Experimental evaluation of a high-temperature superconducting Josephson heterodyne mixer based on a resistive-SQUID configuration is reported. The device consists of two YBa 2Cu 3O 7-x step-edge Josephson junctions connected via a small resistor in an otherwise superconducting loop. It has been previously shown to generate a heterodyne oscillation, which is frequency-tunable by a control current through the resistor. Under certain conditions, this device can operate as a frequency-tunable heterodyne mixer (down-converter) in the presence of an RF signal. In this paper, we describe the operation of the autonomous Josephson mixerlocal oscillator device and present the experimental results on the mixer performances in terms of the junction currentvoltage characteristics, the frequency tunability, linearity, and dynamic range as well as their temperature dependence for signal frequencies from 1 to 5GHz.