ELECRAFT KPA1500 User manual

ELECRAFT KPA1500
1500-WATT AMPLIFIER
OWNER’S MANUAL
Revision B, May 16, 2018
E740301
Copyright © 2018, Elecraft, Inc.
All Rights Reserved

2
Introduction
On behalf of our entire design team, we’d like to thank you for choosing the Elecraft KPA1500 amplifier.
The KPA1500 offers a unique combination of features. It’s one of the smallest 1500W amplifiers available. The
power supply is in a separate enclosure for ease of station layout.
The KPA1500 is capable of fully automatic operation, yet has an alphanumeric display and a full complement of
front panel switches for precise manual control. A comprehensive remote-control command set is also included.
The KPA1500 can be used with nearly any transceiver, thanks to its instantaneous RF-based band switching,
advanced protection circuitry, adjustable ALC, and extensive parametric monitoring. It also has inputs that
allow direct band switching from many popular transceivers. TR is completely noise-free thanks to the use of
PIN-diode switching.
The KPA1500 comes with a built-in Automatic Antenna Tuner (ATU) that can handle a load SWR up to 3:1 at
the full 1500 watt output in any mode.
Of course, the KPA1500 is an ideal companion for the Elecraft K3Sand K3 transceivers, both physically and
electrically. The Elecraft K3Sor K3 can sense whether the amp is in standby or operate mode, then select the
appropriate per-band power settings. This allows you to set up the K3Sor K3 for “barefoot” operation at one
power level on each band, and then switch the amp to operate and set up optimal drive levels for full 1500W
output. The K3/KPA1500 combination is also capable of extremely fast break-in, especially when the K3Sor
K3 is placed in QRQ (high-speed CW) mode. The two are so well-integrated that you can use the per-band
switches on the amplifier to change bands at the transceiver.
If you use the KPA1500 with both the K3Sor K3 transceiver and P3 panadapter –our new “K-Line” – you’ll
enjoy a high degree of operating convenience, along with world-class performance and the power to get the job
done.
73,
Wayne, N6KR
Eric, WA6HHQ

3
Contents
Introduction...............................................................................................................................................2
FCC-Mandated Part 15 Notice for the Computer Interface Ports ............................................................6
In the Box .................................................................................................................................................6
Installation ................................................................................................................................................7
Positioning the KPA1500 RF Deck and Power Supply ......................................................................................9
Cabling –Power Supply......................................................................................................................................9
Cabling –RF Deck..............................................................................................................................................9
Operation ................................................................................................................................................14
RF Deck Front Panel Controls ..........................................................................................................................14
Power On...........................................................................................................................................................15
Band Switching.................................................................................................................................................15
Antenna Selection .............................................................................................................................................16
Transmitting......................................................................................................................................................16
Using Automatic Level Control (ALC).............................................................................................................17
Automatic Antenna Tuner (ATU).....................................................................................................................18
Amplifier Monitoring and Status Indicators .....................................................................................................21
Remote Operation .............................................................................................................................................23
Fault Conditions................................................................................................................................................24
KPA1500 Utility Program......................................................................................................................29
KPA1500 Firmware Updates............................................................................................................................29
Checking your Firmware Version.....................................................................................................................29
Forcing a Firmware Load..................................................................................................................................29
Wattmeter Calibration Procedure...........................................................................................................30
Specifications..........................................................................................................................................31
Customer Service and Support ...............................................................................................................33

4
Theory of Operation ...............................................................................................................................34
AUX and XCVR Serial Connector Interfaces........................................................................................37
KPA1500 AUX Connector Pinout (DE-15 Male).............................................................................................37
Elecraft KPAK3AUX Interface Cable..............................................................................................................38
Icom Transceiver Interfacing ............................................................................................................................38
XCVR SERIAL Cable ......................................................................................................................................39
TUNE Cable......................................................................................................................................................40
CW Key Tune Cable.........................................................................................................................................41
Yaesu Transceivers ...........................................................................................................................................42
BCD Interface ...................................................................................................................................................43
Kenwood Transceivers......................................................................................................................................43
Flex Transceivers ..............................................................................................................................................43
In Case of Difficulty...............................................................................................................................44
Appendix A—KPA1500 Tuner Frequency Segments............................................................................45
Elecraft manuals with color images may be downloaded from www.elecraft.com.

