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P. O. Box 2163

Nevada City, California 95959-2163

W9GR Digital Signal Processors

As Published in QST Magazine and the ARRL Handbook

Entire contents copyright (c) 1997-2012 by Quantics

updated November 2012

We are sorry to announce that the DSP-3 digital signal processor is SOLD OUT! Texas Instruments, the manufacturer of the DSP CPU and audio codec chips we use, has obsoleted these parts. So, since we can't buy the key parts of the DSP-3 anymore, there will be no more DSP-3s.

I really would like to do a DSP-4, using a more modern DSP chip that would hopefully stay in production for more than a few years. I've been planning on doing one since the DSP-3 went out of production. Unfortunately, many things have been distracting me from doing a DSP-4 design - more construction projects (barn and driveway), my day job (designing digital TV transmitters), etc. I can't really put a timetable on the DSP-4 development or even guarantee that it will ever happen. All I can say right now is that it is something that I would like to do. So, keep an eye on this web page, and check in every six months or so to see if I have anything to announce.

We will leave this web page up, even though it describes a product which is no longer available. Most or all of the features in the DSP-3 will be offered in the DSP-4, along with some new features.

If we receive any more orders for the DSP-3, we will have to return them to you. Thank you for your patience in waiting for the DSP-4!

73, Dave Hershberger, W9GR

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Front Panel ImagePowerful Digital Signal Processing: the W9GR DSP-3 LOW COST DIGITAL SIGNAL PROCESSOR KIT

What is this thing? It's a powerful digital signal processor ("DSP") using advanced algorithms to remove noise and other unwanted interference from voice and data communications signals. It is sold in kit form. It connects between your ham radio's audio output and your loudspeaker.

These links will take you to various places on this web page:

These links will take you to other Quantics web pages:

If you haven't used Adobe's Acrobat, it presents the PDF file in a magazine-like format. You can look at a multiple page document, zoom in, zoom out, look at embedded graphics, all with very good resolution. With Acrobat, you can also print out the DSP-3 schematic in any size. The viewer is a free download from Adobe and is available in several formats: UNIX, Windows, OS/2 and Macintosh. PDF files are quite universal. Just use the link below and download your flavor of Acrobat and then download the PDF files from this page and to view them. (Note: if you just click on the PDF files above, Acrobat will load them immediately. But if you SHIFT-click, you can download the PDF file to your hard disk for later viewing.)

acrobatDownload free Adobe Acrobat reader

Would you like to hear some of the amazing things this DSP can do to clean up crummy radio signals? What follows are some sound (.WAV) files (sound bytes!) you can download and listen to. Each of these sound files contains several seconds of unprocessed audio, followed by the same audio after it has been processed through the DSP. So what you will be hearing will be a "before/after" comparison. These files are short to keep transmission time down and file size moderate.

All of these files are 8 bits, 8 kHz sampling, also to keep file sizes down. (Some older sound cards, which do not have lowpass reconstruction filters, may produce "birdies" when playing these files - these birdies are not produced by the DSP.)

(To play these clips, your web browser will have to support sound files, and your computer will need a sound card and speakers. If you have a sound card but your browser doesn't support sound, you can always download these .WAV files and then play them later, outside of your browser.)

DSP-3 features:

The 18 DSP-3 functions are:

  1. Simultaneous Noise Filter (QRN reducer) & Automatic Notch Filter with selectable AGC
  2. Optimized Noise Filter (QRN reducer) with selectable AGC
  3. Optimized Automatic Notch Filter with selectable AGC
  4. 2.1 kHz narrow voice FIR filter
  5. 1.8 kHz narrow voice FIR filter
  6. North American RTTY filter (2125/2295 Hz)
  7. European RTTY filter (1275/1445 Hz)
  8. HF packet filter (1600/1800 Hz)
  9. SSTV Filter (1200-2300 Hz)
  10. DTMF Decoder with tone playback memory
  11. CTCSS Decoder & Squelch with tone playback memory
  12. 400 Hz CW filter, 100 Hz BW
  13. 400 Hz CW filter, 50 Hz BW
  14. 600 Hz CW filter, 100 Hz BW
  15. 750 Hz CW filter, 200 Hz BW
  16. 750 Hz CW filter, 100 Hz BW
  17. 750 Hz CW filter, 50 Hz BW
  18. 1000 Hz CW filter, 100 Hz BW

NOTE: All CW filters are tunable!

