Concept Session 6 - SDR Design

The next step in building the complete Concept Arduino based SDR receiver is to study and understand the design of the SDR shield. And to install the HDSDR software on your PC and to check the sound card capability of your PC, ready for testing the completed project.



An outline of the SDR shield is:



A good sound card is required for SDR operation. A microphone input level input should feed a A-to-D convertor, preferably running at a 96kHz data rate. This will give a thing range on screen of +/- 48kHz. A data rate of 48kHz is acceptable, but will reduce the tuning range to +/-24kHz. If your PC does not have a suitable sound input or A-to-D convertor then an external one can be used. I recommend the StarTech ICUSBAUDIO2D (search on Amazon) which provides input and output at 96kHz.



The basic configuration of an SDR set-up is



The 3 board Arduino stack - Arduino Uno + VFO + SDR - has two audio outputs that feed the A-to-D convertor. This in turn feeds the signals to the PC HDSDR software (or the DSP Radio software on a Mac). This illustrates the installation of the HDSDR software from www.hdsdr.de or the DSP Radio software from DL2SDR



The HDSDR program looks like this when in operation:



SDR shield design

The complete schematic of the SDR shield is shown below. The circuit is made up of three parts, an input BPF, the Baseband filter CMOS switch and the audio output amplifiers.



In detail:







The Baseband filter is fed with I & Q quadrature signals from the Johnson counter on the VFO shield, These commutate the switch through four positions and switch the incoming RF in four quadrants onto output capacitors, and on to the audio amplifies.





In order to connect the SDR to the PC or A-to-D convertor a short cable is needed:



And before the build, covered in the next posting, two toroid should be wound:



Now you are ready to build and use the SDR receiver.