5
WARNING
Dangerous Voltages are Present Inside the KPA1500 and its
Power Supply
Do not turn on or operate the amplifier or power supply with
the covers off.
Before opening the KPA1500 RF Deck or Power Supply
enclosures:
1. Turn off the KPA1500 by tapping the front panel ON
switch and wait until the fan stops. (The fan drains
the power supply to a safe voltage.)
2. Turn off the power supply breaker switch (on the rear
panel).
3. Disconnect the two Power Supply cables at RF Deck
rear panel before opening the RF Deck enclosure.
4. Disconnect the Power Supply from the mains before
opening the cover.
Key to Symbols, Abbreviations and Text Styles
Important –read carefully
Operating tip
TEMP
Tap switch function (labeled above a switch; press for less than 1/2 second)
PK HOLD
Hold switch function (labeled below a switch; press for at least 1/2 sec. to
activate)
INHIBIT
Typical text appearing on the LCD.
LED
Light Emitting Diode
LCD
Liquid Crystal Display
CAUTION
Follow the instructions under a Caution to avoid damage to the equipment.
WARNING
Follow the instructions under a Warning to avoid serious personal injury.

6
FCC-Mandated Part 15 Notice for the Computer Interface Ports
This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to part
15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in
a residential installation. This equipment generates, uses and can radiate radio frequency energy and, if not
installed and used in accordance with the instructions, may cause harmful interference to radio communications.
However there is no guarantee that interference will not occur in a particular installation. If this equipment does
cause harmful to radio or television reception, which can be determined by turning the equipment off and on, the
user is encouraged to try to correct the interference by one or more of the following measures:
•Reorient or relocate the receiving antenna.
•Increase the separation between the equipment and receiver.
•Connect the equipment to an outlet on a different circuit from that to which the receiver is connected.
•Consult the dealer or an experienced radio/TV technician for help.
Regarding the computer interface: changes or modifications not expressly approved by Elecraft could void the
user’s authority to operate the equipment.
Elecraft Inc.
125 Westridge Dr.
Watsonville, CA 95076
[phone]
www.elecraft.com
In the Box
Included
Item
Reorder Part Number
RF Deck
Power Supply with AC Line Cable
DC Power Cable
E770024
DA-15 Control Cable
E770017
Phono-Phono Key Line Cable
E100416
USB A-B Cable
E980299
Owner’s Manual
E740301
Optional
Item
Elecraft Part Number
KPAK3AUX Cable kit for K3s or K3
KPAK3AUX
Enhanced Mode cable for Flex 6000 series
radios
KXUSB

7
Installation
Installation consists of the following:
•Positioning the KPA1500 RF Deck and Power Supply to provide for proper cooling, see page 9.
•Connecting the KPA1500 RF Deck and Power Supply, page 9.
•Cabling the KPA1500 RF Deck to your other station equipment, page 9.
The KPA1500 RF Deck rear panel is shown in Figure 1. The connectors and controls are described following
the figure.
Figure 1. KPA1500 RF Deck Rear Panel.
and SO-239 RF connectors to antenna system or dummy load.
SO-239 connector for RF input from the driving transceiver.
Low level KPA1500 transmit signal output.
Station ground attachment.
High voltage connection to the KPA1500 power supply.
Control circuit connection to the KPA1500 power supply.
Accepts a 12V input signal for remote control applications to command the KPA1500 to turn on or off. Can
also be connected to K3/K3S rear panel 12V DC OUT RCA connector so the KPA1500 turns on when the
transceiver turns on. See Remote Operation, page 23.
Negative-going voltage for transceivers that require ALC. (Elecraft transceivers do not require this
connection.)
Key Line: Enables the KPA1500 to transmit when grounded. When grounded, the source must be able to
sink 5 mA. 5 VDC open circuit inhibits the KPA1500.
For interconnecting cable to fully integrate the KPA1500 with an Elecraft K3 or K3Sfor enhanced mode
operation.
Input signal to the internal KPA1500 automatic antenna tuner (ATU) that emulates an Icom remote ATU
when the KPA1500 is used with Icom transceivers.
XCVR Serial: Selectable CI-V for Icom®radios or RS232 level information for transceivers such as the K2,
KX2, KX3, Flex Radio, Kenwood and Yaesu transceivers. Radio type is selected in the menu.
Ethernet connection for local or remote operation applications.
USB connection creates virtual COM port for use with the KPA1500 Utility and other computer-based
programs.

