Elecraft KAT2 User Manual
ELECRAFT KAT2 AUTOMATIC ANTENNA TUNER
Assembly and Operating Instructions
Revision F, August 3, 2012. Copyright © 2012, Elecraft; All Rights Reserved
Introduction
The KAT2 internal automatic antenna tuner (ATU) allows nearly any antenna to be connected directly to
the K2 and used on most if not all bands. The L-network configuration provides a wide impedancematching range, and can be used directly with coax-fed or end-fed wire antennas, or with balanced
feedlines via a balun. Unlike some internal auto-tuners, the KAT2 functions on receive as well as transmit.
This provides an increase in receive sensitivity and improves rejection of out-of-band signals.
The KAT2 uses latching relays to reduce current drain to nearly zero except when actually tuning. These
relays select appropriate combinations of inductance and capacitance, as well as either a capacitor-in or
capacitor-out L-network configuration. Tune-up is controlled by the KAT2's microprocessor, which also
supplies SWR or power information to be displayed on the K2's LCD. Once a match has been found, the L,
C, and other matching network data are stored in EEPROM so that the settings can be recalled immediately
on any band change. ATU parameters (L, C, SWR, etc.) can also be viewed using the menu.
Two antenna jacks are provided on the ATU, with the matching network data for both antennas stored on a
per-band basis. Once an initial match has been obtained for both antennas on a particular band, the operator
can tap the
fraction of a second to switch, it becomes practical to quickly try both antennas anytime the distant station
is weak, an advantage during contest operation.
Specifications
L - C Ranges L: approx. 0-20 µH in 256 steps; C: approx. 0-2400 pF in 256 steps
Network Type L-network (series L, shunt C); C switchable to transceiver or antenna side
SWR Range Matched Up to 10:1 typ. (varies with band; smaller range on lowest/highest bands)
Tuning time 1 to 5 seconds typical for initial tune-up; < 1/2 sec. to recall stored settings
SWR Display 1.0:1 to 9.9:1
Power Display 0-20 watts (approx.); forward and reflected power shown in 0.1-w increments
Current Drain Approx. 10-30 mA during TUNE; < 5 mA at all other times
Size 4.2" (L) x 1.6" (D) x 1.5" (H) (10.7 x 4.0 x 3.8 cm)
ANT 1/ 2 button on the front panel to switch between them. Since the relays take only a small
Elecraft • www.elecraft.com • 831-763-4211
Parts Inventory
The table below lists all parts in the kit. If you have trouble identifying any of these items, consult the
K2 Owner's manual, which has photographs of similar parts.
Components on KAT2 Module
Ref. Description Qty.
C1 Capacitor, 10 pF, 500 V NPO disc 1
C2 Capacitor, 22 pF, 500 V NPO disc 1
C3 Capacitor, 39 pF, 500 V NPO disc 1
C4 Capacitor, 82 pF, 500 V NPO disc 1
C5 Capacitor, 150 pF, 500 V NPO disc 1
C6 Capacitor, 300 pF, 500 V silver mica, CDE FD301J03 1
C7 Capacitor, 620 pF, 500 V silver mica, CDE FD621J03 1
C8 Capacitor, 1200 pF, 500 V silver mica, CDE FD122J03 1
C20-27, C31-38,
C42, C45-47,
C50-C53, C57, C60
C58, C59 Capacitor, 0.1 µF, 25 V ("104") 2
C54 Capacitor, 100 pF, 200 V, NPO disc ("101") 1
C55 Ceramic trimmer, 5-30 pF 1
D1, D2 Diode, 1N5711 2
E1 Screw terminal, PC-mount, Keystone #8190 1
J1, J2 BNC jack, PC-mount 2
J4, J5 Conn., 16-pin female, .1" spcg., gold, Samtec ESW-116-23-G-S 2
J3 Not used (connections are soldered; see text) 0
K1-K18 DPDT latching relay 18
L1-L7 Toroidal inductor, T50-2 core (RED); see text 7
L8 Toroidal inductor, T50-1 core (BLUE); see text 1
P4, P5 Conn., 16-pin male, .1", gold, Samtec MTSW-116-22-G-S-420 2
R1, R2 Trimmer potentiometer, 100K 2
R6 Resistor, 47 Ω, 5%, 1/4-watt (yellow-violet-black) 1
R3 Resistor, 200 Ω, 5%, 1/4-watt (red-black-brown) 1
R5 Resistor, 470 Ω, 5%, 1/4-watt (yellow-violet-brown) 1
R4 Resistor, 3.3 K, 5%, 1/4-watt (orange-orange-red) 1
T1 Toroidal transformer, FT37-43 core (gray); see text 1
U1 IC, Microcontroller, 16C77 1
U2 IC, EEPROM, 25LC320 1
U3 IC, 6-volt regulator, 78L06 1
U4 IC, Op-amp, LM358 1
Z1 Ceramic resonator w/internal capacitors, 4.0 MHz 1
Capacitor, .001 µF, 25 V("102") Note: Two of these capacitors
may be physically smaller than the other capacitors even t
though they have value. If so, reserve those capacitors for use at
C45 and C60.
