Thread

A software thing I built: GPS on a 25MHz 486-SX

75 points · 24 comments · JPLeRouzic

guenthert · 1789545640 · focus · HN ↗
"real-time GPS-driven moving map display"
Not the IMHO more interesting analog tech which lifts signals out of thermal noise.
1. JPLeRouzic · 1789558778 · focus · HN ↗
  That looks interesting, what technology "lifts signals out of thermal noise"?
  1. FrankPetrilli · 1789561090 · focus · HN ↗
    GPS - look into Gold Codes [1] and auto-correlation. GPS arrives on your device at -128dBm, give or take, while thermal noise is -111dBm at the ~2MHz sampling bandwidth used. We use the processing gain from correlating against the ~1Mchip/s gold code to extract the lower bitrate signal, so you're pulling signals from approximately 20dB below the relevant thermal noise floor.
    [1] <a href="https://en.wikipedia.org/wiki/Gold_code" rel="nofollow">https://en.wikipedia.org/wiki/Gold_code

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