Revised 3-21-2014
The Elecraft K2 amateur radio transceiver kit was first introduced in the late 1990's. At the time of this writing it is still in production, with well over 7,000 units sold. Its performance is excellent even by today's standards.
One of the key features of the K2 is the flexibility with which it can be configured. Users can purchase various modules to obtain the options most important to them. In addition to options from Elecraft, a number of aftermarket and homebrew accessory circuits have been developed and installed.
The K2 microphone connector wiring can be configured to match the wiring of a number of popular microphones. This feature is implemented via a dual-row header on the K2 front panel board. One row of pins is connected to the radio's internal circuits and the other row of pins is connected to the individual microphone connector pins.
Accessing this header for reconfiguration requires some disassembly. Ken Kaplan, WB2ART, and Gary Hvizdak, KI4GGX, developed an innovative product that greatly streamlines the process, the K2 Internal Mic Adapter (IMA.) With the IMA installed, the microphone connector wiring can be reconfigured by simply removing the left side panel, rearranging some plug-in jumpers, and replacing the panel.
Another popular addition is a fixed-level audio output circuit developed by Don Wilhelm, W3FPR. This circuit provides an audio signal to the soundcard input of a computer for data communications or for decoding Morse code (CW). The audio level is not affected by the volume control setting.
Yet another popular accessory is a CW tuning indicator circuit developed by Bob Wolbert, K6XX. This circuit provides a visual indication when the K2 is tuned to within approximately 25 Hz of a received CW signal.
A circuit that enables a computer to key the K2 for transmitting CW is another popular addition. Page 99 of the K2 owner's manual shows an example circuit that can be used to accomplish this.
Physically mounting the various additional circuit boards to implement all these functions in the K2 can be challenging. Another issue is the need for one or more connectors to make the necessary signals available outside the radio, preferably without drilling any additional holes.
From recent discussions on the Elecraft reflector, a spare pin on the microphone connector can be used for bringing out the fixed-level audio output signal. Why not use an additional pin for the computer-generated CW keying signal? Then there would be no need for any additional connections outside the radio.
Carrying it a step further, why not consolidate all these circuits and features into one place? That is the purpose of this project, the K2 Miscellaneous Accessory Board, or MAB for short.
The MAB is mounted on the K2 front panel board as shown in this photo.
Here is a schematic diagram of the MAB.
The MAB can be used either with or without the Internal Mic Adapter. When used without, the microphone wiring is configured for the default Elecraft microphone wiring.
At the time of this writing, three MAB prototypes have been fabricated and are completely functional.
Due to time constraints I have no plans to market the MAB in any form, including parts, kits, or bare boards. If someone should want to take on such an effort I would have no objections, though.
Complete project details including options, component procurement information, and assembly/installation instructions, including many additional color photos, are provided in the project manual. The project manual can be freely downloaded from one of the links below.
ExpressPCB printed circuit board fabrication files can also be downloaded.
These files contain sufficient information for a competent homebrewer to build a MAB. The files will be updated on occasion as improvements or corrections are identified. If you plan to build a MAB it would be a good idea to verify you have the latest versions.
If you have built a MAB, please provide any feedback that you may have such as corrections or suggestions for improvement. An email can be sent to me via the Elecraft reflector.
Elecraft ® is a registered trademark of Elecraft, Inc.
Rework Eliminator is a trademark of Ken Kaplan (WB2ART) & Gary Hvizdak (KI4GGX).
The Rework Eliminator™ K2 Internal Mic Adaptor circuit diagram & circuit board layout, are the intellectual property of Ken Kaplan & Gary Hvizdak. Copyright © 2007 – 2014, all rights reserved, used with permission.
The files linked below can be downloaded for additional information.
K2_Misc_Accessory_Board_V1.1_Manual_3-20-2014.pdf The project's background, description, parts procurement, assembly, installation, and alignment are described in detail in this project manual. The file size is approximately 5 Mb.
K2_Misc_Accessory_Board_V1.1.sch ExpressPCB schematic file.
K2_Misc_Accessory_Board_V1.1.pcb ExpressPCB board layout file, needed to order boards from ExpressPCB.