8
The KPA1500 Power Supply Deck rear panel is shown below. The connectors and controls are described below
the figure.
Figure 2. KPA1500 Power Supply Deck Rear Panel.
Control: DA-15 cable with control and low voltage supplies to the RF Deck.
HV Supply: Main DC power output for the RF Deck
Ground: Connection to the station ground.
AC Power Cable: Supplied with a NEMA 6-20 molded plug. If needed, replace with a suitable 20A
connector for your installation.
Power ON Switch and Circuit Breaker: Must be in the ON position for the RF Deck power switch to
function.
Figure 3. Power Supply Front Panel.
AC ON LED. Lights green whenever the power supply is connected to AC power and the rear panel main
power switch is on (up).
HV SUPPLY LED. Lights green when the high current 50V supply is within operating tolerance. Lights red
when the output voltage is below specification. During power down, it will turn red for a few seconds. If this
LED turns red during operation, excessive current is being drawn and RF output power is reduced for
protection. Turn off power and wait until the LED goes dark before turning power back on again.
LV SUPPLY LED. Lights green when the Control System power supply is within operating tolerance.

9
Positioning the KPA1500 RF Deck and Power Supply
Provide at least 4”(10 cm) clearance behind the RF Deck fans and above the Power Supply top cover. Allow at
least 1”(2.5 cm) clearance around the top and sides of the RF Deck and around the sides of the Power Supply
for normal cooling air flow.
The supplied cables allow the Power Supply and RF Deck to be placed up to 66” (167 cm) apart. The Power
Supply can be operated remotely so there is no need for it to be within the operator’s reach. The fans operate
whenever the KPA1500 is on, so you can place the Power Supply under the operating desk or elsewhere to
minimize fan noise.
Cabling –Power Supply
Be sure the POWER ON switch is off before connecting any cables to the Power Supply or RF Deck.
An AC power cable with the popular NEMA 6-20 connector is supplied attached to the Power Supply. The
NEMA 6-20 connector is compatible with NEMA 6-20R receptacles. Replace the connector if you need a
different connection to your mains supply. Elecraft recommends a 200/240 volt AC, 20 amp circuit for proper
operation of the KPA1500.
Connect the Power Supply to the RF Deck with the supplied 66” (167 cm) cable. Plug the Anderson
PowerPole® connector into the HV Supply connector on the RF Deck rear panel (Figure 1, page 7) and the
corresponding connector on the Power Supply , Figure 2, page 8. Observe the polarity; match the colors on
the plug with the connectors.
The 75A PowerPole connectors click twice when inserted. There is no electrical connection until the
second “click.”
Connect the 15-pin connector to the Power Supply and the Control connector on the RF Deck rear panel.
Ensure the captive screws securing the connectors are tight and the connectors are fully seated.
Cabling –RF Deck
Always turn the KPA1500 off via the rear panel switch/circuit breaker on the Power
Supply before attaching or removing cables.
The KPA1500 may be used with the Elecraft K3S, K3, K2 or any HF/6 meter transmitter with a keying output
meeting the requirements shown under note 4 below. Interconnections with transceivers are shown in Figure 4,
page 11, Figure 5, page 12 and Figure 6, page 13. The driving transceiver must provide at least 50 watts of RF
for full output and the output power must be adjustable as described under Transmitting on page 16.
1. Connect your station ground to the GND terminal (see Figure 1. page 7). A good station ground is
important for safety and to minimize local radio frequency interference (RFI).
2. Attach the RF INPUT to the output of your driving transceiver or transmitter using a 50 Ω coaxial
cable with a PL-259 connector on the KPA1500 end.
3. Attach a suitable load with an SWR of less than 1.5:1 to the ANT 1 or ANT 2 connector A 50 Ω
1500 W dummy load is recommended for initial testing. Be sure to select the correct ANT connector
using the front panel ANTENNA switch before transmitting.
4. The driving transmitter must ground the KEY IN line circuit during transmit while sinking up to 5 mA.
This is compatible with virtually all amateur transmitters and no key line buffer is required. If the
transmitter Key Output is not a contact closure or equivalent, it must be at a level between +4 and +16
VDC during receive.

