Anyone who designs, builds, or repairs radio receivers can make good use of a small AM signal generator. With a suitable signal waveform, you don’t even need to be able to adjust the frequency. This works if the generator operates at an adequately low frequency and generates enough harmonics. The ATtiny13 AM signal generator described here produces short pulses at a rate of 70◦kHz. This results in strong harmonics covering the entire long-wave (LW) and medium-wave (MW) radio spectrum. The pulse train is also briefly interrupted at regular intervals to produce amplitude modulation (AM) at a frequency of 750◦Hz. A radio can therefore receive an AM test signal at 70◦kHz, 140◦kHz, 210◦kHz, etc. and demodulate it to produce an audible tone.