Elecraft KAF2 User Manual

E L E C R A F T K A F 2

A U D I O F I L T E R a n d R E A L - T I M E C L O C K

Assembly and Operating Instructions

Revision A, August 30, 2001. Copyright © 2001, Elecraft; All Rights Reserved

Introduction

The KAF2 option supplements the K2's crystal filters with effective, low-noise audio filtering. It also adds
a real-time clock, allowing you to check the time or date with a tap of the K2's D I S P L A Y button.

Audio Filter

The KAF2 includes a passive, balanced low-pass filter (LPF) that is in-circuit at all times. It provides
significant attenuation of signals above 3 kHz, including hiss, high-pitched splatter, and carrier leak­through. The LPF is particularly useful on quiet bands, when using headphones, or with small antennas.

Also included is a narrow, active band-pass filter for CW or data use. The center frequency of the filter is
tunable via two potentiometers. The A F I L switch on the K2 front panel selects either O F F (LPF only),

A F 1 (first CW filter stage), or A F 2 (both stages). The operator can choose to treat both CW filter stages as

a single setting (A F 2 ) by installing jumper W1.

Real-Time Clock

The real-time clock displays 24-hour time, as well as date. You'll find the clock convenient for field
operation since it eliminates the need to bring a separate clock. Time can be easily set using the B A N D +
and B A N D - switches. The on-board lithium backup battery will power the clock for up to several years.

Specifications

Low-pass filter Flatness: better than 1 dB, 0.5 to 2 kHz; Atten.: approx. -20 dB at 4 kHz
Band-pass filter Bandwidth: approx. 80 Hz @ -3 dB, 270 Hz @ -20 dB (two stages cascaded)
Clock Accuracy +/- 20 ppm (+/- 1.7 seconds per day) at 25 degrees C
Date Formats MM-DD-YY or DD-MM-YY; handles all calendar months and leap years
Current Drain Approx. 10 mA
Size 1.5" (L) x 1.5" (D) x 0.5" (H) (3.8 x 3.8 x 12 cm)

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Caution: Some parts in this kit can be damaged by static discharge. Before handling any

transistors or ICs, put on an anti-static wrist strap, or touch a grounded, unpainted metal surface.

Elecraft • www.elecraft.com • 831-662-8345

Parts Inventory

Ref.

Description

Part No.

Qty

BT1

Battery, 3V lithium, 20 mm dia., CR2032 or equivalent

E980039

1

C19

Capacitor, 33 pF ("33" or "330")

E530064

1

C9, C15, C16

Capacitor, 470 pF ("471")

E530080

3

C11, C14

Capacitor, .01 µF ("103"), 0.1" lead spacing

E530019

2

C3, C4, C7, C8

Capacitor, .01 µF ("103"), 0.2" lead spacing

E530009

4

C5, C6

Capacitor, .022 µF ("223")

E530056

2

C1, C2

Capacitor, .068 µF ("683")

E530081

2

C12, C13, C17, C18

Capacitor, 0.22 µF ("224")

E530079

4

C10

Capacitor, electrolytic, 10 µF

E530045

1

D1, D2

Diode, 1N5711

E560004

2

CTRL-J1

Conn., 5 pin female, 0.1" spcg., gold

E620051

1

CTRL-J2

Conn., 3 pin female, 0.1" spcg., gold

E620009

1

L1, L2

Inductor, 82 mH, 5%, shielded ("823")

E690015

2P1Conn., 5-pin male, 0.1" spcg., gold

E620052

1P2Conn., 3-pin male, 0.1" spcg., gold

E620053

1

Q1, Q2, Q3

Transistor, J309 JFET

E580009

3

R11, R12, R15-R17

Resistor, 220 ohms, 1/4 watt, 5% (red-red-brown)

E500002

5

R3, R7

Resistor, 470 ohms, 1/4 watt, 5% (yellow-violet-brown)

E500003

2

R13

Resistor, 910 ohms, 1/4 watt, 5% (white-brown-brown )

