This paper presents the implementation of a high-efficiency radiofrequency (RF) harvester, which consists of a rectenna and a maximum power point tracker (MPPT). The rectenna was characterized from -30 dBm to -10 dBm at 808 MHz, achieving an efficiency higher than 60% at -10 dBm. Experimental results also show that the rectenna can be well modelled as a Thévenin equivalent circuit, which allows the use of a simple ensuing MPPT. The complete RF harvester was tested, achieving an overall efficiency near 50% at -10 dBm. Further tests were performed powering a sensor node from a nearby antenna.