Schematic & Wiring Diagram

This simple circuit helps you sniff out RF radiation from your transmitter, improper joints, a broken wire or poor equipment with RF shielding. The tester is designed for the radio band amateur 2 meter (144-146 MHz in Europe). The instrument has a reading of 4-step LED and an audible alarm for high voltage radiation. The RF signal is received by an antenna and made to resonate by C1-L1. After rectification by the diode D1, the signal is fed to a two transistor Darlington amplifier HighGain, T2-T3. Assuming a 10-inch telescoping antenna using the RF level scale established for the LEDs is as follows:

When all the LEDs light, the (optional) UM66 sound / melody generator chip (IC1) also operates and provides an audible alarm. By changing the zener diode values ​​of D2, D4, D6 and D8, the step size and duration of the instrument may change as needed. To operate in other bands of ham or PMR, simply change the network-L1 C1 resonance.

For example, a transceiver 5 watt handheld equipped with a telescoping half-wave antenna (G = 3.5 dBd), there is an ERP (Effective Radiated Power) of just 10 watts and an emf of more than 8 volts near the head. Inductor L1 consists of 2.5 turns of 20 SWG (approximately 1 mm in diameter) enameled copper wire. The inner diameter is approximately 7 mm and no core is used.

Trimmer capacitor C1 associates is adjusted for the greatest number of LEDs to light at a relatively low fieldstrength position for a 2 m transceiver 145 MHz transmission. The tester is powered by a 9 V battery and consumes about 15 mA when all LEDs are on. Must be enclosed in a metal box.