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This paper presents a new concept in RF multiplexer design to integrate a single monopole-type antenna to a receiver with large, multiband tuning ranges. Traditional techniques to integrate a single antenna with such receivers are limited in their ability to handle simultaneous channels distributed over very large tuning ranges, which is important for frequency-agile cognitive radio, surveillance, and other applications requiring wideband or multiband monitoring. In our approach, the goal is first to achieve sensitivity which is nominally dominated by external (environmental) noise, and then secondly to improve bandwidth to the maximum possible consistent with this goal. A procedure is described for designing antenna-multiplexer-preamplifier assemblies using this philosophy. It is shown that the approach can significantly increase the usable bandwidth and number of bands that can be supported by a single, traditional antenna. A three channel (10-28 MHz, 32-50 MHz, and 54-80 MHz) multiplexer for a VHF monopole antenna was designed and performance was validated through field experiment.