Rev 1.3 frontend sensitivity: finding and evidence - #12
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The rev 1.3 receiver was about 3 dB less sensitive than a Mode-S Beast on the same conducted stimulus. The cause was the preamble detector's absolute power threshold and 32 us holdoff, not the RF frontend. power_threshold 700 with an 8 us holdoff brings the conducted knee to within 0.5 dB of the Beast. On air, median max range per bearing rose from 76 km to 164 km, roughly level with a Radarcape that used the same site. Includes the curated sweep, counter and coverage data, the plots, the analysis scripts, and a short record of what was ruled out. Coverage data is reduced to bearing, range and altitude; no site or aircraft coordinates are included. Raw captures are not committed. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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planewatcher/analysis/frontend-sensitivity-2026-09/: the outcome of the rev 1.3 frontend sensitivity investigation, with its evidence.Finding. The rev 1.3 receiver was about 3 dB less sensitive than a Mode-S Beast on the same conducted stimulus. The RF frontend was not the cause: raw ADC samples still carried decodable frames past the knee. The preamble detector's absolute power threshold (2000 at 32 MS/s) rejected them, and its 32 µs holdoff let false triggers blank real frames.
Fix (software repo,
f842867).power_threshold700 and holdoff 8 µs as bitstream defaults. Conducted knee within 0.5 dB of the Beast, with no noise triggers on a terminated input. On air, median max range per bearing rose from 76 km to 164 km, roughly level with a Radarcape that used the same site and antenna.Ruled out:
Contents:
README.md: the write-up.data/: curated sweep, counter and coverage data.plots/: regenerable withscripts/make_plots.py.scripts/: the analysis tools.Coverage data is reduced to bearing, range and altitude; no site or aircraft coordinates are included. Raw captures are not committed.
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