ULTRASONIC_cw_TRANSCEIVER

Published:2009/6/24 21:33:00 Author:Jessie | From:SeekIC

With the telegraph key at S2 up (open), the 567 PLL's input at pin 3 is coupled to the output of Q3. Transistors Q3 and Q4 are operat-ing in a high-gain, two-stage audio-amplifier circuit. The piezo speaker is coupled to the in-put of the amplifier though a 0.1-μF capacitor and a 680-Ω isolation resistor.In the receive mode, the piezo speaker oper-ates as a sensitive microphone. Ultrasonic signals travel from the microphone through the two-stage amplifier to the input of the 567, and, if the signal's frequency is within the IC's bandwidth, the LED will light and piezo-sounder BZ1 will sing out foreach dit and dah received. The receiver can be tuned to the incoming ultrasonic signal by adjust-ing R17. Of course, adjusting that potentiometer also changes the transmitter's frequency.The transmitter operates each time the S2 is closed. When the key is closed, diode D3 supplies a path to ground for BZ1, causing that sounder to produce an audible signal for each dit and dah transmitted. Also, Q2's bias is taken to ground through D2, allowing Q1 to pass the 567's square-wave signal on to the input of the power amplifier and out through the speaker.



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