The image depicts a “Simple RF Indicator,” a passive device for detecting radio frequency (RF) signals in coaxial cables. It’s a clever hack using basic components: a coaxial connector, toroid core, 7-9 turns of blue wire, and a red LED.
How It Works
RF current flows through the coax (single-turn primary), inducing voltage in the wire coil (secondary) via the toroid’s magnetic field. This voltage lights the LED, indicating RF presence. Brightness correlates with power level. Based on Faraday’s law, it’s a mini current transformer—sensitive to HF/VHF frequencies (1-150 MHz). The ferrite core enhances efficiency, concentrating flux for better sensitivity without external power.
Building It
Materials: Ferrite toroid ($1-2), magnet wire, LED, coax stub. Wind turns on toroid over coax, connect LED. Test with low-power transmitter (1-5W). Cost: Under $10. Ideal for hams verifying output or tuning antennas. For best results, use enameled wire to prevent shorts, and experiment with turn counts—fewer for higher frequencies to avoid resonance issues.
Applications & Limits
Use for transmitter checks, leak detection, or education. In field operations, it helps spot intermittent signals during portable setups. Limitations: Needs ~1W minimum, no quantification, frequency-specific. Variations include adding a diode for rectification or multiple LEDs for stepped indication. Modern twists: Integrate with Arduino for digital readout, blending analog simplicity with IoT smarts.
This minimalist tool Simple RF Indicator proves RF detection doesn’t require fancy gear—perfect for makers and experimenters exploring electromagnetics on a budget!
This design is credited to DU1RZ and featured on the Philippine Amateur Radio Association (PARA) website in their multiband wire beam antenna project.
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