Was helping someone make a DIY field detector coil for HF with just an LED and some wire. Thought I would repost here:
- Figure out roughly what dimensions you want the inductor to be (circles are easiest but some similar coil shapes couple better)
- grab some enamel coated magnet wire (maybe 0.32mm diameter) and some pico farad capacitors (or LEDs which are about 20pF)
- Use an LC tank circuit calculator like this one:
https://goodcalculators.com/resonant-frequency-calculator/
plug in 13.56MHz as the frequency and some capacitor values that you have handy (more capacitance means wider frequency range while more inductance means better coupling). Figure out a rough inductance that matches with your available capacitors (ex: 47pF capacitor + 2.93uH inductor) - Once you have a target inductance use an inductor calculator like this one
Coil Inductance Calculator
If you want a flat coil change it to Multi-layer, single-row coil and Centimeters. Try out some values until you find a size/turns that matches your target inductance - take your enamel wire and cut more than you would need to wind the coil (you can calculate the linear length easily enough from the circumference). Wind the coil. You can wind it on some tape for stability or add cyanoacrylate glue afterwards to bind the windings together. Don’t use metal tools or you’ll scrape off the enamel which can cause a short
- use a soldering iron to burn off the enamel from the wire tips. Tin the iron tip, press it to the wire, add more solder until the bead engulfs the wire, then slowly move it along the wire to clean it.
- solder an appropriate capacitor (or LED) to the wire tips
