Elecraft KXPA100 Manual - Manual (Page 31)

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If you have a low SWR load attached to the amplifier you may increase the drive to obtain the desired power
output (100 watts maximum). If you have the KXAT100 ATU and need to use it to reduce the load SWR, do so
as described below before increasing power.

Power Output Monitoring: The POWER OUT (W) LEDs light to indicate the power output
from the amplifier. These LEDs light from left to right as a bar of light. For example, 70 watts
output is indicated by the LEDs under 25, 50, 60 and 70 being lit.
The output of power amplifiers typically varies ±1 dB for a given power input. For
example, the amplifier may provide anywhere between 80 and 120 watts output for 5
watts of drive and may vary from band to band. This is typical. Never exceed 10 watts
of RF drive to the amplifier at any time.
ATU Basic Operation
 ATU Modes: The ATU modes are selected by tapping the
M O D E switch.
Bypass (Byp) Mode: The ATU matching network components are bypassed and the output of the
amplifier is routed directly to the selected antenna connector (
ANT 1 or ANT 2 ).
Manual (Man) Mode: When RF is applied the ATU first checks to determine if there is an
acceptable tuning solution in memory for that frequency. If not, a tune operation must be launched
manually. The tuning solution is stored in memory and associated with the antenna connector used,
so you can have a tuning solution in memory for
ANT 1 and a different solution for the same
frequency in ANT 2 to support a different antenna.
Automatic (Auto) Mode: When RF is applied, the ATU first checks to determine if there is a
tuning solution in memory that will result in an SWR of 1.8:1 or less. If not, the ATU
automatically begins a full search for the optimum tuning solution. The tuning solution is stored in
memory and associated with the antenna connector used, so you can have a tuning solution in
memory for
ANT 1 and a different solution for the same frequency in ANT 2 to support a different
antenna.
Preparing to Tune: With the amplifier on, tap the
T U N E switch. The 25/SWR LED under
POWER OUT (W) will start blinking indicating that the ATU is ready to perform a tune operation.
If the ATU MODE was in Byp (bypass) it will switch automatically to Man (manual) mode. The
tune operation can be done in either
Man or Auto (automatic) mode. Tap T U N E a second time if
you wish to cancel the tune operation.
 Tuning: Apply 5 watts from the driving transceiver. You will hear relays click as the ATU finds the
best match and stop when it is done. The 25/SWR LED will continue blinking throughout the tuning
operation and turn off when it is completed. The resulting SWR will be displayed. The SWR is
displayed in the same way as the power output. For example, if the final SWR is 1.5:1 the 1, 1.2 and
1.5 LEDs will be lit. If you are not happy with the SWR, tap the
T U N E switch again within 5 seconds.
The ATU will do a second tune operation using smaller steps in the inductance and capacitance values.
This process takes longer, but may result in a lower SWR.
You may launch a tune operation at any time while RF is applied. The tune operation
will start immediately if RF is present when you tap T U N E or it will start when you
apply RF after tapping T U N E . The amplifier is inhibited during a tune operation, so
only the RF drive from the transceiver will be present at the ATU and antenna connector
until the tune operation is completed.