Elecraft KXAT1 User Manual
ELECRAFT KXAT1 AUTOMATIC ANTENNA TUNER
Assembly and Operating Instructions
Revision B, July 27, 2011. Copyright © 2011, Elecraft; All Rights Reserved
Introduction
The KXAT1 internal automatic antenna tuner (ATU) allows random-length, end-fed wire antennas to be
connected directly to the Elecraft KX1 transceiver and used on one or more bands. It can be also be used
with most coax-fed antennas, or with balanced feedlines via a balun. Like our KAT1, KAT2, and KAT100
auto-tuners, the KXAT1 functions on receive as well as transmit. This provides an increase in receive
sensitivity and improves rejection of out-of-band signals.
The KXAT1 uses latching relays to reduce current drain to nearly zero except when tuning. The se relays
select appropriate combinations of inductance and capacitance, as well as either a capacitor-in or capacitorout L-network configuration. Tune-up is controlled by the KXAT1's microprocessor, which also supplies
SWR and power information to be displayed on the KX1's 3-digit LED display. Once a match has been
found, matching parameters are saved so that the settings can be recalled immediately on any band change.
ATU parameters (L, C, SWR, etc.) can be viewed using the KX1’s ATU menu entry. Additional settings
are provided to perform component-level troubleshooting of all relays and L-network components.
In addition to being one of the world’s smallest automatic antenna tuners, the KXAT1 is very easy to build
and install. The KXAT1 module plugs directly into the KX1’s main board with no additional wiring. Gold
plated connectors and redundant connector pins are used to provide excellent reliability for field operation.
Specifications
L/C Ranges L (inductance): 0-4.5 µH in 7 steps; C (capacitance): 0-140 pF in 7 steps
Network Type L-network (series L, shunt C); C switchable to transceiver or antenna side
Tuning time 1 to 3 seconds typical for initial tune-up; < 1/2 sec. to recall per-band settings
SWR Display 1.0:1 to 9.9:1
Current Drain Approx. 10-30 mA during TUNE; < 1 mA at all other times
Size 4.8" (L) x 1.0" (D) x 0.5" (H) (12.2 x 2.5 x 1.3 cm)
Weight 1 oz.
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Ca
ution: 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.
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Parts Inventory
The table below lists all parts in the kit. The KX1 Owner's manual has photographs of similar parts.
Ref. Description Qty Part No.
C1 Capacitor, 20 or 22 pF ("20," "22," "200," or "220") 1 E530017
C2 Capacitor, 39 pF ("39" or "390") 1 E530036
C3 Capacitor, 82 pF ("82" or "820") 1 E530038
C4-C8,C11 Capacitor, .01 µF ("103") 6 E530019
C10 Capacitor, 100 pF, 200 V, NPO disc ("101") 1 E530034
C9 Capacitor, 1-40 pF trimmer 1 E540002
D1,D2 Diode, 1N5711 2 E560004
K1-K7 Relay, DPDT 7 E640010
L1,2,3 T37-2 toroid core, red, 0.37" diameter
(L1=0.64 µH,12T; L2=1.3 µH, 17T; L3 = 2.6 µH, 25 T)
P1 Connector, 3 pin male, 0.1" spcg 1 E620071
P2 Connector, 2 pin male, 0.1" spcg 1 E620072
P3 Connector, 5 pin male, 0.1" spcg 1 E620073
R1,R2 Potentiometer, 100 k trimmer, low-profile 2 E520012
R3 Resistor, 200 ohms, 1/4-W, 5% (red-black-brown) 1 E500020
R4 Resistor, 3.3 k, 1/4-W, 5% (orange-orange-red) 1 E500017
RFC1 Miniature RF choke, 15 µH (brown-green-black) 1 E690012
T1 Transfor mer on FT37-43 core, 10 turns bifilar (see text) 1 E680003
U1 MCU, KXAT1, PIC16C716 1 E610016
Z1 Ceramic resonator, 4.0MHz +/- 0.2% 1 E660001
MISC KXAT1 PC board (part of KX1 PC board set) 1 E100175
MISC Enamel wire, #26 red 5 ft. E760002
MISC Enamel wire, #26 green 2 ft. E760004
MISC Solid, insulated hookup wire, green 1 ft. E760008
MISC Socket for U1, 18 pins 1 E620031
MISC Foot, self-adhesive (spacer between ATU/bottom cover) 1 E700024
3 E680006
Parts Placement Drawings
Parts placement drawings for both sides of the KXAT1 PC board can be found in Appendix F of the KX1
manual.
