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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
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 leak-
through. 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
(first CW filter stage), or
A F 1
a single setting (
) by installing jumper W1.
A F 2
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
and
switches. The on-board lithium backup battery will power the clock for up to several years.
B A N D -
Specifications
Low-pass filter
Band-pass filter
Clock Accuracy
Date Formats
Current Drain
Size
i
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
E
L E C R A F T
switch on the K2 front panel selects either
A F I L
(both stages). The operator can choose to treat both CW filter stages as
A F 2
Flatness: better than 1 dB, 0.5 to 2 kHz; Atten.: approx. -20 dB at 4 kHz
Bandwidth: approx. 80 Hz @ -3 dB, 270 Hz @ -20 dB (two stages cascaded)
+/- 20 ppm (+/- 1.7 seconds per day) at 25 degrees C
MM-DD-YY or DD-MM-YY; handles all calendar months and leap years
Approx. 10 mA
1.5" (L) x 1.5" (D) x 0.5" (H) (3.8 x 3.8 x 12 cm)
•
www.elecraft.com
K A F 2
D I S P L A Y
O F F
•
831-662-8345
button.
(LPF only),
B A N D +
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Table of Contents
Related Manuals for ELECRAFT KAF2
Summary of Contents for ELECRAFT KAF2
-
Page 1: Specifications
D I S P L A Y 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 leak- through. -
Page 2: Parts Inventory
E620054 Crystal, cylindrical, 32.768 kHz E660015 Ceramic resonator, 4 MHz, 3 pins E660001 MISC Jumper, 2-pin shorting (for W1) E620031 MISC KAF2 PC board E100128 MISC Socket for BT1 E980040 MISC IC socket (for U2), 18 pins E620031 HDWR Standoff, male-female, 1/2" long x 1/4" dia, 4-40 thd... -
Page 3: Firmware Requirements
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. - Page 4 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"...
- Page 5 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").
- Page 6 (2.5 mm) or less. Be careful with the crystal's leads, which are very thin and may break if stressed. The KAF2 date display format is normally MM-DD-YY. If you prefer DD-MM-YY, solder a short wire jumper at W2. The pads for W2 are located on the bottom of the board, near pin 10 of U2.
- Page 7 Check the revision of your Control board, which appears at the bottom right. If your Control board is revision A (or earlier, i.e. XA, XB, XC), you'll find that the component outlines for the KAF2 connectors (J1 and J2), as well as the audio filter module itself, appear on the bottom side of the board. DO NOT install J1 and J2 on the bottom side of the Control board.
-
Page 8: Installation
(as viewed from the K2 front panel) will be replaced with the male-female standoff supplied with the KAF2. Once the KAF2 is in position, the original screw and lock washer will be used to hold it in place. Thread the 1/2" (12 mm) male-female standoff through the mounting hole in the control board (near C29) and into the front panel standoff. -
Page 9: Band-Pass Filter
Alternatively, you can use an audio spectral-analysis program to do pitch matching and filter alignment Make sure S1 on the KAF2 is in the IN position, enabling all audio filter circuits. (Also make sure that jumper W1 is not installed.) Then hold the K2's switch. -
Page 10: Volt Battery Installation
Turn the K2 off. Remove the top cover or left side panel to gain access to the KAF2. The (+) side of the 3-volt battery must be oriented toward the "+" symbol on the KAF2 board. The (-) side must face the left side panel of the K2. Insert the battery in its socket, under the spring clip. DO NOT use long-nose pliers to hold the battery--this will short the + and - sides of the battery together. -
Page 11: Low-Pass Filter (Lpf)
I.F. amplifier. Under these circumstances, the effect of the LPF may be less noticeable. After installing the KAF2, you may find that you need the preamp less often. This is due to the improved audio signal-to-noise ratio provided by the LPF. Having the preamp turned off is most beneficial when the K2 is used in close proximity to very strong stations, such as during Field Day, or if you live in an area with high-power HF broadcast stations. -
Page 12: Using The Real-Time Clock
Bypassing the Audio Filter The audio filter can be bypassed by setting S1 on the KAF2 module to the "OUT" position. In this setting the real-time clock will still work (if enabled), but the low-pass and band-pass filters will be totally disabled. -
Page 13: Troubleshooting
Receiver noise heard when in time or date display mode: This is normal. The main microcontroller polls the KAF2 for time or date information once per second, waking up all option module processors, which generates noise that is audible at some frequencies. The K2 does not mute the receiver when date or time is being displayed, because the operator may want to use WWV or some other on-air time source for clock setting. -
Page 14: Circuit Details
Refer to the schematic diagram, page 16. The filter circuits of the KAF2 are inserted between the receiver's product detector and AF amp stages. This is a fairly low-level point in the receive chain, so to maximize signal-to-noise ratio, a very low-noise op- amp is required (U1, LM837). - Page 15 (This page intentionally left blank)
- Page 16 0.22 = On bottom of PC board. 1. R18 and R19 on the Control board (which may be jumpers) must be removed when the KAF2 is installed. Elecraft KAF2 Audio Filter/RTC 2. Install W1 to skip the first-stage band-pass filter output (AF1).