Sonar, in plain English

Lower kHz pings reach deeper but lose detail. Higher kHz pings paint sharper images but die out shallow.

Rule of thumb: 50–83 kHz for deep, 200 kHz for everyday, 455–800 kHz for structure scanning.

Each frequency emits a cone-shaped beam under the boat. Wider cones cover more bottom, narrower cones see more detail.

bottom_diameter = 2 · depth · tan(cone / 2)

Instead of pinging at a single frequency, CHIRP sweeps a band (e.g. 80–160 kHz). The receiver compresses the return for sharper edges and better target separation. CHIRP is why two fish 6 inches apart can show as two arches instead of one blob.

Amplifies returns. Crank it and you see weak fish — and a screen full of speckle. Drop it and you see only strong returns. Sweet spot: just below where the screen gets noisy.

Very high frequency (455/800 kHz) painted as a photo-like image. Brilliant for trees, brush, rocks, and structure ID. Loses depth — useless past ~25 m.

As the boat moves, a fish enters one side of the cone, passes through the center (closest to the transducer), and exits the other side. The distance from transducer changes — short, then shorter, then longer — drawing an arch. Stationary fish make dots; off-center fish make half-arches.