This circuit for the 3 to 6 MHz band was found in a 90s Popular Electronics. The components of the network formed by C6 depend on the frequency range to be covered.
This 1967 Philips circuit recognizes a light signal (visible or infrared) modulated by tone. The...
This circuit turns on an old cassette recorder when the telephone rings, thus enabling the...
This is the receiver for the previous circuit transmitter. Similarly, no information about the...