I recently built a simple AM receiver for listening to shortwave radio. The circuit uses just 4 transistors in total, can be built on a breadboard and works pretty well despite it’s simplicity. It works as a regenerative receiver, which means that some of the amplified RF is fed back to the input. This greatly increases sensitivity and selectivity at the cost of having an extra potentiometer that has to be tuned, since too much feedback will cause oscillation. Another downside is that the selectivity is still not great enough to properly separate stations on crowded bands in the evening.
The point of this project is having a receiver that can be thrown together in a pinch while still working well, so some parts such as the AF amplifier are rather primitive on purpose. The circuit draws around 0.5 Watts, which can be reduced substantially if the speaker is swapped for headphones. It should be noted that the demodulation J-FET Q3 could be replaced by a Schottky diode, but i did not have any at hand.
It can only demodulate AM, not FM or SSB. I’m using around 3 meters of wire as the antenna, while the other side of the resonance circuit is grounded through my heating system. After dusk, i can pick up many international stations such as Radio Romania International or Radio China International here in western Germany. With the given component values the receiver should work between ~3 to ~7.5 MHz
Below is a schematic, have fun building the receiver and SWLing!