Motorola DSP Receiver

Ralph Stirling, KC3F, and I built the first generation using a Texas Instruments C5X DSK digital signal processing starter kit. Let it suffice to say that the second generation is a tremendous improvement over the first, because it uses a much more suitable DSP evaluation board from Motorola, the DSP56002EVM. You may wonder what the big deal is. Why are so many of the latest radios coming with DSP

demodulators and filters Digital techniques have several advantages. Probably the most exciting is that everything is done in software. That means when I design a new demodulator you can download it to your radio and then you have my new demodulator. No soldering; no hunting parts; no ugly modifications; it`s so easy! Another benefit is that results are predictable. Component tolerances are not a factor as they are with analog signal processing. Simulations are easier to do and their results more closely approximate what happens in the actual system. Yet another advantage results from the speed of today`s DSPs. Nowadays it is quite realistic to have a digital filter with the equivalent of hundreds of poles, a filter that would require hundreds of inductors, capacitors or crystals in the analog world. Few analog designers use more than ten poles in a filter, because it`s very difficult to make designs with more work properly. This project actually started back in 1994. Ralph Stirling, KC3F, and I did exactly what Rick Campbell, KK7B, suggested in his original article on the R2 receiver. We used Rick`s R2 receiver and the Texas Instruments C5X DSK digital signal processing starter kit to construct a DSP based direct conversion receiver. We modified the DSK with our custom daughter board containing another TLC32040 codec. The DSP replaced the analog phase shift network with its digital counterpart and a sharp digital filter....

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