E500070

1

R14

Resistor, 2.7 k, 1/4 watt, 5% (red-violet-red)

E500005

1

R9, R10

Resistor, 10 k, 1/4 watt, 5% (brown-black-orange)

E500015

2R4Resistor, 47 k, 1/4 watt, 5% (yellow-violet-orange)

E500067

1R5Resistor, 100 k, 1/4 watt, 5% (brown-black-yellow)

E500006

1R6Resistor, 180 k, 1/4 watt, 5% (brown-gray-yellow)

E500068

1R8Resistor, 510 k, 1/4 watt, 5% (green-brown-yellow)

E500069

1

R1, R2

Trimmer potentiometer, 5K ("502")

E520009

2

RP1

Resistor network, 3.9 k, 4 resistors, 8 pins

E510000

1S1Miniature slide switch, DPDT

E640009

1U1IC, quad low-noise op-amp, LM837N

E600037

1U2IC, programmed microcontroller, PIC16C621A-04/P

E610009

1U3IC, real-time clock, NJU6355ED

E600038

1U4IC, voltage regulator, 6V, 2.5%, ZR78L06C

E600017

1W1Conn., 2-pin male, 0.1" spacing

E620054

1X1Crystal, cylindrical, 32.768 kHz

E660015

1Z1Ceramic resonator, 4 MHz, 3 pins

E660001

1

MISC

Jumper, 2-pin shorting (for W1)

E620031

1

MISC

KAF2 PC board

E100128

1

MISC

Socket for BT1

E980040

1

MISC

IC socket (for U2), 18 pins

E620031

1

HDWR

Standoff, male-female, 1/2" long x 1/4" dia, 4-40 thd

E700057

1

The table below lists all parts in the kit. Refer to the K2 manual parts lists for photographs.

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Firmware Requirements

To use the KAF2's real-time clock, you'll need main microcontroller firmware revision 2.01 or later. If you
have an earlier version (1.xx), you should have received an upgrade. You can install the firmware upgrade
during assembly of the KAF2 (as explained later), or you can install it ahead of time.

Note: The main micro is U6 on the K2 Control board. To check your firmware revision, hold any switch
when powering up the K2. When you release the switch, the revision will be shown on the LCD (left side).

Assembly

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A fine-point, temperature-controlled soldering iron (700-800 degrees F maximum) is
required to assemble the PC boards. A higher-wattage iron or one with a wide tip may damage
components, pads, or traces. We also recommended the use of a Panavise (or equivalent bench vise)
and an illuminated magnifying glass to facilitate PCB and connector assembly.

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To avoid soldering conflicts, 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.

Locate the KAF2 PC board and identify the top and bottom sides. The side of the board with outlines
of the ICs (U1-U4) and most other components is the top; the side with the "KAF2" label is the bottom. If
an assembly step does not specify top or bottom, the component should be installed on the top side.

On the top side of the board, install the two 1N5711 diodes, D1 and D2. The cathode end of each
diode has a black band which must be aligned with the banded end of its PC board component outline. The
leads of the diodes must be bent very close to the body in order to fit between the two pads.

Make sure D1 and D2 are seated flat against the PC board, then solder and trim the leads.

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The leads on small capacitors can be fragile. When handling capacitors in the following

steps, do not pull on the leads or bend them excessively.

There are two different types of .01-µF capacitors supplied. Both are labeled ".01" or "103", but they
have different lead spacing. Locate the two .01-µF capacitors with 0.1" (2.5 mm) lead spacing, as well as
the four with 0.2" (5 mm) lead spacing. Separate them into two groups.

Note: For all remaining assembly steps, you should solder and trim component leads after installing each
group of components unless otherwise instructed. Leads can be trimmed before or after soldering, but trim
them as short as possible.

On the top side of the PC board, install the four .01-µF capacitors with 0.2" (5 mm) lead spacing:
__C3, __C4, __C7 and __C8.

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Some components will be installed on the bottom of the board. These components must be
seated down onto the board as far as they'll go. In the case of capacitors with formed leads, there is
no need to re-form the leads. A small amount of lead length can remain exposed.

