Homemade 6 GHz pulse compression radar

Original Article ↗ Hacker News Discussion ↗

Overall reaction

  • Strong enthusiasm for the technical depth: RF, high‑speed digital, FPGA, and signal processing all in one project.
  • Several readers call it unusually sophisticated for a single hobbyist and compare it favorably to professional radar work.
  • Some note the relatively low out‑of‑pocket cost (~$570 including VAT and shipping) versus the enormous time and expertise implied.

Cost, tools, and test equipment

  • Itemized cost from the author: ~$330 for PCB fab/assembly of two boards, ~$240 for components.
  • Readers assume expensive RF test gear is required; author reports using only an oscilloscope, multimeter, and open‑source tools.
  • This prompts discussion that a lot of GHz‑class hobby RF is now being done with modest equipment, although others emphasize that debugging without analyzers can be hard.

PCB design and high‑speed layout

  • Multiple questions on layer stack: why ground planes on inner layers, why not top/bottom.
  • Explanations: components need very short ground access; continuous planes on inner layers give controlled impedance for high‑speed traces on outer layers.
  • Discussion of DDR3 length‑matching: “squiggly” routes are to match delays within ~±10 ps; internal FPGA package delays can be exported and manually compensated in layout.
  • Some note that FPGAs can correct timing in logic, but less so for hard IP like DDR controllers.

Applications and extensions (phased arrays, automotive, SAR)

  • Curiosity about adapting such radar to 3D voxel mapping or LiDAR‑like use; replies say this needs large MIMO arrays (hundreds–thousands of channels) and heavy processing.
  • Automotive 4D radars at ~80 GHz with compact phased arrays are cited as an existence proof and potential LiDAR competitor.
  • Some want follow‑on projects: phased arrays, synthetic aperture radar, rotating/tilting mounts for volumetric mapping.

Legal, safety, and ITAR concerns

  • Discussion of 6 GHz rules in the US: unlicensed, but with very low allowed EIRP; the demonstrated 1 W PA plus high‑gain antenna would exceed that.
  • Consensus that regulators (e.g., spectrum authorities) would react before the military, though military aircraft may still see unknown radar emissions on warning systems.
  • Multiple references to ITAR: passive radar code removed from some open projects; sharing restricted code may be a crime; others complain ITAR blocks useful civilian tech (e.g., advanced GPS antennas).
  • RF safety: generally considered similar to Wi‑Fi/cellular (non‑ionizing), but high power can heat tissue; anecdotes about radar overexposure and debate about cancer risk vs pure thermal effects.

Miscellaneous

  • Side discussions on cheap doppler and presence‑sensor radars, ultra‑cheap repurposed “PIR” radar chips, and the reliability and sourcing (including scrap) of low‑cost Chinese electronics and FPGAs.