10
Enhanced Mode Operation with a K3 or K3S
The optional KPAK3AUX cable kit provides closer integration with a K3 or K3Sby sharing band information
between the KPA1500 and the transceiver, see Figure 5, page 12 and Figure 6, page 13. The KPAK3AUX cable
kit enables all enhanced features described under Operation, including coordinated band-switching (page 15).
The KPAK3AUX cable kit also incorporates the KEY IN line. If you need access to this line so that other
equipment can bypass the amplifier, you can install the Key Line Interrupter supplied with your KPAK3AUX
cable and use a separate key line as shown in Figure 6 on page 13.
You must use the Key Line Interrupter when using a separate key line with the
KPAK3AUX cable kit. Otherwise any external equipment inserted into the key line will not
be able to inhibit the amplifier.
Cables for Yaesu and Icom transceivers to provide closer integration with the KPA1500 are available.
See AUX and XCVR Serial Connector Interfaces on page 37.

11
Figure 4. Basic Cabling Diagram for Any Transceiver.
KPA1500
HF to 6 m
Transceiver

12
Figure 5. K3SEnhanced Cabling Using KPAK3AUX Cable, Without Interrupter.
KPA1500
K3S

13
Figure 6. K3SEnhanced Cabling Using KPAK3AUX Cable and Separate Key Line, With Interrupter.
K3S
KPA1500

14
Operation
RF Deck Front Panel Controls
Figure 7. KPA1500 RF Deck Front Panel Controls and Indicators.
The front panel controls and indicators are referred to in the following operating instructions by
the numbers shown in Figure 7. Below is a summary of the function of each control and indicator.
Switches with a legend above and below have two functions. Tap (press briefly) to
activate the function labeled above a switch. Hold to activate the function labeled
below the switch. In the text, tap functions are shown like this: MENU. An example of
a hold function is EDIT.
BAND select switches: Tap to manually select a new band see Band Switching, page 15).
MENU/ EDIT switch: Tap to enter the KPA1500 MENU system. Hold to EDIT the selected menu
parameter.
STATUS switch: Tap to display Status pages showing amplifier operating parameters (see page
Error! Bookmark not defined.).
Liquid Crystal Display (LCD).
and : Use to scroll through the Status or Menu screens.
Power Output wattmeter bargraph.
SWR bargraph. The SWR LEDs are green from 1 to 1.5. The 1.5 to 2 LEDs are yellow and the LEDs
above 2 are red.
TX LED: Lights whenever the amplifier is in operate mode (OPER) and the PA KEY signal is pulled
low (enabled).
ON pushbutton switch: Toggles the RF Deck power on or off.
ATU TUNE/ ATU MODE switch: Tap to enable the ATU Tune function. Hold to place the internal
ATU in or out of the signal path.

15
ANTENNA / PF2 switch: Tap to toggle between the ANT1 and ANT2 outputs. Hold to select user-
programmable function 2, (future feature).
MODE / PF1switch: Tap to switch between Operate (OPER) and Standby (STBY) modes. Hold to
select user-programmable function 1, (future feature).
RESET / INFO switch: Tap to reset a fault condition. Hold to display information about the last fault
on the LCD.
AUXswitch: Hold for 10 seconds to force a firmware load (see page 29).
Power On
IMPORTANT
When the KPA1500 is turned off using the front-panel switch , part of the control circuitry
remains on as long as AC mains power is applied to the Power Supply.
Keeping the control circuitry energized allows the KPA1500 to be turned on and off remotely as well as
from the front-panel switch. If you do not need to control the KPA1500 remotely and would prefer to
save the small amount of power required to power the control circuitry, either switch the Power Supply
completely off or provide an external mains power switch capable of handling 20A.
1. Ensure a suitable 50 Ωload is attached to the ANT 1 or ANT 2 connector on the rear panel. Tap
the front panel ANTENNA switch to select the antenna connector used. The associated LED will
be illuminated. A dummy load is recommended for initial tests.
2. Enable the power supply by placing the rocker switch on the power supply module in the ON (I)
position.
3. Tap the ON switch . The LCD , ANT 1 or ANT 2 and the OPER or STBY LEDs should light. By
default the KPA1500 enters Standby mode (STBY) at power on. You can change the default to start in
OPER mode using the POWER ON MODE menu item, see page 28.
If the FAULT LED lights at any time, refer to Fault Conditions, page 24.
Band Switching
Band switching may be done automatically or manually as follows:
Automatic Band Switching via Frequency Counter: The KPA1500 measures the incoming RF frequency and
automatically selects the proper band. The KEY IN input must be connected to the driving transmitter to enable
the KPA1500’s counter.
The automatic band selection via frequency counter is active whenever the KEY IN is
low (transmit mode) and the transceiver is delivering RF drive to the KPA1500. The
automatic band selection function overrides band selection made by any other means to
protect the KPA1500 from damage by wrong-band operation.
Manual Band Switching: Tap any of the front-panel BAND switches to manually switch the KPA1500
to that band. If the incorrect band is selected, the built-in frequency counter will automatically select the
proper band for the RF frequency presented to the Input.
Coordinated K3Sor K3 and KPA1500 Band Switching: When the optional AUX cable (page 10) is
connected between the KPA1500 and the K3Sor K3:
•The KPA1500 will follow the band selected on a K3Sor K3 transceiver without the need
to transmit.

