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

Slide 19: Detecting the Interstellar Hydrogen Line, 1951

The mixer. The mixer design was taken from the Rad Lab book on Mixers by Bob Pound [Microwave Mixers, by Robert V. Pound. MIT Radiation Laboratory Series 16, published by McGraw-Hill, 1948]. The mixer shown in the book operates at S-Band, hence, the scale factor was approximately 2 X. Bob was very helpful on this matter, as well as on many others. He is the type of fellow you like to have around when you’re building a hydrogen line receiver. On a visit to the Bell Telephone Research Lab at Homdel, NJ, suggested by Purcell, Harold Friis gave me (in his words) "two of the best 1N21 crystals ever tested". They were measurably better than any in the batch I had scrounged from my friends on Vassar St. at MIT. One was in the receiver on the night of March 25, 1951. [Diagram courtesy of Doc Ewen]
Slide 20