Beat-Frequency Audio Generator

  
Ql is a fixed oscillator operating at 455 kHz. Ul is a mixer, with its own internal oscillator running at 45
Beat-Frequency Audio Generator - schematic

5 kHz. FIL1 and FIL2 are Murata CSB455E filters or equivalent. Dl is a varactor diode (an IN4002 used as a varactor works well here). R6 controls the bias on Dl. When R6 is varied, the oscillator frequency varies a few kHz. Audio beat note is taken, through RF filter L2 and CIO, from pin 5 of Ul.




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