I'd feel NAKED without my DSP-3! W9GR uses his own DSP-3 all the time, and says, "Once I was moving some things around in the shack and I didn't have the DSP-3 in line. I had this terrible feeling of 'nakedness' - that if a carrier came on the frequency, I would actually hear it! And if a weak station came on, I would actually have to listen to the noise!" Don't go naked - "cover yourself" with a W9GR DSP-3!

It's best to be able to leave a DSP in line all the time, rather than waiting for noise or interference to appear before switching it in. The DSP-3 has been optimized to sound good with both strong and weak signals. Many hams have complained about other DSPs, which add resonances, strange audio tones, or "rain barrel" sound effects to voice signals. Because of these unpleasant artifacts, some hams leave these other DSP units switched "out" until they are really needed.

Separation Bar

Thousands of amateurs have built the W9GR digital signal processor since it first appeared as a feature article in the September 1992 issue of QST. Now an even more powerful and versatile version of the DSP has been developed, and it is still low cost. You can save money by building this kit yourself and have a DSP superior to units costing twice as much! Even the high priced DSPs do not have the ability to decode CTCSS and DTMF tones!

Brief Description:

The W9GR DSP-3 filter is a DSP audio filter which goes between your receiver's audio output and your loudspeaker or headphones. A LED display indicates audio level, or in the tone decoder modes it indicates DTMF and CTCSS tones. Modes are selected by a front panel rotary switch, and options are selected by a rear panel toggle switch. The DSP operates from your 12 volt DC power supply (not furnished).

The W9GR DSP-3 filter hardware uses a 13 bit A/D and D/A converter with switched capacitor filters for antialiasing and analog reconstruction. This results in a much wider dynamic range than earlier W9GR DSP filters, which used 8 bit converters. The primary advantage to having more bits is for CW operators: the ability to pick out weak CW signals amidst strong QRM.

The first three DSP functions are different combinations of noise reducers and automatic notch filters, using the Widrow-Hoff LMS adaptive filtering algorithm. The noise reducer modes are most effective against hiss and thermal noise but also reduces impulse noise and static crashes. These modes reduces listener fatigue and are recommended for long-term monitoring. The automatic notch mode eliminates multiple carriers very quickly, within a few milliseconds. Tuner-uppers, CW interference, carriers, and other forms of undesired audio tones are quickly eliminated. If a carrier comes on your frequency, all you will hear will be a subtle "click" as the automatic notch acquires.

These three modes include a defeatable digital AGC, which keeps the output level constant over variations of up to 30 dB.

Two "brick wall" narrow SSB voice filters (1.8 and 2.1 kHz) give you extra selectivity for overlapping adjacent channel QRM.

A selection of FSK filters improves copy of RTTY, AMTOR, HF packet, etc. in the presence of noise or QRM.

A special SSTV filter improves performance in that mode without group delay distortion.

A DTMF decoder uses the LED display to tell you what "touch tones" you are hearing. The last 16 decoded DTMF tones can be "played back" from the DSP's memory.

A CTCSS decoder uses the LED display to tell you what "PL" tones are being used. The last 16 different decoded CTCSS tones can be "played back" from the DSP's memory.

There are seven CW filters with various center frequencies and bandwidths. Any of these filters can be tuned down to as low as 70% of the nominal center frequency.

The CW, FSK, narrow voice, and SSTV filter firmware programs are all linear phase bandpass filters. Linear phase filtering, which is a significant advantage of DSP, allows filter bandwidth to be narrower than conventional filtering for a given maximum CW speed or data rate.

The parts kit includes a finished double sided printed circuit board with silk screen and solder mask, all PC board and front panel components, IC sockets, and a CPU chip preprogrammed with the DSP firmware. A cabinet and DC power supply are not included with the basic kit.

For those who prefer not to do their own metalwork, a custom made steel cabinet with silk screening is available.

We recommend that builders of this kit should be able to solder, identify components, and construct a PC board from a schematic and parts list.

The size of the box (less protuberances) is 1.5" high by 5.5" wide by 6" deep.

