Charles Stuart Ballantine (September 22, 1897 – May 7, 1944) was an American electronic engineer and inventor.
In 1920-1921 he undertook graduate studies in mathematical physics at Harvard University, then spent a year at the Radio Frequency Laboratories in Boonton, New Jersey, where he worked on radio receivers and made inventions for stabilization of radio-frequency amplifiers via a Wheatstone bridge, linear detection at high signal levels, and automatic volume control.
From 1924 to 1927 Ballantine carried out independent studies of radio propagation in White Haven, Pennsylvania, then was briefly research director at the Radio Frequency Laboratories, and in 1929 collaborated with F. M. Huntoon in studying the effects of high pressure on bacteria.
From 1929 to 1934 he was President of the Boonton Research Laboratories investigating errors in microphones due to diffraction and cavity resonance, and developing new devices including an electrostethoscope, automatic optical recorder for frequency-response measurements, and logarithmic voltmeter.
Ballantine held more than 30 patents, and was a Fellow of the American Physical Society, the Acoustical Society of America, and the Institute of Radio Engineers, as well as a member of the American Association for the Advancement of Science and the Franklin Institute.