Ultrasonic remote control transmitter (CB8397E)

Found in a 90s Popular Electronics, this circuit excites a 40 kHz ultrasonic transducer. The transistor can be a BD135 or other medium power.

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5 MHz oscillator with 250 kHz variation (CB13852E)
We found this oscillator in a documentation for radio amateurs from the 1970s. The circuit can use...
Impedance Matcher (CB15540E)
Many oscilloscopes have high impedance inputs that make it difficult to observe high frequency signals...
Optical Communicator – Receiver (CB25536E)
This is the receiver for the previous circuit we found in the December 1992 Radio Electronics...