An RF field detector circuit that can be used in measurement and verification stage power antennas and transmitters can be designed using some transistors and common electronic components.

This RF field detector circuit is designed with a radio frequency transistor type MOS-FET with two gates. Gain factor is set by the potentiometer P1. S2 switch allows selecting one of three ranges: 480 kHz ... 2.4 MHz (L1), 2.4 ... 12 MHz (L2) and 12 ... 40 MHz (L3).

A telescopic antenna with a length of 30 cm is sufficient for the antenna.