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Posted Friday, May 14, 2010 3:45 PM
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It is apparent that requiring Windows-based personal computers to perform the SDR functions is sometimes problematic -- PowerSDR freezing up, device driver conflicts, etc. Windows is just too busy to guarantee time-locked performance of sub-threads.

I would like to apply my vast experience with direct DSP programming to the problem, moving the most time-critical functions into a dedicated DSP (one or more), and having the PC just perform GUI display and user interactions.

The high-end guys, like Pentek et al, use embedded processors running hard-real-time OS's (VRTX, VxWorks, etc). But they need to support all kinds of advanced military-grade communication schemes. I don't think we need such elaborate support for a simple Ham radio SDR. A single DSP ought to be able to handle just about everything I have seen in the PowerSDR code.

Even something like an old SHARC or MC56309 should be able to handle these chores. We do it all the time in the audio engineering realm. And with a more modern DSP at hand, we could even push the limits to 192 kHz, 384 kHz, or higher. One application, for our professional work, requires a bandwidth of no less than 6 MHz for the ATSC-M/H protocol on digital TV.

The objection has been raised that moving the SDR code into a dedicated processor obviates the spectrum and waterfall displays, but I don't believe that. It is very simple to have a DSP generate buffers of data that can be transferred to an external control program. These buffers update at no more than 30 Hz for visual displays, which is very slow compared to SDR processing requirements. Same thing holds for user control of various functions. Simple fast-interrupt handlers in the DSP can easily accept and modify internal working variables of the DSP code. I have done this many many times in other projects.

Right now the FlexRadios must have some minimal processor running the FireWire interface, decoding the MIDI control messages, and running I/O buffers. It would be nice to see a schematic of the innards of the Flex-3000 to allow for user customization and modifications.

73 de N7AIG
Post #2658
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