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2
Hardware and Miscellaneous
Ref. Description Qty.
HDWR Rubber insulator, 0.5” dia. (round, black), p/n 6135-017-BLK 6
HDWR Socket for U1, 40 pins, open frame 1
J7 Conn., 2-pin housing, 0.156", Digikey WM2111 1
HDWR Female crimp pin for J7, gold, Digikey WM2305 2
J8 Conn., 10-pin dual-row 0.1" housing, Digikey WM2522 1
HDWR Female crimp pin for J8, tin, Digikey WM2556 12
RF-P6 Conn., 2p male, 0.156”, gold, Digikey WM5224 1
HDWR #4 split lock washer 6
HDWR 4-40 x 1/4” ZN ST Phillips machine screw 4
HDWR Standoff, 3/16” dia. x 13/16”, 4-40 thd, RAF #1642-440-A 2
HDWR Binding post, black, 6-32 threaded, Keystone #7007 1
HDWR BNC connector cap, black plastic, 3/8" dia. x 1/2” long 1
MISC Enamel wire, #26 Thermaleze, GREEN 2 ft.
MISC Enamel wire, #26 Thermaleze, RED 10 ft.
MISC Insulated hookup wire, #24, solid 1 ft.
MISC Cable, 4-conductor + shield, Digikey W404-X-ND 2 ft.
MISC Coaxial cable, RG-174 1 ft.
MISC KAT2 Control board 1
MISC KAT2 L-C board 1
MISC Cable ties, 3” 4
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Caution: Some components in this kit can be damaged by static discharge. Before
handling any transistors or integrated circuits, always put on an anti-static wrist strap or touch any
grounded, unpainted metal surface.
K2 Firmware Requirements
To use the KAT2 antenna tuner, you'll need K2 main processor firmware revision 1.04 or later. (The main
processor is U6 on the K2's control board.) Revision 1.05 or later is recommended, since it provides
additional ATU operating features (see Using the ATU). The latest K2 firmware revision can be ordered as
an upgrade (refer to our web page for details).
To check your main processor firmware revision, hold any button when powering up the K2. The number
shown at the left end of the display is the revision number. If you have an older version, contact Elecraft.
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ATU Control Board Assembly
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A fine-point, temperature-controlled soldering iron (700-800 degrees F) is required
to assemble this kit, due to the high density of the PC board layout. A high-wattage iron
or one with a wide tip may damage components, pads, or traces. Use a minimum amount
of solder to avoid ground shorts.
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To avoid difficulties in soldering adjacent components, install components only in
the order described below. Double-check all values before soldering, since removing
parts from double-sided PC boards can be difficult.
There are two identically-sized PC boards in the ATU kit. Locate the ATU Control board, which is
labeled "ATU CTRL" on the bottom. Set the L-C board aside for now.
Referring to the parts list (page 2), install R3, R4, and R5. Note: R6 (47 Ω) and R5 (470 Ω) have very
similar color codes. Be sure to install the 470-Ω resistor at R5 (yellow-violet-brown).
Install D1 and D2 (1N5711), observing proper orientation of the banded end of each diode.
Install the capacitors listed below. The capacitor markings are shown (e.g., "102" = .001 µF).
IMPORTANT: If two of the capacitors are physically smaller than the others even though they
have the same value, use them at C60 and C45.
__ C57 (102) __ C58 (104) __ C60 (102) __ C59 (104) __ C53 (102)
__ C52 (102) __ C45 (102) __ C46 (102) __ C47 (102) __ C54 (101)
__ C50 (102) __ C51 (102)
Ceramic resonator Z1 looks like a capacitor with three leads. It is not polarized, so it can be installed
in either orientation. Install Z1 near U1.
