ELECRAFT KFL1-4 User manual

Elecraft • www.elecraft.com • 831-763-4211
ELECRAFT KFL1-4 FOUR-BAND FILTER BOARD
Assembly and Operating Instructions
Revision B, December 7, 2011. Copyright © 2011, Elecraft; All Rights Reserved
Important Manual Note
Assembly, alignment, and other information about the 4-band Filter board is covered in this manual, not in
the K1 Owner's Manual. Wherever the owner's manual mentions the 2-band module, you'll need to refer to
the applicable sections of this manual instead.
Please read the K1 Owner's Manual Errata Sheet now and make all corrections listed. The errata
sheet provides notations that will tell you when to refer to the KFL1-4 manual. Also, if you're just starting
to build your K1, read the first three chapters of the owner's manual before assembling this board.
Introduction
The KFL1-4 Filter board provides four of the most popular HF QRP bands on a single plug-in module: 40,
30, 20, and either 17 or 15 meters. The KFL1-4 is the same size as the 2-band K1 filter board (KFL1), and
can simply be plugged into the K1 transceiver with no other required changes.
The 4-band filter board is fully compatible with the KBT1 battery option and the KAT1 automatic antenna
tuner (ATU). With most antennas, the ATU will find a good match on all four bands.
The KFL1-4 covers the frequency ranges listed below. These ranges are approximate, and depend on which
VFO range the builder chooses during assembly (80 or 150 kHz). The builder must also select either 17 m
or 15 m band coverage. These topics are covered later in the manual.
Band 80 kHz VFO Range 150 kHz VFO Range
40 m 7.0-7.08 7.0-7.15
30 m 10.1-10.18 10.0-10.15
20 m 14.0-14.08 14.0-14.15
17 m 18.05-18.13 18.05-18.20
15 m 21.0-21.08 21.0-21.15
iCaution: Some parts in this kit can be damaged by static discharge or by dropping them
onto a hard surface. Before handling the integrated circuit (U1), put on an anti-static wrist strap, or
touch a grounded, unpainted metal surface. When handling crystals and toroid cores, be careful not
to drop them onto a hard surface.

2
Parts Inventory
The table below lists all parts in four-band filter board kit. The photographs in Appendix A of the K1
owner's manual may be helpful in identifying components. If anything is missing, contact Elecraft.
Note: Some capacitors use lettered reference designators, e.g. "CA". This is explained later in the manual.
Ref. Descri
p
tion Part No.
Q
t
y
C9 Capacitor, 2 pF ("2") or 2.2 pF ("2r2") E530047 1
CJ Capacitor, 2.7 pF ("2r7") or 3.3 pF ("3r3") E530065 1
C10, CK Capacitor, 4.7 pF ("4r7") or 5 pF ("5") E530048 2
C22, C26 Capacitor, 27 pF ("27" or "270") E530060 2
C29, C33 Capacitor, 56 pF ("56" or "560") E530015 2
C11-C14 Capacitor, 68 pF ("68" or "680") E530007 4
C24 Capacitor, 82 pF ("82" or "820") E530038 1
C21, C27, CN, CP Capacitor, 100 pF ("101") E530034 4
CL, CM Capacitor, 120 pF ("121") E530041 2
C31 Capacitor, 150 pF ("151") E530049 1
C23, C25 Capacitor, 180 pF ("181") E530008 2
C28, C34 Capacitor, 330 pF ("331") E530043 2
C30, C32 Capacitor, 560 pF ("561") E530052 2
C19, C35-C45 Capacitor, .001 µF ("102"), 0.1" lead spacing E530074 12
C15, C16, C17 Capacitor, .047 µF ("473") E530025 3
C46 Capacitor, 0.1 µF ("104"), 0.1" lead spacing E530020 1
C1-C8,CA-CH Trimmer capacitor, 1-40 pF E540002 16
J1 Conn., 3-pin female E620009 1
J2 Conn., 10-pin female (dual row, 5 pins per row) E620045 1
K1-K8 Miniature DPDT relay E640010 8
L1-L6, T1-T4 Toroidal inductor, T37-6 core (see text) E690013 10
P1, P2, P3 Conn., 8-pin male E620004 3
R1 Resistor, 100 ohms, 1/4 watt, 5% (brown-black-brown) E500010 1
RFC1 RF Choke, 100 µH (brown-black-brown; larger than R1) E690004 1
U1 IC, programmed microcontroller, PIC16C621A-04/P E610010 1
X1A Crystal, 29.000 MHz (for 21.0 MHz band) E660005 1
X1B Crystal, 26.050 MHz (for 18.0 MHz band) E660012 1
X2 Crystal, 22.000 MHz (for 14.0 MHz band) E660004 1
X3A Crystal, 18.100 MHz (for 10.1 MHz band) E660010 1
X3B Crystal, 18.000 MHz (for 10.0 MHz band) E660007 1
X4 Crystal, 15.000 MHz (for 7.0 MHz band) E660008 1
Z1 Ceramic resonator, 4 MHz E660001 1
Misc. Socket for U1 (18 pins) E620031 1
Misc. PC board, KFL1-4 E100129 1
Misc. Wire, #26 enamel, red E760002 12 ft
Misc. Wire, #26 enamel, green E760004 4 ft.