16
•Tapping a BAND switch on the KPA1500 will cause the K3Sor K3 to change bands
accordingly.
The KPA1500 can automatically follow band selection from certain non-Elecraft transceivers
such as Flex Radio, Icom and Yaesu (BCD) without transmitting when the appropriate control
cable is used. This is called Enhanced Mode operation.
However, control is one-way: The KPA1500 cannot command the transceiver to change bands as
it does when connected to a K3Sor K3 with the optional AUX cable.
See AUX and XCVR Serial Connector Interface on page 37.
Antenna Selection
Tap ANTENNA to select the desired rear panel antenna connector. Either ANT 1 or ANT 2 LED illuminates to
indicate the selection.
You may designate either ANT1 or ANT2 on a per-band basis. By default, the KPA1500 will return to that
choice when returning to that band. You can configure this function with the KPA1500 Utility Configuration
panel.
You can also disable one of the antenna outputs for selected bands. See ANTENNA ENABLE and ANTENNA
PREFER entries under Menu on page 25. The KPA1500 Utility Configuration section makes it easy to configure
this function.
•If an ANT connector is disabled on any band, tapping the ANT button blinks the ANT LED, but
will not change to the disabled antenna.
When the KPA1500 is powered off, the Input port is connected directly to the ANT1 port, even if ANT1 is
disabled.
Transmitting
The POWER (W) and standing wave ratio (SWR) bargraphs are functional when the amplifier is in
standby (STBY). Twenty five watts from the driving transceiver will illuminate the first POWER LED.
You may run up to 200 watts through the KPA1500 in STANDBY.
If you attempt to drive the KPA1500 on a frequency that is more than 100 kHz
outside of an Amateur band or in the range of 26 to 28 MHz, the KPA1500
automatically switches to standby, the red FAULT LED lights and a tone is sounded
in the speaker.
1. Be sure you have an antenna or dummy load connected to the active antenna output (see Antenna
Selection above) and your driving transceiver is on a frequency inside an Amateur band.
2. In order for the KPA1500 to amplify, it must be in OPER mode and it must be keyed. The
amplifier can be keyed either by KEY IN pulled low or using the optional KPAK3AUX cable
connected to the K3/K3S.
3. If you have a 50 Ωdummy load or an antenna that you know presents a low SWR to the
KPA1500, press and hold the ATU MODE switch to put the ATU in bypass (BYP LED lights).
If you are not sure of the SWR, press and hold the ATU MODE switch to enable the ATU (IN
LED lights).
4. Tap the MODE 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.

