This is a broad band field sensing probe that has about 15cm length antenna. It is capable to detect radio energy and drive millivolt level signals to the input of digital volt meter.

This circuit was used to test 4MHz, 35 MHz, 55 MHz, 100 MHz, 384 MHz, 900 MHz, a cell phone, and a microwave oven. Indicator worked well with all mentioned sources. Indicator is powered from single 1.5V AA cell where current drain is about 60uA. Circuit can be powered with higher voltages in order to increase it’s sensitivity. [link]

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