need advice for budget friendly road to FPGA based soft(firm)ware defined radio


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I'm looking for an inexpensive (<= $200) platform to play with software (or rather firmware) defined radio. Looking at Zygotes list of EVM's, Linear Technologies makes an ADC/DAC combo EVM that interfaces well with FPGA boards but $300 + at least $100 for the FPGA board is too much. I just need a few MHz sampling rate (but obviously the more the better.) Boards with ADC's onboard are easy to come by, but I dont see many with DACs. I can handle the up/down converter with junk box parts. Any advice?

Thanks

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This is probably not what you want to hear but there are quite a few reasons why I'd do software-defined "radio" for educational purposes at audio frequency with a sound card, e.g. in a 1 kHz band.

Approached in an efficient way, "Software"-defined radio work is done mostly in software, with hardware for validation to pinpoint the bugs. And FPGA is not as cool as it seems when I should more or less know exactly what I want before writing the first line of code (unless you treat it as a flexible generic R&D platform in which case you may need10+ times the FPGA size of a "proper" FPGA implementation. Which is not compatible with "budget friendly"). Matlab (free Octave) is the tool of choice for SDR.

The fundamentals (synchronization, carrier frequency offset estimation and correction, phase tracking , channel estimation and equalization, added noise / phase noise / intermodulation distortion etc etc) are very similar for sound waves but I won't be stumbling in the dark trying to do debugging that would involve five-plus digit range equipment in a professional environment.

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@apchar,

I recently had an opportunity to do some gateway defined radio work with an iCE40 Ultra 5LP, a digilent MIC3 MEMS microphone PMod, and a SX1257-Pmod for a radio.  Hardware wise, the set up was really easy to do--and so I'd recommend it to you at all if you are interested.

You can find my project, source code and references to hardware, here.

Dan

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On 2/15/2020 at 4:46 PM, apchar said:

I'm looking for an inexpensive (<= $200) platform to play with software (or rather firmware) defined radio.

Normally, I'd say that this depends on what you what you want to play with, but your budget will limit this to canned modules that already implement the fun stuff. I've posted a CMOD/ESP8266 project in the Project vault that might set on in the right direction. The ESP32 might be a better option. All you need is a good HDL SPI interface. These devices have very good software support and modules for any budget are available.

If what you want to do is play with the nuts and bolts of radio then I have to agree with the suggestion provided by xc6lx45 that a sound card or perhaps motherboard audio circuitry is the cheapest way to go. There are FPGA boards with an audio CODEC in your budget but doing this in an HDL is not for the weak of heart or newbie. There just isn't much available for under about $500 in the FPGA world involving ADC/DAC hardware. I'd point you toward Terasic to see the best options. Look for the cheapest FPGA board with an HSMC connector; but their converter boards are just above your budget limit.

Edited by zygot
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