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D 1944 Rohde und Schwarz STT4032 Front Large.jpg - Hihiman
Goldschmidt tone wheel.jpg - Thomas H. White
Beat frequency oscillator board.jpg - 32RB17
Beat-frequency audio oscillator, General Radio, Cambridge MA, c. 1935 - Putnam Gallery - Harvard University - DSC08088.jpg - Daderot
Beat frequency oscillator "STI 4032" from German company Rohde und Schwarz (1944).jpg - Pittigrilli
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