read AM signal only with an Arduino Some people have managed to send simple AM signals with just a bare Arduino. An example is here.
This works thanks to the fact that the PWM can reach high frequencies and, setting the divider properly, it is possible to broadcast a 1337 kHz carrier over a short distance with just a wire acting as an antenna.
I know it's not that useful, but it's really nice as an educational tool.

I was wondering if it would be possible to apply the same concept, but for the receiver. For instance simply using a pulseIn() detection on a pin connected to an antenna. Would it be possible to detect the carrier, and, maybe, even demodulate a message, eg, in morse code?

If not, would just a adding an amplifier be sufficient? Any recommendations for the amplfier and the circuit?

Thanks very much for your suggestions.
AM (Amplitude Modulation) varies the amplitude of the carrier based on the input signal. So, assuming you had some circuitry (LC circuit) to receive a particular carrier frequency and managed to boost the voltage so that it was in the range 0-5v then you would able to feed this to an analog input on the Arduino.

AnalogRead requires around 100uS per sample, so your max sampling rate would be 10K/s, which might just cut it for voice (up to 3.4Khz, sampling at least 2 * the highest freq).

However, you then need to do something with the sample value (in code) and depending on how long that 'something' takes, your actual sample rate will be reduced.