Install the two .01-µF capacitors with 0.1" (2.5 mm) lead spacing:

__C11 (top side of the board), __C14 (bottom side).

Trim the leads of C14 as short as possible, using flush-cutters if available. If the leads are not kept

very short, they may interfere with installation of U1 on the top side of the board.

Locate the two .022-µF capacitors, labeled "223". Also locate the four 0.22-µF capacitors ("224").

Make sure you can tell the two types apart, and separate them into two groups.

Install the four 0.22-µF capacitors ("224") on the top side of the board:

__C12, __C13, __C17, __C18.

On the bottom side of the board, install the 470-pF capacitors ("471"):

__C9, __C15, __C16.

Trim the leads of C15 and C16 as short as possible, preferably flush with the board.

On the top side, install the .068-µF capacitors ("683"): __C1, __C2.

Install electrolytic capacitor C10 (10 µF). The (+) lead of C10 must be installed in the hole marked

"+". The (+) lead is usually longer than the (-) lead. The (-) lead is identified by a stripe on the body.

Install the following resistors (top side). When installing R9 (10 k), keep the body of the resistor

elevated just slightly above the board so that it doesn’t contact the soldered leads of C16.

__R9, __R10 (10 k, brown-black-orange)

__R15, __R16 (220 ohms, red-red-brown)

__R3 (470 ohms, yellow-violet-brown)

__R5 (100 k, brown-black-yellow)

__R8 (510 k, green-brown-yellow)

Install the following resistors (bottom side). When soldering, be very careful not to touch adjacent

components with the soldering iron.

__R11, __R12, __R17 (220 ohms, red-red-brown)

__R7 (470 ohms, yellow-violet-brown)

__R13 (910 ohms, white-brown-brown)

__R4 (47 k, yellow-violet-orange)

__R6 (180 k, brown-gray-yellow)

__R14 (2.7 k, red-violet-red)

Trim the leads of R14 as short as possible so it won't interfere with the installation of U3.

4

Install trimmers R1 and R2 (5 k) as indicated by their component outlines on the top side of the board.

Install resistor network RP1 (3.9 k, 8 pins). This resistor network is symmetrical and can be installed
in either orientation, but for consistency you should orient it with the pin 1 end (black dot) toward pin 1 of
the PCB outline (round pad, also labeled "1").

Install the miniature slide switch, S1. The switch should be pressed down onto the board as far as it
will go before soldering. Use a minimum amount of heat to avoid melting S1's plastic body.

Set S1 to the OUT position.

Locate the 18-pin IC socket. One end will have a notch or other mark indicating the pin 1 end. Install
this socket at U2, with the pin 1 end of the socket toward the notched end of the IC's PC board outline.

Install the ceramic resonator, Z1. (Z1 looks like a capacitor with three leads.)

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Before handling ICs and transistors, touch an unpainted, grounded metal surface.

Install transistors Q1, Q2, and Q3 (J309) as indicated by their outlines. The installed height of the
transistors should be no more than 3/8" (9 mm). Use a minimum of soldering time (1-2 seconds per lead).

Voltage regulator U4 (ZR78L06C) has a 3-pin TO-92 package, like a transistor. Install U4 in the same
manner as Q1-Q3.

Install the quad op-amp IC, U1 (LM837N). Orient the notched or dotted end of U1 toward the notched
end of its PC board outline (pin 1 end, to the left). Double-check the orientation before soldering.

The real-time clock IC, U3 (NJU6355ED), must be handled carefully. Be sure to touch a grounded
surface before and during its installation. Install U3, noting the orientation of the notched end as you did
with U1. Verify the orientation before soldering.

Install C5 and C6 (.022 µF, "223"). C6 may be a tight fit due to its proximity to U1. Adjust C6's
position slightly if necessary, but be careful not to stress the leads.

Install the 2-pin male connector on the top side of the board at W1 as shown below. The short ends of
the pins are inserted into the board, and the long ends face up. Do not solder yet.

W1

P1

P2

5