21
2.
To make the KPA1500 switch from
STBY
to transmit, it must be in
OPER
mode and keyed. Use
either
KEY IN
pulled low (contact closure to ground) or with the optional KPAK3AUX cable
connected between the KPA1500
AUX
connector and the K3
S
/K3 ACC connector.
3.
If you have a 50 Ω dummy load or an antenna that you know presents a low SWR to the
KPA1500, press and hold the
AT U M O D E
switch to put the ATU in bypass (
BYP
LED lights).
a)
If you are not sure of the SWR, press and hold the
AT U M O D E
switch to enable the ATU (
IN
LED lights).
b)
Tap
AT U T U N E
to initiate a tuning cycle. Apply 25 to 50 W of transmitter drive during this
tune cycle.
4.
Tap the
M O D E
switch
as needed so the
OPER
LED lights.
5.
Apply a few watts of RF drive and watch the
POWER (W)
bargraph illuminate to indicate RF
output power.
6.
Normal drive levels to produce the full 1500 W output will be about 50 W but start with a much
lower level to observe how the KPA1500 behaves.
7.
Slowly increase the drive power and confirm the
SWR
bargraph
indicates less than 1.5 while
the output indicated by the
POWER (W)
bargraph
increases.
During heavy use, you may hear clicking sounds as amplifier components heat and cool.
This is normal. The rear panel fans will turn on and increase speed as needed automatically. If
desired, you can keep the fans running at all times using the
FAN SPEED MIN
menu setting.
8.
When driving the KPA1500 with an Elecraft K3
S
or K3, use the per-band power control to set the
amplifier output just below the desired peak output on each band. Do not rely on ALC to control
the power output, see below.
In the K3
S
or K3, program
CONFIG:POWER SET
to
Per Band
and adjust the power level for
each band. See
Per-Band Power Control
in the Owner’s Manual for further details. (Requires
K3
S
/K3 firmware version 4.82 or later).
If you use the AUX cable interface between the K3
S
or K3 and KPA1500 (Figure 4, page 15
or Figure 5, page 16) and you have
RADIO TYPE
set to K3
S
or K3, the KPA1500 will send the
OPER
/
STBY
status to the K3
S
or K3.
This means you can set two per-band power levels with the K3
S
or K3. One to drive the KPA1500
when it is in
OPER
mode and another for pass-through transmitting when the KPA1500 is in
STBY
. The
transceiver will automatically return to your preset power levels as you switch the KPA1500 between
OPER
and
STBY
.
Automatic Level Control (ALC)
Automatic Level Control (ALC) is a useful safety mechanism, but do not use ALC as the principle power
control
.
Doing so causes many of the unwanted transmit dynamics you often hear on the air including excessive
intermodulation distortion (IMD) and clicks.
Elecraft recommends using the K3
S
or K3
PWR SET-PER BAND
function to set proper drive levels, not ALC.
The Elecraft K3
S
and K3 ALC intentionally have a slow attack and much slower decay to avoid adding more
distortion or dynamics problems than necessary. However, not all of the negative effects of ALC action can be
avoided. It is still best to set the ALC threshold and then adjust the RF drive from the transceiver to avoid ALC
action in normal operation.
