This circuit was found in documentation from the 1970s. However, it can be implemented with modern transistors such as 2N2222 for Q1 and BF494 for Q2. The crystal depends on the desired frequency.
The coil of this receiver determines the range. It can have 2 to 10 turns of wire 20 to 24 in the...
This circuit has tone control, and its power depends on the supply voltage. The circuit is from...
This circuit with 10 MHz and 1.25 MHz TTL outputs was found in an American documentation from the...