Detecting RF Radiation: Basic Circuit
This uncomplicated circuit serves as a tool to identify RF radiation leaks stemming from your transmitter, faulty connections, damaged cables, or devices lacking proper RF shielding. Specifically designed for the 2-meter amateur radio band (144–146 MHz in Europe), the tester features a 4-step LED display and emits an audible alarm for elevated radiation voltages.
Antenna Reception and Resonance
The RF signal is captured through an antenna and induced to resonate with the help of components C1 and L1. Following rectification by diode D1, the signal is directed to a high-gain Darlington amplifier comprising two transistors, T2 and T3.
RF Level Scale Calibration
Assuming a 10-inch telescopic antenna is employed, the RF signal strength level used to calibrate the LEDs is determined as follows:
Audible Alarm Activation and Customization
When all LEDs illuminate, the optional UM66 sound/melody generator chip (IC1) is activated, triggering an audible alarm. Altering the values of Zener diodes D2, D4, D6, and D8 allows for customization of the instrument’s step size and span. To operate in different ham or PMR bands, simply modify the resonant network C1-L1. For instance, a 5-watt handheld transceiver equipped with a half-wave telescopic antenna (G = 3.5 dBd) can generate an ERP (effective radiated power) of nearly 10 watts and an e.m.f. of over 8 volts close to your head. Inductor L1, made of 2.5 turns of 20 SWG (approximately 1 mm dia) enameled copper wire with an inside diameter of about 7 mm, does not require a core.
Tuning and Power Requirements
The associated trimmer capacitor C1 is adjusted for the maximum number of LEDs to light at a relatively low field strength produced by a 2-meter transceiver operating at 145 MHz. The tester operates on a 9-V battery, drawing approximately 15 mA when all LEDs are active. It is recommended to enclose the tester in a metal case for optimal performance.
Understanding RF Electromagnetic Radiation
Radiofrequency (RF) electromagnetic radiation (EMR) entail the transfer of energy through radio waves. RF EMR falls within the frequency range from 100 kilohertz (kHz) to 300 gigahertz (GHz). Notably, RF EMR is classified as non-ionizing radiation. Indicating that it lacks the energy required to break chemical bonds or remove electrons (ionization).