Micro908 Kit

A re-usable control & computing platform for 
antenna measurement, audio filtering,
signal source & VFO, memory keyer ... and more !

                              ~~ News ~~

The Micro908 Kit is no longer available
... but development and prototyping continues for
an improved, next-generation version:

     (1) New reflectometer (REFL3) with improved accuracy;
     (2) Provision for new math coprocessor to give advanced measurement capabilities;
     (3) Provision for USB connection to PC for data logging, remote control and program updating; and
    (4) Provision for new graphic display, providing the pathway to display graphical Z and SWR plots on the instrument
    (5) Provision for new RF Input Card to allow precision RF measurements to be made, displayed and sent to the PC for plotting

Link908 updated to v2.2.4
     Micro908 owner Mike Hasenfratz, WA6FXT fixed a problem in his program so that once again his excellent data capture and plotting program will work with the latest Antenna Analyst releases.  Try it out!

New Operating Manual
     Take a peek at a section of the forthcoming Owner's Manual to see some fleshed-out application "use cases" for the Micro908. It's still draft, of course.

Max Supply Voltage is 12V

The max battery/power supply voltage for the Micro908 is 12V.  This limitation protects the buffer amplifier on the internal DDS-60 card. See the Builders Notes for details.

Currently building the Micro908 kit?

If so, be sure to see the Builders Notes web page for lots of helpful construction hints and corrections to the Assembly Manual.  (Not necessary for kits purchased since 2008.)

shown here with Antenna Analyst
software and panel overlay

(Click photo to see high-res view)

Production PCB
(shown without daughtercards)
(Click photo to see high-res view)

Production PCB
(shown with all 3 daughtercards)
(Click photo to see high-res view)

Link908 Screen
(showing scan results)
(Click photo to see high-res view)

AA908 Excel Plot Macro by Al Gerbens, K7SBK
(Click photo to see high-res view)

Spectrum Analysis of DDS Daughtercard

Shows second harmonic 35-40 dB below fundamental. Good signal quality is important in achieving most accurate measurement results.  DDS card has DDS Amp installed.


The Micro908 Kit is no longer available.
Research and prototyping continues on a next-gen version (see sidebar).

 Micro908 Overview Video

  Micro908 News Blog  
Read the latest news & happenings, straight from the designers!

The Micro908 is an ideal computing platform for ham radio enthusiasts and homebrewing experimenters. Designed and developed over several years, this multi-use instrument serves as a common hardware platform for a number of powerful applications:

  • Antenna Analyst "AA-908" (shown in photo at left) -- Antenna analyzer program measures SWR, R and X from 1-60 MHz. Multi-featured capabilities include Auto Scan, granular frequency control, audio output SWR indication for 'eyes-free" use, optional serial connection to PC for use of plotting utilities, field upgradeability of software, and more.

  • DSP Audio Filter "AF-908" -- This DSP Audio Filter software enables the DSPx Daughtercard to function as a high-performance audio filter for use with your existing station receiver.  It contains the same filtering software as on the Elecraft K2DSP ... and more! 

  • Full Function VFO Program -- Moderately-featured VFO program, with memories, frequency offset and scaling.  (Drive your SoftRock with your Micro908!)

  • Other software in development ...

    • Digital Modem Controller "DM-908" -- Software for the Micro908 serves as a digital modem allowing you to work PSK-31 without a need for the PC.  Just connect your SSB rig and a standard PS2-style keyboard to the Micro908, and you'll be ready to send and receive on the digital modes.

    • Deluxe Memory Keyer -- Place your Micro908 in-line between your paddle and transceiver and this software package serves as multi-function keyer.

    • Morse Keyboard -- Place your Micro908 in-line between your standard PS2/USB keyboard and transceiver and this software package allows you to send Morse code at typing rates.

Latest SoftwareAA908 v6.0g and AF908 v1.2d
We've added a big new Diagnostic menu section under the Config pushbutton.  Explore it and have fun.  Notably, there is a Keyboard Test menu item that will echo characters from the keyboard connected to the modified motherboard.   Be sure to read the Release Notes for our latest software release here, as they tell the whole story of features added over the release history.  Refer to the Software Archives for all the older software releases in case you'd like to go back to prior releases.