This document is for informational purposes only. QUANTICS MAKES NO WARRANTEES, EXPRESS OR IMPLIED, IN THIS SUMMARY.

Here's what the back of the unit looks like: Rear Panel Image

And here is the all-important view of the real "guts" of the W9GR DSP-3: Internal view of PC board

To order the DSP-3, please send us a prepaid order via the regular mail (you know, the slow US Postal service, a.k.a. "snail mail"). We are too small to take credit cards and/or to offer an 800 number for telephone orders. An order form follows - to make things easy, you can print it out (with a fixed width font such as Courier), fill it out, and mail it in. REMINDER: the DSP-3 is sold out - please do not send in this order form!

  • Click here to see just the order form on its own page (it will be easier to print this way)
  •                              O R D E R   F O R M
    Name:          ____________________________________ Ham Call: _______
    E-mail: (to inform you when your unit ships. You will NOT be spammed.)
    Address:       ____________________________________________
    City, State,
    Zip:           ____________________________________________
    Item                               Price          Quantity       Total
    DSP-3 Kit                         $149.00         _____          _____
    Custom metal cabinet for DSP-3     $19.00         _____          _____
    (does not fit earlier kits)
    California residents add 7.375% tax                              _____
    Shipping & Handling                                              _____
    In the USA and Canada:
    $7.00 for one or two kits with or without cabinet;
    $3.50 for each additional kit with or without cabinet.
    Outside the USA and Canada:
    $20.00 for one kit with or without cabinet;
    $10.00 for each additional kit with or without cabinet.
    For cabinets ordered separately in the USA & Canada:
    $5.00 for the first cabinet; $2.50 for each additional cabinet.
    Outside the USA and Canada:
    $15.00 for the first cabinet; $7.50 for each additional cabinet.
    Total enclosed                                                   _____
    All prices quoted are for U. S. funds drawn on a U. S. bank and are
    subject to change without notice. California residents must add 7.375%
    sales tax. Send orders to:
                                P. O. Box 2163
                     Nevada City, California  95959-2163

    What if I build it and it doesn't work?

    There are extensive troubleshooting instructions included with the kit documentation. But, if that isn't enough to help you get it going, we do have a "flat rate" debugging service available. For a flat rate of $40.00, we will get the unit working for you. Abuse is excepted! This offer does not apply if you have driven over the unit with a backhoe! Most of the time, we find that the problem is defective soldering. But, if we find that there was a bad part supplied with the kit, we will return the debugged unit to you, with your $40.00 check uncashed. See details in the DSP-3 Kit Instructions.

    What do users say?

    Absolutely bloody AWESOME!.............OH BOY!! I am not kidding: this filter is what I've been looking for for YEARS! It gets rid of all the TV and computer birdies I have here (I live in a densly populated suburb where the average Yank would get the screaming abdabs from all those people around him). The next thing was to have a real test of what it can do, so I listened on 40m. As you'll know, 40m is QRM alley here in Europe....not any more! Of course it's not as good as filtering at IF, but what the hell - my IC706 can cope now, and so can my ears. The noise reduction is a blessing, but the brick-wall audio filters for SSB or CW are just bloody fantastic. I was able to copy weak CW signals that were buried in the crud. Then the REAL test: I hooked it up to my 80m DC receiver...erm.....is this my trusty old "Sudden"?? Once again.....AMAZING! If you want a new slogan: "Don't spend $$$$$$$$ on a new rig...get a DSP III and keep your wife happy too" ...this is one serious bit of equipment that everyone needs! 73, Pete PE1MHO/G7ECM

    Dave, My DSP-3 arrived as scheduled on 5 March. Just found the time to complete the project today. Every thing works GREAT!! Really enjoyed assembling this project. All parts were within specified tolerances and circuit board construction was fabulous. The instruction sheet was complete and easy to understand. I've been building and repairing ham gear and electronic devices/systems since 1964 and your DSP 3 qualifies as one of the best kits I have ever constructed. Thanks again for a quality product . 73's from foggybottom radio WB4PDY Larry M. Graham

    David, Kit went together in 2 nights, it works perfectly, construction was soo easy, its a great little unit only thing I did was bury the IC mounts under rubble and soldered the IC's straight to the board =0( , but it still works to spec regardless. It is a really nice quality product that works well at a great price. Everything was to what I expect from our suppliers and boardhouses where I work (quality).. Thanks again Dave, Sincerely, Collin A Dvorak K7AAB

