Doc Ewen: The Horn, HI, and Other Events in US Radio Astronomy

Slide 14: Detecting the Interstellar Hydrogen Line, 1951

Page 2 of Purcell's funding request letter, with itemized list including antenna ($150), APT-5 xmtr ($100), power supply ($75), mixer parts ($100), and waveguide ($75), for a grand total of $500. [Photo courtesy of Doc Ewen]
Slide 15