17
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.
If your load presents a high SWR, be sure the ATU is enabled (press the ATU MODE switch to
light the IN LED), and then tap ATU TUNE to initiate a tuning cycle. Apply 25 to 50 W of
transmitter drive during this tune cycle. About 50 W of drive is required to produce the full 1500
W output from the KPA1500.
During heavy use, you may hear clicking sounds as amplifier components cool. This is
normal. It does not indicate the amplifier is being over stressed. 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 (see Menu Section starting on
page 25).
8. When driving the KPA1500 with an Elecraft K3 or K3S, 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 Using ALC, page 17).
In the K3 or K3S, program CONFIG:POWER SET to Per Band and adjust the power level for
each band. See Per-Band Power Control in your K3 or K3SOwner’s Manual for further details.
(Requires K3 firmware version 4.82 or later).
If you use the AUX cable interface between the K3 or K3Sand KPA1500 (Figure 5, page
12 or Figure 6, page 13), and you have RADIO TYPE set to K3 or K3s, the KPA1500 will
send the operate/standby status to the K3 or K3S.
This means you can set two per-band power levels with the K3 or K3S:
One to drive the KPA1500 when it is in operate mode and another for pass-through transmitting when
the KPA1500 is in standby. The K3 or K3Swill automatically return to your preset power levels as you
switch the KPA1500 between operate and standby.
Using 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 or K3S PWR SET-PER BAND function to set proper drive levels, not ALC.
The Elecraft K3 and K3SALC 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 drive to avoid ALC action in normal
operation.
If you chose to use ALC, set your transmitter power output correctly as described under Transmitting and adjust
the ALC so it does not affect output power in normal operation.
1. Drive the KPA1500 to the desired output.
2. Adjust ALC THRESH in the menu (page 25) until power just starts to drop and then set ALC THR 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.

18
Automatic Antenna Tuner (ATU)
The internal ATU may be used with the KPA1500 in either standby or operate mode. When the KPA1500 is in
standby mode, power from the driving transceiver is passed directly to the ATU. Press and hold ATU MODE to
select whether the ATU is active (IN) or bypassed (BYP). The corresponding LED above the switch will light.
The maximum bypass power through the KPA1500 INPUT connector is 200 W.
At lower amplifier outputs up to 750 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 at least 3:1. See Figure 8, page 7 below.
The ATU recalls the tune solutions based on the frequency reported by an interfaced radio or by the KPA1500
frequency counter when the KEY IN line is held low.
This tune feature works in both standby and operate modes: Frequency information from the interfaced
transceiver may be used to select an ATU setting without transmitting.
Figure 8. Antenna Tuner Matching Capability.
Manual Tune Operation
1. Tap ATU TUNE to initiate an ATU tune cycle. The ATU IN light will flash.
2. Supply 10-50 W of RF from your transceiver.
Relays in the ATU operate to switch values of inductance (L) and capacitance (C) to match the antenna
impedance to a value close to 50 Ωnon-reactive for the KPA1500 amplifier circuits or for the driving
transceiver when the KPA1500 is in standby.
The SWR LEDs indicate how close the antenna impedance is matched to the transceiver. The L and C values
switched in will provide a good match for most situations.
3. Tap ATU TUNE again within 3 seconds after tuning is completed to initiate a second, fine tuning process
with smaller changes in L and C values.
This may result in a lower SWR. You must not interrupt the RF from the transceiver for this function to
complete properly. Once the tuning operation is complete, unkey your transceiver.

