This circuit can generate signals in the VHF range and can be used as the basis for small transmitters. The frequency depends on the coil, which can have 2 to 8 turns for the range of 50 to 200 MHz.
This circuit is from an American documentation about filters. The operational amplifiers are 741...
This circuit allows linear brightness control of an LED from an input voltage. The power supply must...
I found this circuit in a 2005 Wireless World and it is ideal for driving high power white LEDs....