LOG_LIMITER

Published:2009/7/13 5:00:00 Author:May | From:SeekIC

Installed between microphone and AF input connector of transmitter to increase averdge level of human voice and corresponding SSB transmitter output signal.Preamp U1 increases audio input level to over-come loss of following high-pass filter. Lowpass filter after logamp U2 eliminates all energy above about 2950 Hz. Last opamp U3 sets out.put level of processor for driving station transmitter properly. Overall amount of amplitude limiting is determined by setting of preamp gain control R4. Higffipass filter eliminates 60-Hz hum developed in audio system or in accessory equipment and reduces harmonic distortion generated by deeply pitched voice or by hum picked up from tape recorder or phone patch.Gain of opamp is determined by CR1-CR2, which give logarithmic response to audio input amplitude. Adjust R2, R17, and R19 for minimum distortion while applying 1-kHz sine wave to input.-R. Myers, A Quasi-Logarithmic Ana-Log Amplitude Limiter with Frequency-Domain Processing, QST, Aug. 1974, p 22-25 and 40.



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