19
If the SWR is 1.2 or less when a tune operation begins, the KPA1500 bypasses the matching network without
searching for a tuning solution. The ATU IN and the ATU BYP LEDs both illuminate to show the tuner is
bypassed for this frequency. When returning to the selected frequency, the internal ATU will recall the bypass
mode. The ATU IN and the ATU BYP LEDs will be illuminated again when this happens.
You can change the default bypass SWR threshold with the ATU BYPASS parameter in the Menu. Subsequent
ATU TUNE procedures will use the new threshold to determine when the internal ATU is placed into Bypass
mode.
ATU Memories
After successfully tuning, the KPA1500 stores L and C or Bypass settings and the ANT1 or ANT2 selection in
memory. They are recalled when returning to that frequency.
The entire spectrum from 1.8 through 60 MHz is divided into frequency segments and tuning information is
stored for each successfully tuned segment. These are called memory “bins.” Please see the Appendix, page 45
for a list of the center frequencies of each of the memory bins.
Re-tuning to maintain a low SWR is normally required over a narrower frequency range on the lower
frequencies, so lower frequencies have narrower segments assigned as follows:
•Below 3 MHz the segments are 10 kHz wide.
•From 3 MHz through 26 MHz the segments are 20 kHz wide.
•From 26 MHz to 38 MHz the segments are 100 kHz wide.
•From 38 MHz to 60 MHz the segments are 200 kHz wide.
When starting a tune operation for a frequency segment that has no tuning solution, the KPA1500 first tries
settings in the nearest frequency segment with tuning data.
Training the ATU Using Full Cycle Tune
To minimize the tune operation while moving from one frequency to another, you can “train”the ATU at
different points across each band. The KPA1500 memorizes the L and C settings and antenna selected.
The KPA1500 ATU will not require a full search tune operation again unless the antenna changes.
Normally you won’t need to perform a tune operation in every segment shown in the Appendix. If you
transmit in a segment where there is no tuning solution, the ATU automatically checks solutions for
adjacent segments to see if they produce an acceptable SWR.
To initiate a Full Cycle Tune, follow these steps.
1. Tap the ATU TUNE button. The ATU IN light will begin to flash to indicate it is waiting for RF from the
transceiver.
2. Apply 25 to 50 W of transmit drive. You will hear the relays searching for a match.
3. When the relays stop, the ATU IN LED stops flashing, indicating Full Cycle Tune success.
4. The resulting match is automatically stored in the appropriate memory bin. If a match cannot be found,
the red FAULT LED illuminates, NO MATCH is shown on the LCD, and no settings are stored. The
ATU can create a match for SWR as high as 10:1. If no match is found, make sure the correct frequency
band and antenna are selected.
5. You can use the KPA1500 Utility Operate panel to observe Full Cycle Tune activity and transmission
line/ antenna system SWR.
6. If you have multiple antennas on one or more bands, repeat this procedure for each antenna and
frequency combination.

20
With ATU HiSWR AUTO RETUNE set to ENABLED and an antenna SWR higher than the retune threshold,
the KPA1500 will search previous tuner settings until one is found that is as good as or better than the SWR
threshold. Once found, the setting is stored and the amplifier quickly resumes operation.
Note the ATU will not automatically begin a full-search tune. It recalls previous or adjacent-segment tuning
solutions.
Multiple Antennas and External Antenna Switches
Some stations have several antennas, all sharing the same KPA1500 antenna connector, switched externally.
The ATU memory feature is great for antenna installations with multiple antennas per band, or in situations
where the match changes with rain, ice or some other condition. The KPA1500 ATU memory allows up to 31
ATU settings for each frequency segment.
For example, you might have a dipole, a Yagi and a vertical on 20 meters, all on the ANT1 connector, selected
by an external antenna switch. The KPA1500 can store separate tuning solutions for all three antennas.
Train the tuner for each antenna, coax switch and ANT1 or ANT2 combination using the Training the ATU Using
Full Cycle Tune procedure above.
When ATU HiSWR RETUNE is enabled and you key the transmitter, the match is evaluated. If it is higher than
the ATU HiSWR RETUNE threshold (default = 1.8:1), the ATU rapidly searches saved solutions for this
frequency segment. The first match lower or equal to the ATU HiSWR RETUNE threshold is applied and the
amplifier is enabled.
The 31 ATU settings are not dedicated to either antenna connector. You may store any combination of settings
totaling 31. For example, you can set 25 ATU settings for ANT1 and 6 settings for ANT2.
Frequency Tracking with an Elecraft K3 or K3STransceiver
When used with a K3 or K3Sand interfaced using the optional KPAK3AUX cable kit, the KPA1500 may be
configured to track frequency changes without transmitting, providing virtually instantaneous amplifier and
ATU setting updates as you tune the receiver across the band.
To use frequency tracking:
1. Connect the KPA1500 and K3 or K3Susing the AUX interface cable as shown in Figure 5, page 12 or
Figure 6, page 13.
2. Ensure the K3 or K3Sis equipped with firmware revision 4.82 or later. See Firmware Upgrades in your
K3 or K3SOwner’s Manual for more details.
3. Enable the frequency tracking function in the K3 or K3S:
a. Select CONFIG: KAT3 and then tap the 1 switch to toggle between KAT500N (no KPA1500)
and KAT500Y (KPA1500 connected and frequency tracking enabled).
This is the same procedure that enables frequency tracking with the KAT500 tuner.