            Latest Production AA908 Antenna Analyst Software:
                    Binary loadable image (AA v6.0g) <== Unzip to create the S19 file that you load into the Micro908.
                    Zipped Source Code (AA v6.0g)
                    Release Notes (AA v6.0g)

            Latest Production AF908 Audio Filter Software:
                    Binary loadable image (AF v1.2d)   <== This is the S19 file that you load into the Micro908.
Zipped Source Code (AA v53b-AF_v12d) <== The source for AF908 is combined with older AA_v53b
                    Release Notes (AF v1.2d)

REFL -- Sneak peak at the new reflectometer and measurement sub-system for the Micro908 Antenna Analyst.  It's still in development, yet initial tests look promising for providing a high-performance upgrade to the AA-908 capabilities.

Invaluable Utility Programs for the Micro908 ...

Link908 -- Link908 is another software program for your PC that collects and plots the SWR and impedance data collected by the Micro908 Antenna Analyzer. (The other such program is the AA-908 Plotter, described below.)  Mike Hasenfratz, WA6FXT created Link908 and has proved to be of great value to Micro908 owners. Link908 has been recently been updated to support the higher frequencies offerred by the DDS-60 card in currently-shipping Micro908 Kits, as well as some of the other advanced features (increased band selections, scan rates, etc.)

908Loader -- Dave Gwillim, KB2TQX wrote this "smart terminal" program we call "908Loader" that  automates a few things that have tripped up some Micro908 users when attempting to load new software into the instrument using TeraTerm. Most importantly, 908Loader checks the checksum of each line sent to your Micro908 to ensure it is valid code, it automatically incorporates the line delay, and it only allows S19 binary files to be sent to the instrument. (Previously with TeraTerm, if you didn't have the delay set properly, or if you mistakenly selected some file besides the .s19 program file, you would probably hose the bootstrap loader on the Micro908 and need to get it reprogrammed.)   Further, the settings for your serial port and S19 file location are saved and used when starting the program the next time.  Give this 908Loader program a try and let us know how it works out for you.  Just download the zip file and unzip it to any convenient folder.  I placed a shortcut icon on my own desktop and access it every day here in the shack.  Thanks for the initiative Dave!

AA-908 Plotter Program -- Al Gerbens, K7SBK provides a wonderful Excel macro program that takes the scan data produced by the Micro908 "Antenna Analyst" and automatically generates a plot of the SWR, Resistance and Reactance.  A new feature of Smith Chart plots has been recently added. With a simple keystroke and pointing to the data file, the macro generates a colorful scaled graph that shows the results the antenna analyzer scan on your PC screen.  Great for comparing antenna performance, archiving results and seeing other dimensions of your antenna configuration.

Palm Link908-- Ron Pfeiffer has created a Palm PDA software program to control and plot scan data of Antenna Analyst.  Just connect the Palm to the Micro908 and control it just as done in the Link908 program for the PC. (Now supports the new 60 MHz frequency ranges of the DDS-60 card!) 

AA908 Calculator Spreadsheet (for AA908 v6) -- Ever wonder what those numbers are being sent out the serial port when Debug Mode is turned on?  Well, take a look at this spreadsheet and you'll get an idea of how all the internal math is done in the calc.asm module of the source code.  In fact, you can follow along in the sourse while looking at the equations in the spreadsheet to get a good idea. Just collect the data in your TeraTerm window, "cut" out the appropriate lines and "paste" them into the proper column of the spreadsheet.  There are a couple of examples already present. You'll need to think it through a little before I get a chance to explain step-by-step how it's done, but the answers are all there.  BTW, there's a neat function in Excel called HEX2BIN (or somesuch) that let's us enter hexidecimal numbers, and have the spreadsheet display results in familiar hex format too.  (You may need to have a data option installed in Excel to have this function present ... else you get a #NUM error.) 

AF908 Overlay Graphic -- Are you looking for a modified overlay graphic that reflects the AF908 filter?  If so, this PDF is file is for you!  Just download it, print it, laminate it, cut out the holes and paste it place over the existing AA908 overlay.  (In order to get the correctly-sized printout, be sure to select the "No Scaling" option in the printer control window.)

