Field Strength Indicator Without Microcontroller

The project is a non-microcontroller version of RF Field Strength Probe using Atmel AVR microcontroller AT90S1200.

From the microcontroller based version, the broad band probe has a small antenna consisting of insulated wire. The radio frequency energy coupled to the antenna is detected and made available to drive millivolt level signals to the input of a digital voltmeter. For convenience, it was battery-powered with very low current drain and automatic shutdown for long battery life.
Multiple purposes are being served by the hot melt glue that covers the circuit which includes aiding to keep the temperature even among the three transistors to minimize thermal drift. It also protects the components from physical damage and it holds the battery holder on the board.

The circuit is being powered by a single 1.5V AA cell where the current drain is so small amounting to about 60mA. The supply voltage can be increased up to the breakdown voltage of the transistors to increase the sensitivity although the thermal drift sensitivity will be increased as well. The RF voltage coupled by the antenna is applied to the base of one transistor causing increase in transistor collector current.

Rest of the project