3
Firmware Requirements
The KFL1-4 four-band Filter board does not require upgraded K1 firmware to operate. The main
microcontroller in the K1 (U1 on the Front Panel board) will recognize whether a 2- or 4-band filter board
is present at power-on.
The KAT1 (automatic antenna tuner option) firmware will also work with the 4-band module.
Filter Board Assembly
iA fine-point, temperature-controlled soldering iron or soldering station (700-800 degrees F)
is strongly recommended to assemble the KFL1-4 PC board. If you don't have a soldering station, check
our web site (Builder Resources page) for suggested models. A higher-wattage iron or one with a wide tip
may damage components, pads, or traces.
Locate the KFL1-4 PC board and identify the top and bottom sides. The side of the board with the
label "KFL1-4" is the top.
Orient the board so that the top side is facing up. The large notch in the board should be to the lower
right.
Locate the position of resistor R1, along the front edge of the board (top side). The label "R1" appears
to the right of the resistor's outline.
Install a 100-ohm resistor (brown-black-brown) at R1. (Don't confuse it with RF choke RFC1, which
is larger.) Make sure it is seated flat on the board, then bend the leads outward slightly to hold it in place.
Solder R1 from the bottom side of the board. Then trim the leads as close as possible to the solder
joints.
Note: Many builders prefer to trim leads before soldering. Either order will work.

4
iThe approximate locations of the 16 trimmer capacitors on the Filter board are shown in Figure 1.
Relays K3-K6 are shown for reference. Note that each trimmer's body has a narrow end, and that they
are not all oriented in the same direction. The trimmers must be oriented as shown to keep their rotor
terminals at ground potential. This will allow them to be aligned with a metallic tool.
Figure 1
Install trimmer capacitors C1-C8 and CA-CH with their narrow ends oriented as indicated above
(toward the flat side of the outline on the pc board). Each trimmer must be gently pressed down as far as it
will go, but be careful not to bend the leads.
Solder all of the trimmer capacitors. Use just enough heat and solder to produce a clean, shiny solder
joint (and fill the hole). It should take no more than 2-3 seconds to solder each lead. Do not trim the leads.
Place relays K1-K8 at their indicated locations. DO NOT bend the relay leads to hold the relays on
the board, as this can cause mechanical stress. Note that the relays can only be installed one way due to
a gap between pins.
Carefully flip the board over, using a hardcover book to hold the relays in place. Make sure none of
the relays have fallen out, and that their leads are fully inserted into their PC board holes.
Solder just two pins (at opposite corners) on each relay, using a minimum amount of solder. Limit
soldering time to 2 or 3 seconds per pin to avoid damaging the relays.
Look at the relays from the top side of the board. If any of them are not fully seated onto the PC board,
re-heat the pins one at a time and gently press the relays down.
Solder all remaining relay pins. Do not trim the leads.

5
iWhen handling capacitors in the following steps, do not pull on the leads or bend them
excessively, since they can be quite fragile. In the case of capacitors with pre-formed leads, there is no
need to remove any bends. The short, pre-formed portion of the leads can remain exposed (above the
board) after installation.
Sort all of the capacitors, arranging them by value. This will make it easier to locate the correct
capacitor values during assembly. (Some small capacitor values may be labeled in more than one way. This
is explained page 9 of the K1 Owner's Manual. Also refer to the parts list, which shows alternate labeling.)
Install the capacitors listed below, but do not solder yet. Complete one row of the list before moving to
the next (the arrows in the list serve as a reminder). Start with capacitor C13 (68 pF), which is located near
the left end of the PC board, then go on to C11, C9, etc.
__ C13, 68 ("68") __ C11, 68 ("68") __ C9, 2 pF ("2") or 2.2 pF (2r2)
__ C12, 68 ("68") __ C14, 68 ("68")
Using the list above, double-check each capacitor's value. This step should not be skipped, since it
may be difficult to remove capacitors after they are soldered in place.
Trim and solder the leads of all capacitors installed so far.
C10 may be 4.7 pF ("4r7"), or 5 pF ("5"). To locate the position for C10, first find relays K2 and K3.
C10 is directly between the two. Install C10, then trim and solder.
Install the capacitors listed below, which are separated into three groups. After installing all the
capacitors in a group, double-check the values, then trim and solder the leads.
__ CL, 120 ("121") __ CM, 120 ("121") __ CN, 100 ("101")
__ CP, 100 ("101") __ CJ, See note 1 below __ CK, See note 2 below
__ C15, .047 ("473") __ C16, .047 ("473") __ C17, .047 ("473")
__ C43, .001 ("102") __ C44, .001 ("102") __ C45, .001 ("102")
__ C21, 100 ("101") __ C22, 27 ("27") __ C23, 180 ("181")
__ C24, 82 ("82") __ C25, 180 ("181") __ C26, 27 ("27")
__ C27, 100 ("101")
__ C28, 330 ("331") __ C29, 56 ("56") __ C30, 560 ("561")
__ C31, 150 ("151") __ C32, 560 ("561") __ C33, 56 ("56")
__ C34, 330 ("331")
Notes:
1- CJ may be 2.7 pF ("2r7") or 3.3 pF ("3r3").
2 - CK may be 4.7 pF ("4r7") or 5 pF ("5").