Flash Programming App Note -- Bob K7HBG found this informative application note on the Freescal website (suppliers of the 68HC908 processor we use as the heart of the Micro908) that describes very easy ways to create your own programmer for the HC908 Daughtercard.  Homebrewers and software experimenters would want to do this to modify/customize their HC908 card bootloader, and other things.  Further, he has a circuit diagram that explains what he has worked up to do his own bootloader re-programming and mods.  Thanks for sharing this Bob!

Calibration & Accuracy Study -- Some Micro908 Antenna Analyst owners have been studying the slight measurement drifting and accuracy characteristics of the instrument.  The drift is currently attributed to the heat generated by the DDS card affecting the reflectometer diodes, and the accuracy is somewhat affected by the limitations of 8-bit math computations and the inherent "uncertainty" of needing to simultaneously measure phase and magnitude of the reflectometer signals.  Read all about it inside, including some photos and software improvements that are in progress.

AF-908 Debugging Guide -- Having trouble getting your DSPx card working with your Micro909 AF-908?  Well, here are some debugging tips from Steve Holton, N1NB, who is the guy who wrote the DSP Audio Filter control program for the Micro908.

Backlight Control for LCD -- Here's a simple modification that will greatly increase the usability of your Micro908 instrument in low-light conditions. 

Technical Discussions: 

Manuals & References:

  • AA908 Operating Manual -- This manual provides a complete and current guide to operating the Antenna Analyst: use of all the controls, explanation of the different modes of operation, and includes the colorful Quick Reference Sheet.

  • Way To Use the Micro908 Antenna Analyzer -- Describes various ways to set up and use the analyzer to perform measurements beyond just standard impedance ...L, C, Q, transmission line characteristics impedance, transmission line loss, transmission line stub lengths, transmission line velocity factor, and more.

  • Micro908 Technical Reference Manual  -- This manual provides theory of operation, schematics and lots of good background material on the design of the Micro908. 

  • Loading Software into the Micro908 -- Describes the simple steps to be done in order to load updated software into your Micro908 instrument.

  • Calibrating the Antenna Analyst -- You'll need to calibrate the AA908 after first asembling the kit, and sometimes when software updates are made, and always when the DDS signal has changed.  

  • Assembly Manual:
       Version 1 Online Manual -- This online version shows all the hi-res color
              images of the photos used in the B&W printed manual.
       Version 1 PDF -- This original version applies to the first shipment of the kit
              in September 2004 (with MAR and MAV devices on the DDS
              Daughtercard). [2 MB download]
       Version 2 PDF -- This version applies to those Kits shipped in
              February (pcb marked 'A2') and September 2005 (with DDS Amp in
              DDS Daughtercard sub-bag).  [6 MB download!]
       Version 3 PDF -- This version applies to those Kits shipped in Round 5 kitting
              during Nov-Dec 2006
       Version 4 PDF -- This version applies to kits shipping with the updated Rev B pcb (no mods required!)

  • Quick Reference Sheet -- A very useful sheet that diagrams the Menu structure of the Antenna Analyst software.

  • Schematic -- The Rev B1 schematic of the project.
    (Note: Lines may display somewhat ragged on a computer display, but the increased resolution on a printout produces a nice-looking schematic.)

Micro908 Enclosure Resources -- Here are some files that will be helpful if you are building your own custom enclosure or labels. These file should be perfect for those wishing to design custom label panels for the AA908, or any other Micro908 project coming along.

1) AA908 Overlay Proof.PDF -- This file shows an enlarged shot of the actual overlay panels (top, side, end), and most importantly, the accurate dimensions for each on page 2.

2) AA-908 drilling dimensions.jpg -- This file shows the drilling dimensions for the enclosure itself.

3) FrontPanel v3b.ppt -- PowerPoint graphics slide to allow you to make your own custom front panel ... make the dimensions the same as those listed in #1 above.

4) Enclosure dimensions -- We use the Pac-Tec LH57-130 for the current Micro908 enclosure.  Click here to see some quick dimensions and to download the spec sheet for this case.

