432_MHz_LOW_NOISE_PREAMP

Published:2009/7/15 23:04:00 Author:Jessie | From:SeekIC

Uses Fairchild FMT4575 transistor having 1.25-dB noise figure, equaling performance of best paramps at 432 MHz. Input matching circuit is low-loss low-Q L matching section L1-CR1. Value of blocking capacitor C1 is not critical, but should be low-loss high-Q type, Hot-carrier diode CR1 in matching section adds about 0.75 pF to circuit, and serves also as low-loss limiter that protects transistor from excessive RF. Zener-diode biasing permits direct grounding of emitter, is insensitive to transistor current gain, provides some DC protection to transistor, and requires no adjustments.-J. H. Reisert, Jr., Ultra Low-Noise UHF Preamplifier, Ham Radio, March 1975, p 8-19.



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