This circuit was found in a British documentation from 1969. It can be implemented with modern transistors. The pass band is 6 MHz.
This circuit is intended for recording conversations by amateur radio, being activated by the...
This simulation shows how to use an operational amplifier as a voltage comparator. The sample uses the...
circuit is used to increase the sensivity of a relay. A 50 to 100 mA relay can be triggered with...