RECEIVER_PREAMPLIFIER

Published:2009/7/13 2:45:00 Author:May | From:SeekIC

This preamplifier lets you use a short antenna over the range from 100 kHz to well over 55 MHz, with excellent sensitivity, using a vertical 30-in piece of #12 wire or a few feet of wire laying on the floor. Transistor Q1 (NPN) is directly coupled to PNP transistor Q2. Feedback from the collector of Q2 to the emitter of Q1 is accomplished by resistors RF and RA. Because of the high open-loop gain of the amplifier, the gain of the amplifier is RF/RA, or 20 dB maximum. A 1-kΩ potentiometer changes the effective value of RA resulting in a minimum gain of near unity.



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