This is a PCB for the audio amplifier IC version of the Techlib Amazing All-Band Receiver. It is a device that makes the normally-invisible world of RF audible.
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The latest and greatest version is in low-voltage. This version is powered by 4xAAA, and is relatively simple. This is the one you want to build.
all-through-hole and audio-rf contain the previous (overengineered) version, which was powered by a single 18650 lithium-ion battery. It used a boost converter followed by a linear regulator to step the battery voltage up to 9v. This is overkill, and also caused noise issues.