In which military band would a short wave radio signal at 20 MHz exist?

A short wave radio signal operating at 20 MHz falls within the range typically classified as the A-band. The A-band is generally recognized to encompass frequencies from about 10 kHz to 30 MHz, which makes 20 MHz squarely within this range. The A-band is used for various communications purposes, especially in long-distance radio transmission where shorter wavelengths are utilized.

To understand the context of the other bands briefly, the C-band usually operates from 4 to 8 GHz, and W-band typically refers to frequencies from approximately 75 to 110 GHz, while the U-band covers frequencies from around 300 MHz to 3 GHz. None of these ranges would include the 20 MHz frequency, thereby affirming that the A-band is indeed the appropriate classification for a signal at this frequency.