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The IC socket to be installed in the next step is an open-frame type. A smaller IC (U4) will be
installed within an opening in this socket. Do not substitute any other socket type.
Install the 40-pin IC socket for U1, with the notched end of the socket oriented towards pin 1.
Install voltage regulator U3, which has a 3-lead package like a transistor.
(Note: Touch a grounded metal surface before handling the following components.) Install the two 8-
pin ICs, U2 (25LC320) and U4 (LM358), with the notched end of each IC oriented as indicated by its
component outline. Note that U4 fits within the opening in U1's 40-pin IC socket.
The two latching relays, K17 and K18, must be installed with their white-striped ends oriented as
indicated on the PC board. Do not bend the relay leads. Solder two diagonal corner pins on each relay
first, then re-heat the connections and press the relays flat on the board before soldering the remaining pins.
4
Install BNC jacks J1 and J2. These connectors must be seated flat on the PC board and aligned
with the board's edge to allow for proper installation in the top cover. Solder one of the alignment pins
first, then re-heat the connection while pressing down on the jack. Once you're sure the connector is seated
correctly, solder the other pins.
Install screw terminal E1. (If E1 was supplied with a screw, remove it. The screw will not be used.)
Like J1 and J2, this component's alignment is critical. Use the same mounting technique.
Transformer T1 is wound on a dark gray toroidal core (ferrite, 3/8" [9 mm] diameter). Cut two 10"
(25 cm) lengths of #26 enamel wire, one red and one green. Twist the two wires together loosely, crossing
over each other about 2 to 3 times per inch (once per cm). Then wind the twisted wires onto the core as
shown below, using 10 turns. Each pass through the core counts as one turn.
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T1 must be wound exactly as shown, with leads 1 and 3 emerging from the back side of
the core and leads 2 and 4 from the front side.
4 (GRN)
2 (RED)
3 (GRN)
1 (RED)
Trim the leads of T1 to about 1/2" (12 mm) long. Completely remove the insulation from T1's leads
up to the edge of the core, using a solder pot or hot soldering iron tip. Do not attempt to burn off the
insulation using a match or lighter, as the flame may fuse the pairs of wire together, causing them to
become shorted. Another way to remove the insulation is to use fine sand paper.
Tin T1's leads with solder. If the leads do not tin easily, the insulation may not be fully removed.
Using an ohmmeter, measure between the red and green wires to make sure that they're not shorted.
Install T1 as indicated by its PC board outline near the right end of the board. Insert the leads into the
numbered holes as shown by the drawing of T1, above. Pull the leads taut on the bottom of the board.
Before soldering, use a magnifying glass to make sure that the entire portion of exposed lead is properly
tinned.
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Cut a 1-1/8" (2.9 cm) length of insulated, solid-conductor hookup wire. Remove exactly 1/4" (6 mm)
of insulation from each end. This jumper will form the 1-turn link winding of T1.
Insert one end of this wire through the center of T1 and into the pad labeled 5. Bend the wire down to
the right and insert the other end into the pad labeled 6. Pull the leads of the wire taut on the bottom of the
board, then solder.
Trimmer potentiometers R1 and R2 mount on the bottom of the ATU Control board. Press them down
as far as possible before soldering.
Set both trimmers fully clockwise as viewed from the bottom of the board.
Install trimmer capacitor C55 on the bottom of the board.
Note: The microprocessor and connectors J4 and J5 will be installed later.
ATU L-C Board Assembly
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All L-C Board components should be mounted in the order given here. Any other assembly order
may make soldering or mechanical alignment difficult. Also, the components must be mounted as close as
possible to the board using short leads. Follow all instructions carefully.
Install .001 µF ("102") capacitors C20-C27 on the top of the L-C Board (the side with L1-L8 and C1-
C8). There should be no excess lead length above the board.
Install .001 µF capacitors C31-C35, C37-C38, and C42. Do not install C36 at this time.
Trim all capacitor leads on the bottom of the board to the shortest length possible.
Install relays K1-K16 on the bottom of the L-C Board as follows. First, position all 16 relays on the
board, without soldering. Align the white stripe on each relay with the striped end of its component outline.
(Note that the relays are in two rows that face in opposite directions.) Next, hold the relays in place using a
flat object such as a hard-cover book. Flip the PC board and flat object over together, then examine the
relays to make sure they are all still flat against the board.
