hobby #227

Heterodyne Bat Detecting and Call Identification

Building and field-using a heterodyne ultrasonic detector to eavesdrop on bat echolocation at dusk — tuning a local oscillator to mix the bats' 20–120 kHz calls down into the audible range, then identifying species by the rhythm, peak frequency, and 'feeding buzz' of the down-converted clicks while logging passes along a river-valley transect.

I Could See Them Hunting but Heard Only One

I built a detector to hear bats hunting over the river, then stood there deaf while five of them fed above my head. The tuning knob wasn't the problem. The part I never questioned was.

code-a-day tied to this hobby

One Bin at a Time: The Goertzel Resonator Goertzel algorithm

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