The ADC and DAC are certainly adequate for audio so it will work. I've been interested in VHF and UHF high-speed modems so I have a starter kit outfitted with a high-speed ADC and DAC that plug into J3. So far I've tested the DDS and am in the middle of testing the second version of a 16-bit soft MCU. After that, I have a lot of Verilog code imported from a Spartan-3 project and converted from ISE 7 to ISE 10 that needs to be integrated and tested. That should eventualy result in an OFDM modem that operates at up to 2 Mbps. Real-time signal processing is done in dedicated modules for filtering, FFT and CORDIC, but in this design the soft processor is to handle everything between the FFT and the Ethernet port. Think of it as an Intersil HSP50214 plus an FFT and MCU in one FPGA.
The soft MCU would probably be enough to process 8 ksps audio for a modem as it has a MAC instruction. 3 or 4 would fit in an XC3S500E. 73, John KD6OZH ----- Original Message ----- From: Paul L Schmidt, K9PS To: digitalradio@yahoogroups.com Sent: Sunday, August 03, 2008 12:27 UTC Subject: Re: [digitalradio] Has anyone looked into FPGA-based digital modes? John B. Stephensen wrote: > FPGAs are useful for signal processing as you can do many operations in > parallel. FIR filter, FFT and CORDIC modules are available in the free > development software from Xilinx. They are very good for processing > wideband signals or digitizing an entire amateur band and then filtering > the result. Unfortunately, the starter kit has only low-speed > low-resolution ADCs and DACs. > > 73, > > John > KD6OZH Speed and resolution are, of course, relative :) While those chips are capable of crunching on half the HF spectrum at once, I was thinking initially of just audio (for which the on-board converters would be fine) - kind of a super-TNC, with capabilities (speed/bandwidth) similar to Pactor-III with no patents, open-source software, and significantly lower hardware costs. Sound card modes, of course, have gained popularity due to their flexibility and low cost - but can't handle the tight timing needed for pactor-type modes. It just seemed to me that something like a commercially-available low-cost FPGA board might be able to get the best of both worlds. Yeah, I'm suggesting a minor paradigm shift. Scary. 73, Paul / K9PS
