DSP Audio Filter Program
for the Micro908

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Micro908  DSP Audio Filter


AF908 is a software package for the Micro908 kit, produced by the American QRP Club, that enables the Micro908 to perform as an audio filter utilizing the popular KK7P DSPx Daughtercard. This daughtercard is an optional component in the Micro908, and when combined with the AF908 control software, it serves as a free-standing, portable and extremely programmable DSP that can be used to enhance the audio performance of an amateur radio receiver.  

[NOTE:  You must have the DSPx Daughtercard installed on the Micro908 motherboard connectors J8 and J9 for the Micro908 to run the AF908 software and to perform as a DSP Audio Filter.]

The AF908 software runs on the Micro908, providing the user interface for control of the instrument and for control of the internal DSPx card.  Two fully-functional DSP audio filter programs are also included that allow the DSPx card to provide its comprehensive filtering capabilities. One filter program provides capabilities similar to the Elecraft K2s KDSP2 filter (which also uses the DSPx daughtercard): fully-programmable audio filters for CW, SSB and data (RTTY, PSK31, AMTOR, et al) .   The other filter program provides a robust suite of DSP filter programs, such as a BFO, an LMS denoiser, a Wiener-filter autonotcher, and other filters using multi-rate processing, adaptive filtering and frequency shifting techniques.

Once one or more DSP programs have been loaded into the nonvolatile memory of the Micro908, the platform becomes a fully-functional DSP filter that can operate independently of a PC.  In addition, the tools necessary to modify and develop your own DSP applications are included in the package.

Block Diagram of the Micro908 AF908 Digital Audio Filter

As can be seen above, AF908 software does not utilize any of the RF paths in the Micro908 used previously by the Antenna Analyst software, nor does it require the DDS card. The AF908 control program running on the HC908AB32 control processor only utilizes the DSP daughtercard, the SEEPROM nonvolatile memory (for storage of the programs to be run on the DSPx card), and the user interface hardware of the instrument itself (pushbuttons, LCD, dial, and audio paths.

After the preliminary instructions for getting the Micro908 updated and the AF908 software installed, this User Manual will guide you on how to run a simple DSP program and verify that all the components of the AF908 system are working. The manual will then cover the basic operations of the two DSP software components: DSP908 and ASP.

There are many options available in the AF908 software package, some of which will only be used by a few users or used very infrequently, so we have included a complete reference covering all the available options. Manual appendices describe the contents of the AF908 package, the default values for all the options, information on developing DSP programs for the Micro908/AF908 system, and information on the format and protocols for downloading DSP programs to the Micro908.

AF908 User Manual

The User Manual, written by Steve Holton, N1NB, provides a complete description of the installation and use of the AF908 software.  (Note, a minor pcb trace modification is required before you can install and use the DSPx daughtercard.  See the appendinx in the Manual for the easy steps required for this.)

        Download AF908 User Manual
(Right-click link and "Save target as ... "  to your computer)


1) You must download and install the AF908 software on your Micro908 in order to run the DSP audio filter capabilities.  Get this software on the Micro908 main page.  The AF908 "s19" file is loaded into your Micro908 platform as you have normally done when installing updated software.  (See the section for "Loading New Software" in the User's Manual.)

2) You must also download the "DSPterm.exe" program that runs on your PC, as well as the DSP files that get loaded by it.  You should place this file in a new folder named "DSPx" (for example). DSPterm may be run by double-clicking the filename in the Windows File Explorer window, or for more flexibility as described in the User Manual, in a Command Prompt/DOS window.

          Download DSPterm.exe and  Download DSPimage.exe
(Right-click each link and "Save target as ... "  to your computer)           

3) Five DSP programs (DSP908.exe, ASP.exe, C1SIN.exe, C1SIN2.exe and C1FIR.exe) are provided. For simplicity, these five DSP programs should all be placed in the same directory as used for the DSPterm and DSPimage executables in step 2.

          DSP908.exe      ASP.exe      C1SIN.exe      C1SIN2.exe      C1FIR.exe
                    (Right-click each link above and "Save target as ... "  to your computer)

4) If you are a software developer, you might wish to modify the AF908 source code that Steve Holton  is making freely available (for personal, non-profit use).  You can get these source file in the Software section on the Micro908 main page.


Steve Holton, N1NB and George N2APB are available on the Micro908 reflector to answer questions about installation and operation.

Again, thanks very much to Steve for his massive and near-single-handed effort in making the AF908 project a reality.  And thanks too to Lyle Johnson, KK7P for his guidance in the project and helping us to use his DSPx Daughtercard in the Micro908.

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These pages are designed and maintained by George Heron, N2APB
Page Last Updated:  March 28, 2005