6
Install the capacitors listed below, which are all located on the bottom side of the board. Do not solder
yet.
__ C46, 0.1 ("104") __ C42, .001 ("102") __ C41, .001 ("102")
__ C40, .001 ("102") __ C39, .001 ("102") __ C38, .001 ("102")
__ C37, .001 ("102") __ C19, .001 ("102") __ C36, .001 ("102")
__ C35, .001 ("102")
Bend and trim the leads of the capacitors just installed. When soldering them, be very careful not to
touch any of the top-mounted components with the soldering iron (especially relays). If necessary, bend the
top-mounted capacitors slightly to keep them out of the way.
Install a 100-µH RF choke (brown-black-brown) at RFC1, on the top side of the board. Form the leads
of RFC1 using long-nose pliers to fit between the indicated pads. Trim the leads and solder.
Install an 18-pin IC socket at U1, with the notched end of the socket toward the notched end of the
IC's PC board outline. Bend two leads of the socket slightly to hold it in place while soldering. (U1 itself
will be installed in a later step).
Install the ceramic resonator, Z1. (Z1 looks like a capacitor with three leads, and can be oriented in
either direction.) Limit soldering time to 2 or 3 seconds on each pin to avoid altering Z1's oscillation
frequency. Trim Z1's leads after soldering.
iBefore crystals X1-X4 can be installed, you’ll need to choose whether to set up your K1 for 80-
kHz or 150-kHz VFO coverage1. The 80 kHz range covers the most-used portion of each CW band, and
will provide slightly smoother tuning. Refer to the Frequency Ranges table on page 1 of this manual for
details.
Indicate your VFO range selection here for reference: ___ 80 kHz ___ 150 kHz
Also note your selected VFO range on page 12 of the owner's manual (right column).
Two different crystals, X3A and X3B, are supplied for the 30 meter band. Identify the appropriate
crystal using the table below, and store the unneeded crystal. (X3 will be installed in a later step.)
VFO Range Lower Band Edge Crystal
80 kHz 10.100 MHz X3A (18.100 MHz)
150 kHz 10.000 MHz X3B (18.000 MHz)
1If your K1 is already assembled, use the VFO range you recorded on page 12 of the owner's manual.

7
Two different crystals, X1A and X1B, are supplied for the highest-frequency band, which can be
either 15 or 17 meters (21.0 or 18.05 MHz, respectively)2. Identify the desired crystal using the table
below, and store the unneeded crystal. (X1 will be installed in the next step.)
Band Crystal
15 meters X1A (29.000 MHz)
17 meters X1B (26.050 MHz)
Install the four crystals at X1-X4, but do not solder yet (crystal locations are shown in Figure 2). Be
sure to use the correct crystals at X1 and X3 based on your selections in the two previous steps. Orient the
crystals so that the marked frequencies can be read on all four. Bend the leads to hold them in place.
Figure 2
Re-check the crystal frequencies, then solder and trim the leads.
Cut four 1/2" (12 mm) bare wires. Solid hookup wire or discarded component leads can be used.
Referring to Figure 2, insert bare wires into the grounding holes provided near each crystal. Fold each
wire over the top of the crystal and solder it on top. Keep soldering time below 5 seconds at a time; if it
takes longer, your iron may not be hot enough, or your iron tip may not be making good contact with the
crystal can. Solder and trim the wires on the bottom of the board.
2Both bands are excellent choices for QRP operation. 15 meters is a low-noise, long-haul DX band with a
large CW segment, and is popular during contests, including Field Day. 17 meters is also excellent for DX
work, although it has a smaller CW segment. Like the other WARC bands (30 and 12 m), 17 m cannot be
used during contests.

