AFSK_SHIFTS_UP_TO_20_kHz

Published:2009/7/14 22:50:00 Author:Jessie | From:SeekIC

Wide-range generator can be tuned from 50 Hz to 20 kHz, for shifting between two frequencies as much as 20 kHz apart. UI is 555 timer connected as astable MVBR. When Q3 is biased off, charge/discharge currents for C1 flow chiefly through R1 and R2 to determine lower frequency of oscillation, When Q3 is on, R2 is effectively shorted and frequency is increased.Q1 acts as buffer and inverter so higher voltage at input gives higher tone. Keying occurs when input voltage exceeds 1 V with 5-V supply. If 10K supply resistor for al is reduced to 1000 ohms, keying voltage increases to 3V.-T. M. Whittaker, Wide-Range AFSK Generator, QST, May 1977, p 48.



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