This circuit implements two logic functions at the same time. The diodes are for general use and the resistors have typical values of 2k2 for logic of 5 V.
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...