We find this encoding circuit in an American 1980s amateur radio documentation. The circuit can be implemented with equivalent modern components.
The dsPIC33EP128GS808 Digital Signal Controller Family now Offers up to 128 KB of Flash while...
This circuit can be used with motors or resistive loads, such as heaters and incandescent lamps....
This receiver of two transistors for the 3.5 MHz band was found in a circuit manual from the 80's....