23 lines
1.5 KiB
Markdown
23 lines
1.5 KiB
Markdown
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# FAQ
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### Can I buy one?
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No, not at the moment. So far this is just a private hobby project.
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### Can I build one?
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Absolutely. All required files are available and if you are not afraid to solder a lot of small components you can certainly build your own. The total BOM cost (without the aluminium shielding) is about 200€ when only buying parts for one PCB.
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There are some [basic instructions](DeveloperInfo/BuildAndFlash.md) to help get started on the software side.
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### Why is the final IF so high?
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I am using 250kHz as the final IF frequency. Compared to some other VNA projects this is rather high and requires a fast (more expensive) ADC. However, it also makes the sweep rate faster: each measurement point takes at least one IF period (more if noise should be reduced to practical levels).
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### Why the FPGA?
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Why not sample the ADCs directly with (a more powerful) STM32? Or even use the ADC on the µC itself?
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* I wanted more than the 12bits provided with by internal STM32 ADCs (and also better SNR)
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* Sampling the three 16bit 1MSamples/s ADCs with an STM might be possible but certainly would be a challenge
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* More flexibility with the FPGA controlling all critical RF components (e.g. setting up all PLLs concurrently for each measurement point, further increasing sweep rate)
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* Enough power for future features (e.g. spectrum analyzer mode with FFT)
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### If there has to be an FPGA, why one with a closed-source toolchain?
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* Sorry, thats just what I had experience with (also, the toolchain is free, just not open-source)
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