This uses a printed circuit board (PCB) to make building the circuit easy and reliable. It is modified from the original version to run off of 4xAAA batteries. It follows the LM386 version of the schematic from Techlib, with a few small modifications.
This device turns radio signals into audio - both intentional radio signals (like WiFi), and unintentional signals (like the hum from a switching power supply). It is a fun way to get some insight into the invisible world of radio.
Alligator clip wire (for testing the board before attaching the battery pack)
Download the gerbers zip file, and upload it to a PCB manufacturer. I use JLCPCB, which is fast and cheap. The default PCB options should be fine - feel free to change the color, if you like.
At time of writing, price to get 5 PCBs, including shipping to the US, was $19, with order-to-door time of about a week. You can use PCBShopper to look for a cheaper option, or share the boards among friends to bring down the unit cost!
The BOM csv file lists the components you'll need. You can upload this file to Digikey using their BOM support to automagically add the components to your cart. At time of writing the total cost of the components was about $15. If the battery holder is out of stock, you can substitute the similar part with a ribbon.
You'll also need to buy an antenna with a BNC connector. I used this one. Feel free to try different antennas - this isn't a precise device!