Demonstration circuit DC2070A is optimized for evaluation of the LTC5577 high signal level active downconverting mixer. Its RF input port is matched to 50Ω from 1.3GHz to 4.3GHz with 12dB return loss, and the LO port is matched to 50Ω from 950MHz to 4.1GHz with 10dB return loss. The RF and LO inputs are easily matched for higher or lower frequencies with simple external matching, as low as 350MHz and 300MHz, respectively. The low capacitance differential IF output is usable up to 1.5GHz. The LTC5577 active mixer is optimized for RF downconverting applications that require high input signal handling capability and wide bandwidth.