8
At the ends of the board you’ll find two short jumper locations, each labeled with a ground symbol
(). Use component leads to make 3/4" (19 mm) U-shaped wires for each jumper (see Figure 3). Solder
the jumpers on the bottom side, keeping the top of the U-shape approx. 1/4" (6 mm) above the board.
Figure 3
iIn the following steps you’ll prepare and install several toroidal inductors. Winding the
toroids is not difficult. However, they must be wound exactly as indicated in the instructions, or the
transceiver will not operate correctly. Use only the number of turns specified. It is not necessary to use
an inductance meter to precisely match the inductances shown on the schematic.
All the toroid cores used on the KFL1-4 board are type T37-6 (yellow, 0.37" [19 mm] in diameter). If
you aren't yet familiar with toroidal inductors, please read the information on page 13 of the K1 owner's
manual titled "Identifying Toroid Cores."
Locate the component outline for inductor L1 at the right end of the Filter board, near C21. Compare
this component outline to Figure 4, which shows two views of L1. In the next few steps you'll wind L1 and
prepare its leads, then mount it vertically as shown in the drawing at the right. Note: Leads 1 and 2 of L1
are identified for use in winding instructions, but are not printed on the PC board.
Figure 4

9
Cut a 9" (23 cm) length of the red enamel-coated wire.
To wind L1, "sew" the long end of the wire through the core 11 times, spacing the turns as shown in
the left-hand drawing of Figure 4. Each pass through the core counts as one turn. Leave at least 1/2" (12
mm) of extra wire for each lead, and trim off the excess.
Hold L1 as shown in Figure 4. Verify that lead 1 of L1 terminates on the top side of the core and lead
2 terminates on the bottom. This winding sense (or direction) is required to match the pads provided for L1
on the PC board.
Make sure that the turns of L1 are evenly spaced, and that they occupy about 80% of the core. The
winding must look identical to Figure 4, with exactly 11 turns. (Always count toroid turns on the inside of
the core to make sure you're counting passes through the core.)
iAbout 90% of all problems with kits are caused by toroid leads that are not prepared
properly. We've made it as easy as possible by supplying "Thermaleze" heat-strippable enamel-coated
wire, but you'll need to do the rest. If you read and follow these instructions carefully, you'll avoid possible
frustration, troubleshooting, and repair charges.
The goal in preparing toroid leads is to (1) remove ALL of the enamel coating on the leads; (2) tin the leads
so that a clean solder joint will result. Leads must be tinned up to the edge of core (the core itself is non-
conductive). Review Figure 4, which shows the part of the leads to be stripped and tinned.
If you have a padded vise (such as a Panavise), clamp L1 into it with its leads horizontal, ready for
heat-stripping and tinning. (Don't over-tighten the vise as this might crack the toroid core.) If you don't
have a vise, lay L1 on a flat surface with one lead bent upwards slightly.
Melt a very small amount of solder (a "blob") onto your iron tip, then place the tip and the hot solder
in contact with the toroid lead, about 1/4" (6 mm) away from the core. If the iron is hot enough, you should
see the insulation bubble and start to vaporize after 4 to 6 seconds. Remove the iron when this occurs.
Clean the iron tip completely using a damp sponge. Then hold it back up to the lead to clean off any
residual solder. Use solder wick if necessary.
Examine the lead closely using a magnifying glass; you should see bare copper wire where the enamel
was removed. If any enamel coating remains, repeat the heat-stripping procedure. An alternative is to use
sandpaper. The lead must be free of all enamel before continuing.
Tin the lead by applying a small amount of fresh solder. The solder should appear clean and shiny. If it
looks dull or is not adhering very well to the bare lead, repeat the heat-stripping procedure.
Prepare the other lead of L1 in the same manner.

10
Install L1 vertically as shown by its component outline. Pull the leads taut on the bottom of the board
and bend them slightly to hold the toroid in place. Use the magnifying glass again to verify that the part of
each lead that extends from the pad is tinned and shiny. (If not, you will not be able to solder the lead
properly. Remove L1 and re-do lead preparation.)
Solder the leads of L1. When soldering, make sure that the solder binds well to the leads--an
indication that it was properly prepared. Trim the leads.
Wind and install L2 through L6 in the same manner as L1, using red enamel wire and the turns counts
listed below. (Remember that each pass through the core counts as one turn.) The turns spacing should be
adjusted so that the winding occupies about 80% of the core, as shown in Figure 4.
__ L2, 10 turns (8" [20 cm]) __ L3, 11 turns (9" [23 cm])
__ L4, 16 turns (12" [30 cm]) __ L5, 15 turns (11" [28 cm])
__ L6, 16 turns (12" [30 cm])
iDo not use adhesives to secure toroids to the PC board. They will be supported by their leads.
T3 and T4 are toroidal transformers, with two windings (Figure 5). They use the same type of core as L1-
L6 (T37-6). They must be wound with the correct number of turns and the correct winding sense or you
may not be able to align the transceiver.
Figure 5