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Duplex Transverter for 900, 800, 700 and 450MHz bands. CPE and Base

This is a general purpose design though the first application was to use a 2MHz bandwidth Cable Modem (DOCSIS) on FDD 874MHz and 919MHz.

Architecture

Full duplex using a duplex filter on the aerial connecting to RF LNA and RF PA. The Modem connects via a typical cable broadband Diplexer. A single chip dual PLL/Synth controls the up converter and downconverter VCOs that drive the doubly balanced diode ring mixers. A PIC micro sets the PLL/Synth dividers and prescalers.

An onboard superhet / FSK receiver measures a beacon carrier and thus the CPU can select high or low gain for the receiver converter.