High dynamic range receiver front end mixer requiring low local

Abstract

An improved circuit utilized in an RF tuner or receiver for selecting and nverting an RF signal to an intermediate frequency with reduced injection power requirements.The circuit is utilized in the 'front end' of a radio frequency receiver or tuning section, the purpose being to convert the received RF signal to an intermediate frequency. The improved circuit comprises and includes a diode sampling bridge coupled to an RF signal receiving source, such as an antenna, a local oscillator coupled across the bridge providing pulses for actuating and turning on particular diodes of the bridge for a relatively short length of time. The bridge output is coupled to a selecting transistor, which may include a crystal filter coupled to the emitter of the transistor. The pulsing signal across the diode bridge is relatively short in comparison with the received RF signal. When the diode sampling bridge is conducting, the RF signal is mixed and passed to the selecting transistor base. The selecting transistor, with its emitter coupled to the crystal filter, amplifies only a signal of a desired frequency. The short pulse actuation in the front end for mixing requires less injection power, allowing the circuit to be adapted for use with battery powered equipment.