Found in an old Xicor documentation, this circuit makes use of an X9241, which contains four digitally controlled analog potentiometers.
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...