The circuit behaves like a true mosquito: once the light dims, the mosquito starts an annoying buzz. When its light again it becomes mute, so that, as in the case of genuine mosquito is very difficult to spot.

This Ultrasonic Sensor Circuit consists of a set of ultrasonic receiver and transmitter which operate at the same frequency. When something moves in the area covered the circuit’s fine balance is disturbed and the alarm is triggered. The ultrasonic circuit is very sensitive and can be adjusted to reset itself automatically or to stay triggered till it is reset manually after an alarm.

This 2 meter 144 MHz fox hunt transmitter is used in amateur competitions where a hidden transmitter is to be “hunted” using mostly homebrewed receivers and antennas. The foxhunt electronic circuit is the transmitter. It radiates a high quality signal without unwanted harmonics. Transistor T1 and the crystal togheter make the oscillator that generates a 36MHz signal.

The transmitter on 2 meters 144 MHz was designed mainly for use by radio amateurs as radio beacon and to this end, it produces a signal of good quality and without unwanted harmonics. T1 transistor, in association with cristall X1, works as oscillator on 36 MHz. L1-C3 filter eliminates any tendency of the circuit oscillation on 12MHz (fundamental frequency of the crystal).