This electronic rf detector circuit diagram is based on common transistors and other few common components . This rf detector responds to RF signals bellow the standard broadcast band to well over 500 MHz and provides an visual , and audible indication when the signal is received . By adjusting the bias of D2 with the R2 potentiometer the circuit can detect low power or strong signals . A very sensitive setting can be obtained by modifying the R2 until the LED begins to light .
As you can see in this rf detector circuit diagram , the indications is given by a piezo buzzer an a LED .
The circuit can be powered using a simple 9 volts battery or any other 9 volts DC power supply circuit . If the rf detector is not enough sensitive you can connect a good wideband RF amp between the antenna and the detector diode .
Keep diode and capacitor (C1) leads short to minimize stray inductance. The used transistors can be : 2N3906 ,2N2907 or other PNP high gain transistor for Q2 and PN2222A , 2N3904 or other NPN high gain transistor for Q1 .