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Assembly
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A fine-point, temperature-controlled soldering iron (700-800 degrees F) is required to assemble
this kit. 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 shor ts.
and microcontroller U1). Double-check all values before soldering, since removing parts from double-sided
PC boards can be difficult.
bend the relay leads.
soldered pin while pressing down on the relay. Once all relays are properly seated, solder all pins.
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All parts are installed on the top side of the board except as noted (the side with the relays, toroids,
Place relays at locations K1-K7 as shown by their component outlines. Do not solder yet. Do not
Using a flat object to hold K1-K7 in place, flip the board over. Solder just one inner pin on each relay.
Inspect the relays closely to make sure that they’re seated flat against the PC board. If not, re-heat the
Trim the relay leads as short as possible to provide clearance for folded capacitors in a later step.
Install the IC socket at U1. Align the socket's notched end with the notch in the component outline.
On the bottom side, install R3 (200 ohms, red-black-brown) and R4 (3.3 k, orange-orange-red).
Install D1 and D2, with the banded end of each diode oriented as shown on the board.
Install ceramic resonator Z1, which looks like a capacitor with three leads. It can be installed in either
of two orientations. Keep soldering time to 2-3 seconds per lead to avoid overheating the part, which can
alter its frequency. Trim the leads after soldering.
Install trimmers R1 and R2 on the bottom side. Make sure they are seated flat against the PC board.
Install RF choke RFC1 (brown-green-black). The leads are fragile—handle carefully.
Install the trimmer capacitor, C9, on the bottom side. The flat side should be oriented as shown by the
component outline, and the trimmer must be seated flat against the board.
Install the capacitors listed below on the bottom side of the board, but don't solder them yet. Leave the
leads about 0.1" long so the capacitors can be folded down in the next step. All possible value markings are
shown in parentheses.
__ C1, 20 or 22 pF (20, 22, 200, or 220) __ C2, 39 pF (39 or 390)
__C3, 82 pF (82 or 820) __ C10, 100 pF (101)
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Fold down C1, C2, and C3 at about a 45-degree angle, but not so far that they contact the nearby relay
pins. C1 should be folded toward K1, C2 toward K4, and C3 toward K2.
Solder C1-C3 and C10 from the bottom side to avoid damaging the relays. Trim the leads on the top.
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In the following step, the installed height of the capacitors must be no more than 5/16" (7.5 mm).
The leads may be pre-formed so that the capacitors sit a small distance above the board. As long as the
installed height is below the limit specified, there's no need to straighten the leads.
should be seated as far down onto the board as possible (see above).
adjust the windings to precisely match the inductances shown on the schematic.
inductor, pass the long end of the wire through the core exactly 12 times. Each pass through the core
counts as one turn. The finished winding should look like the illu stration below. Exact turns spacing is not
critical.
Install the .01-µF capacitors ("103") on the top side of the board (C6, C4, C5, C7, C8, C11). They
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In the following steps, inductors L1 through L3 will be wound and installed. There is no need to
Inductor L1 is wound on a T37-2 core (red) us ing 8" (20 cm) of #26 red enamel wire. To wind the
Spread out the turns of L1 so they occupy about 80-90% of the core’s circumference.
Cut L1's leads to about 1/2" (12 mm) long. Completely remove the enamel insulation from the leads
to within 1/8” (3 mm) of the core. The enamel wire provided can be heat-stripped using a small amount of
solder on the tip of your iron. Stripping using this method takes 4-6 seconds.
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