VOA Radiogram listeners often see something like this on their Fldigi software display ….

The actual MFSK32 audio is the trace above and below 1500 Hz. The trace to the right, which actually extends to 3500 Hz, is the second audio harmonic.

I think these harmonics also exist with voice and music programming, but because the audio is so diffused, they are usually not noticed. With MFSK32 and other digital modes, however, the audio is so precisely defined that the harmonic is more noticeable.

VOA Radiogram listener Merkouris in Greece tried an experiment with the second audio harmonic.  He wrote:

Last weekend I tuned on the VOA radiogram frequency in AM mode, although I usually set my receiver in SSB mode. As the 2nd harmonic was clearly visible on the fldigi waterfall, I decided to give it a try to decode it.

Using Audacity, I changed the pitch of the recorded audio to -50%, then I cropped the audio frequencies below 1200 Hz. The results of the decode were about 50% copy of the text in MFSK32 and 99% copy of the text in MFSK16. Regarding the images, only two out of the transmitted five were decoded with quite interesting outputs.

Here follow the pictures, compared to the images that were decoded from the 1st harmonic.

The picture is of Ajit Pai, chairman of the Federal Communications Commission, broadcast on VOA Radiogram the weekend of  13-14 May 2017.