DC Rig prepares for DSP era
OH2NLT 16.09.2004
About one week ago I restarted my DSP learning project, which was left dormant last spring. I have to admit I am in the very beginning at the learning curve. Good goal for my first real exercise was to replace our DC receiver band pass filter with DSP filter. Test platform hardware is our DC transceiver and Analog Devices
BF533 kit. BF533 is not the best DSP for serious audio filters because of it is 16bit machine. With 16bits you can get only about 96db numeric dynamic range. Anyway BF533 kit provides good test and learning platform. Today I held first QSO with my DSP filters.
I have implemented few different test filters into my program. Filters can be changed on fly with push buttons at low right corner. LED indicators show which filter is in use if you do not hear it!
Codec inputs and outputs are for 1Vrms level. Adapter was build from analog filter board. Receiver full dynamic range is not available with this setup. Something quickly just for filter tests.
DSP FIR filter in fact looks like this.
Calculating coefficients for test filter.
This is not an example how things should be done. This is my first DSP program. I had difficulties to understand how VisualDSP library FIR function operates. I also contacted manufacturers support. Only help I got there was instructions "how to check dip switches on the development board". After several nights research I got things working. Next catch was 1.15 fractional constants. You can not write constant as 0.999 you have to declare it in hex format.
