Automatic Level Control (Alc) - ELECRAFT KPA1500 Owner's Manual

2. To make the KPA1500 switch from
either
KEY IN
connected between the KPA1500
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
a) If you are not sure of the SWR, press and hold the
LED lights).
b) Tap ATU TUN E
tune cycle.
4. Tap the M OD E
5. Apply a few watts of RF drive and watch the
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
the output indicated by the
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
8. When driving the KPA1500 with an Elecraft K3
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 or K3, program
S
each band. See Per-Band Power Control in the Owner's Manual for further details. (Requires
K3 /K3 firmware version 4.82 or later).
S
If you use the AUX cable interface between the K3
or Figure 5, page 16) and you have
This means you can set two per-band power levels with the K3
when it is in OPER
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
The Elecraft K3 and K3 ALC intentionally have a slow attack and much slower decay to avoid adding more
S
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.
STBY
pulled low (contact closure to ground) or with the optional KPAK3AUX cable
AUX
ATU M OD E
to initiate a tuning cycle. Apply 25 to 50 W of transmitter drive during this
switch as needed so the
POWER (W)
CONFIG:POWER SET
OPER
mode and another for pass-through transmitting when the KPA1500 is in
.
or K3
PWR SET-PER BAND
S
to transmit, it must be in
connector and the K3
switch to put the ATU in bypass (
ATU M OD E
OPER LED lights.
POWER (W)
bargraph
SWR
bargraph increases.
or K3, use the per-band power control to set the
S
to
Per Band
or K3 and KPA1500 (Figure 4, page 15
S
set to K3
RADIO TYPE
/ STBY status to the K3
function to set proper drive levels, not ALC.
21
OPER mode and keyed. Use
/K3 ACC connector.
S
BYP
switch to enable the ATU (
bargraph illuminate to indicate RF
indicates less than 1.5 while
FAN SPEED MIN
and adjust the power level for
or K3, the KPA1500 will send the
S
or K3.
S
or K3. One to drive the KPA1500
S
LED lights).
IN
menu setting.
STBY . The