This circuit responds to RF
signals from below the standard broadcast band to well over 500 MHz, and provides a visual
and audible indication when a signal is received. The circuit is designed to receive
low-powered signals as well as strong sources of energy by adjusting the bias on the
pick-up diode, D1, with R2. A very sensitive setting can be obtained by carefully
adjusting R2 until the LED just begins to light and a faint sound is produced by the Piezo
sounder. |