MAV-11 Orientation -- If your "NJQRP DDS Daughtercard" (used prior to the DDS-60 availability) has a MAV-11 device for the final RF amplifier, please note the correct orientation for the "dot" for the output pin as being oriented downward on the pcb.  See the photo.

Description -- This link provides a good overview of the kit and its capabilities. Includes block diagram.

Builders Notes -- A collection of construction Tips and Technique, and various Errata for the kit.  This web page is important to see if you are currently building your Micro908 Kit.

FAQ -- Frequently Asked Questions ... and answers!

Micro908 Photo Album
See photos of the production kit.

Prototype Photo Gallery -- A collection of views inside and around early versions of the kit.

Micro908 Yahoo Group -- We maintain a Yahoo Group discussion list for owners to post Q&A about the Micro908 kit. Click the link here to address a new message to the Micro908 list. 

Micro908 Email Archives
-- Check the Micro908 Yahoo Group

A feature-length article concerning the Micro908 and the Antenna Analyst was in the issue #2 of HOMEBREWER Magazine

Micro908 "Antenna Analyst AA-908"   
Several years ago, N2APB and N2CX embarked on a journey to develop a low-cost antenna analyzer that would sweep the ham bands with a micro power transmitter and measure the resultant SWR of an antenna system. We presented the original design of the Analyzer at various QRP forums circa 1998-2000 and evolved the hardware platform several more times in the Digital QRP Homebrewing column of QQ magazine (proto 2 and proto 3).

The hardware design is complete and is now called the Micro908.  It is a production-quality kit and has been available from the AmQRP Club since August 2004.

"The Micro908 is the common hardware platform
for many projects coming from 
the AmQRP design teams."

What this means is that you get the Micro908 Kit, load it with FREE SOFTWARE that is downloadable from the AmQRP web pages, and you have a brand new instrument or radio accessory. Because the Micro908 is based on the NJQRP "HC908 Daughtercard" module, you don't need any special hardware or cable to load new software into the unit.  You just connect the Micro908 up to your PC with a standard serial cable and send a new software program to the device. 

The Micro908 is a flexible and re-usable control platform for ham radio projects. The Micro908 platform is designed to be easily operated on the bench as well as in hand while portable. It is comprised of a single 5” x 5” printed circuit board containing all components, connectors, controls, a 2x16 character LCD, and three daughtercards. The 5.5” x 7” x 1.5” plastic enclosure is also large enough to hold an 8-cell AA battery back enabling convenient field use.  A number of standard ham radio peripherals may be connected to the Micro908. You can plug in an antenna, paddles, a PC-style keyboard, headphones, an audio line to drive an SSB transceiver, a keyline to drive a transmitter, your rig's audio in/out signals, and custom control lines via an auxiliary jack. 

A complete Micro908 motherboard assembly
Shown without the enclosure and including the optional DSPx daughtercard (lower right)

The Micro908 is built around three modular daughtercards available within the homebrewing community: 

(1) The HC908 Daughtercard plugs in as the main computing engine for the platform and provides flexible programming, field updates, powerful processing and a multitude of input/output lines for controlling all the devices in the unit. 

HC908 Daugtercard -- main control unit for the Micro908

(2) The DDS-60 Daughtercard serves as a precise and accurate signal source that is programmable by the HC908. This plug-in module gives the Micro908 platform the ability to serve as an audio and RF signal source for testing and network analysis.

DDS-60 Daughtercard -- programmable RF signal source for the Micro908

(3) The KK7P DSPx Daughtercard is an optional module that gives the Micro908 platform a powerful signal processing capability suitable for serving as a digital modem for PSK31, PACTOR and other digital modes of operation. This is the same DSP module as optionally used in the Elecraft K2 HF Transceiver as an audio filter, and in the DSP-10 software defined radio project from TAPR. When coupled with the HC908 controller, the DSPx daughtercard makes a formidable portable computing platform.

KK7P DSPx Daughtercard -- provides powerhouse signal processing for advanced audio features in the Micro908

Block Diagram of the Micro908


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Page last updated:  March 1, 2014