifier
at nominal power without changing drive at all. Use this approach to shorten the tuning process duration.
c) Tuning Procedure.
While a continuous carrier (CW key down, RTTY or FM) signal at the desired frequency is still applied:
- Look at the upper scale (forward power); obtain maximum power using the upper (TUNE) knob;
N O T E
C A U T I O N
C A U T I O N
Band, MHz Tune Knob Dial
1.8 - 2
3.5 - 4
7 - 7.3
10.1 - 10.2
14 - 14.35
18 - 18.2
21 - 21.45
24.9 - 25
28 - 29.7
50 - 54
Table 4-1. Approximate tuning preset
Load Knob Dial
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