22
If you choose to use ALC, set your transmitter power output correctly (60 W or less) as described under
Transmitting: Initial Steps
and adjust the ALC so it does not affect output power in normal operation.
1.
Drive the KPA1500 to the desired output.
2.
Adjust menu item
ALC THRESH
until power just starts to drop and then set
ALC THRESH
one or two
units above this setting so it does not affect the output power in normal operation.
3.
Repeat on each band.
ALC THRESH
is set and saved separately on each band.
Automatic Antenna Tuner (ATU)
The internal ATU may be used with the KPA1500 in either
STBY
or
OPR
mode. When the KPA1500 is in
STBY
mode, power from the driving transceiver is passed directly to the ATU. Press and hold
AT U M O D E
to select
whether the ATU is active (
IN
) or bypassed (
BYP
). The corresponding LED above the switch will light.
The ATU is active during receive. This may provide a small improvement in signal strength or better rejection of
adjacent bands, due to a more-optimal match between the antenna and transceiver.
The ATU evaluates and decides whether or not it should be active or bypassed. For operating convenience, it
is best to keep the ATU active (
IN
) at all times.
The maximum bypass power through the KPA1500
INPUT
connector is 200 W.
At lower amplifier outputs up to about 800 W, or when using your driving transceiver “barefoot” at 100 W, the
ATU will match loads up to an SWR of 10:1 on 80 through 10 meters and 5:1 on 160 and 6 meters. At 1500 W
the tuner will match an SWR of about 3:1.
High antenna SWR and high output power causes a hard fault and the amplifier will protect its antenna tuner by
going into
STBY
mode.
To prevent or correct this fault, here are some things to try:
1) Check antenna SWR at the desired operating frequency. For example, trying to use a random-
length wire loop on 160 m may be out of range for the ATU (SWR exceeds 3:1).
2) Train the tuner for the antenna and operating frequency.
3) Decrease power to about 800 W. Remember that your feedline may overheat when operated
with high power at high SWR.
Derating graphs for frequency, power and SWR are shown in Figure 8.
