We found this circuit in an Australian documentation from 1991. The circuit is suitable for SMD mounting thus making it very small. The circuit was sold in a kit at the time.
This circuit is from a 2004 documentation serving for signals from 1 MHz to 160 MHz. The antenna is...
This filter of two transistors has the cutoff frequency determined by the formulas next to the...
This Philips commercial circuit is from the 90's documentation. The integrated circuit must be...