    Hi Dave, I am really impressed with the performance of DSP III. Using a noise input and an audio spectrum analyser ( Freq51 software with a Sound Blaster 16 ) I checked each mode which were all as advertised. The SSTV mode does a great job on cleaning up a WEFAX signal from the Tokio Typhoon station JMH5 on 18.220 MHz, it cleaned out the low frequency noise and gave a much cleaner plot. 73 de N7IVM

    Dave, I finally found enough free time and put my DSP kit together. I've got to tell you, I'm impressed. All the parts were there. The circuit board is professionally made. The instructions were good. It all fits in the cabinet. The thing looks great. And, to top it off, it worked the first time I turned it on. I'm impressed! I'm still learning how to use the DSP. After 30 years of doing this kind of thing "by ear," it's going to take a while to get used to this new approach. I certainly have noticed how easily the DSP disposes of, lets say, tuners. 73... Peter, AE1T

    Dave, The box came today around lunchtime. I was all primed for it by downloading the manual earlier. Even with taking several breaks for meals nets, etc., the unit was assembled by 7 PM :>) What a great little unit! Beautiful engineering and quality parts. There were absolutely no difficulties encountered and it worked perfectly the minute I powered the DSP-3 on. I could copy signals on 160 meters that were virtually impossible; I found several stations that I could switch the unit in and out and verify the effectiveness. Congratulations, Dave, on a very worthwhile device (and you may quote me, HI). Don't forget to join us on 160 meters, Wednesday nights. 73, Troy, W6HV

    What are the differences between the DSP-1, DSP-2, and DSP-3? And, can I upgrade my DSP-1 or -2 to a DSP-3?

    The DSP-1 and its close cousin the DSP-2 unfortunately cannot be upgraded to the DSP-3. I made too many changes in both hardware and software. These changes were necessary to add additional capabilities to the DSP-3 design, which is substantially different from the earlier units.

    I changed the audio codec chip from an 8 bit unit to a 13 bit device, which adds another 30 dB of audio dynamic range. But, the 13 bit codec has serial I/O whereas the earlier 8 bit codec was parallel. Also, the 13 bit codec forces the sampling rate to be lower, which had major effects on the software. You get the idea - too many changes. (But, I suppose that is better than changing a resistor value and calling it a new model!)

    The differences between the DSP-2 and the DSP-3 are:

  • 1. 13 bit audio codec instead of 8 bits. This means a much wider dynamic range, which is especially important for CW where you may have a strong interfering station.
  • 2. Optional AGC in the LMS adaptive modes.
  • 3. Software AGC in the LMS adaptive modes, which means that the adaptive filters behave the same regardless of audio input level.
  • 4. SSTV filter
  • 5. European low tones RTTY/FSK filter
  • 6. DTMF decoder with memory
  • 7. CTCSS decoder with memory
  • 8. 1.8 kHz brick wall SSB filter
  • 9. 2.1 kHz brick wall SSB filter
  • 10. More CW filters
  • 11. CW filters can be tuned

  • Here's a picture of the new W9GR/N6SMF QTH (finally FINISHED!).

    From left to right: Dave Hershberger, W9GR; Sandy Hershberger, N6SMF, holding Percy, the cat; front row - Barkli, K9PUP, and Kiska, K9DOG. (Kiska is Barkli's aunt.)

    Ham Radio and Related Links

    American Radio Relay League
    Continental Electronics -- I am an engineer for Continental Electronics, where I do digital signal processing work and algorithm development.
    AXCERA -- I used to work for Axcera designing digital (HDTV/ATSC) broadcast transmitters, DSP modulators, adaptive equalization systems, etc. Some of my professional papers are on the Axcera site.
    High Sierra Antennas -- Mobile Antennas
    Dayton HamVention -- The Mother of All Hamfests - every year now in MAY!
    The Dilbert ZoneThe Dilbert Zone!
    Jim Hawkins' (WA2WHV) Radio Room -- See some really BIG transmitter installations; VOA, broadcast sites, etc.; LOTS of pictures!

  • Click to email me Mailbox You can reach Dave Hershberger, W9GR, by e-mail at: Click to email me