Solder two diagonally-opposite corner pins on each relay. Look at all relays once more to verify
that they are not spaced any distance away from the board. Then solder all the remaining pins.
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The following step is very important. Normally, relay pins need not be trimmed. But in this case
components will be mounted above the pins, so trimming them is necessary to prevent shorts. Trimming
must be done after soldering to prevent mechanical damage to the relay pins.
Trim all relays leads to the shortest possible length. Use flush-cut type diagonal cutters if available.
Note: Wear eye protection and aim the leads away from you when cutting. Trimming the leads over a waste
basket will eliminate cleanup.
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Refer to the drawing below during the following steps. This left end view shows how the L-C and
Control boards will appear when connected together. Relays K1 and K2 can be seen on the bottom of the
L-C board, along with 16-pin male connector P4. On the control board, J2 (BNC), R5, and R6 are visible,
as well as 16-pin female connector J4. The 13/16" standoffs are omitted for clarity.
L-C
P4
J4
Control
Locate the two 16-pin male connectors, P4 and P5. These connectors must be installed on the bottom
of the L-C board, between the two rows of relays (see above). Do not solder all pins of P4 and P5 at this
time. Instead, position the connectors, then solder only pins 1 and 16 on each connector. Make sure the
connectors are perpendicular to the board.
Install the two 16-pin female connectors, J4 and J5, on the top of the Control board as shown above.
Solder only pins 1 and 16 of each connector. Make sure the connectors are perpendicular to the board.
Plug the L-C board into the Control board as shown, mating P4 with J4 and P5 with J5. Be very
careful to avoid bending any pins on P4 and P5. Once the boards are properly mated, secure the L–C board
to the Control board standoffs temporarily using two 4-40 screws.
Press the two boards tightly together at both ends and in the middle. Once the 16-pin connectors
appear to be perpendicular to the boards and seated completely flat, solder all pins of P4, P5, J4, and J5.
Remove the screws holding the L-C board to the two standoffs. Then unplug the L-C board from the
Control board using the following method: Using a small screwdriver or Allen wrench, pry P4 upwards a
small amount, then pry P5 upwards a small amount, repeating this until the L-C board can be easily
unplugged. Do not pull the boards apart directly, as this may bend pins on P4 and P5.
Some pins on the bottom of the Control board must be trimmed to prevent shorting to the
K160RX option module. Trim the pins of the following components: E1, J5, C45, C46, C47, and J1
(signal pins only, not the large ground posts).
Carefully examine the entire ATU Control board for solder splashes or unsoldered pins (both sides).
Install C36 on the L-C board (.001 µF, "102").
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Refer to the drawing below during the following steps. The top view shows the approximate location of
the windings and pads for each inductor. The side view shows how capacitors C1-C8 and inductors L1-L8
must be mounted, including round rubber insulators for L3-L8.
BLUE CORE
L1
C5
C6 C8
L2 L7
Install C4 (82 pF) as shown above. Trim the leads to about 1/8" (3 mm) long, and bend them down at
right angles to the capacitor body. (Adjust the lead spacing to match the pads.) Insert the leads into the C4
pads just far enough to hold the capacitor in place. Do not insert the leads all the way through the board.
They could puncture the relay on the opposite side during soldering, causing a short.
Solder C4. Adjust the body of the capacitor so that it is parallel to the board and not overlapping the
location for C2 or L6. Also make sure it doesn’t touch any relay pins or pads.
Install C3 (39 pF) in the same manner as C4.
L4
C3C1
C2L3
C4
L5
C7
L8
L6
Install C1 (10 pF) and C2 (22 pF) as shown in the drawing, with the bodies of the capacitors tilted
over C3 and C4, respectively, at about a 45-degree angle.
Install C5 (150 pF), C6 (300), C7 (620) and C8 (1200). The bodies of these capacitors should be
parallel to the board and not interfering with adjacent components.
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In the following steps, L1 through L8 will be wound and installed. There is no need to adjust the
windings to precisely match the inductances shown on the schematic. The inductances need only be
approximate, since for any given antenna match only a subset of the inductors will be used.
Cut a 2-1/8" (5.5 cm) length of insulated hookup wire. Remove 1/8" (3 mm) of insulation from each
end. Wind this wire onto a red toroid core as shown in the top view of the L-C board (2 turns).
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