rf detector for 2m circuit schematic

Simple 144 MHz RF Detector

This simple circuit helps you sniff out RF radiation leaking from your transmitter, improper joints, a broken cable or equipment with poor RF shielding. The tester is designed for the 2-m amateur radio band (144-146 MHz in Europe). The instrument has a 4-step LED readout and an audible alarm for high radiation voltages. The RF signal is picked up by an antenna and made to resonate by C1-L1. After rectifying by diode D1, the signal is fed to a two-transistor highgain Darlington amplifier, T2-T3.

Assuming that a 10-inch telescopic antenna is used, the RF level scale set up for the LEDs is as follows:

When all LEDs light, the (optional) UM66 sound/melody generator chip (IC1) is also actuated and supplies an audible alarm. By changing the values of zener diodes D2, D4, D6 and D8, the step size and span of the instrument may be changed as required. For operation in other ham or PMR bands, simply change the resonant network C1-L1.

As an example, a 5-watt handheld transceiver fitted with a half-wave telescopic antenna (G = 3.5 dBd), will produce an ERP (effective radiated power) of almost 10 watts and an e.m.f. of more than 8 volts close to your head. Inductor L1 consists of 2.5 turns of 20 SWG (approx. 1 mm dia) enamelled copper wire. The inside diameter is about 7 mm and no core is used.

The associated trimmer capacitor C1 is tuned for the highest number of LEDs to light at a relatively low fieldstrength put up by a 2-m transceiver transmitting at 145 MHz.
The tester is powered by a 9-V battery and draws about 15 mA when all LEDs are on. It should be enclosed in a metal case.

144 MHz rf detector circuit schematic

rf detector for 2m circuit schematic


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  • AstroCircuit


    Just wondering if this circuit ended up working well, or not?

    How might you suggest altering the L1-C1 section for, say, 150-153MHz band, or even higher frequency to 322MHz? Would the circuit still work?

    Also, you mention that the step size and span of the instrument can be altered by changing the Zener Diodes D2-8… What do you mean by this? Will increasing their value simply increase the step size?

    Thank you so much in advance for the help – as you can probably tell, I’m just a basic-knowledge hobbyist at the moment, and need all the instruction I can get! Haha!

    Kindest regards,

    Dr Karlette

  • Dimeji

    I’m highly interested in this project.pls can you forward the details,amount and timeline of this project.

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