Dual-function radar and communications (DFRC) systems implement radar and communications on the same platform, which lead to substantial gains in performances as well as the system cost, weight, and power consumption. Recently, a spatial modulation based communication radar (SpaCoR) system, which has improved data rates and radar angular resolution compared with the techniques using fixed antenna allocation, was proposed to facilitate the co-existence of both functionalities on the same platform. In this paper, we implement a prototype with dedicated hardware and software components to verify the feasibility of SpaCoR. In addition to realizing SpaCoR, this prototype can be utilized to demonstrate a multitude of DFRC systems as it consists of multiple modules including baseband waveform generation, over-the-air signaling, frequency band waveform transmission, radar echo generation, radar echo reception, and communication signal reception. We evaluate SpaCoR using actual passband waveforms with over-the-air signaling. The results show that the communications subsystem of SpaCoR achieves improved bit error rate (BER) performance compared to the fixed allocation system when using the same data rate. For the radar subsystem, the experiments show that spatial agility of SpaCoR leads to improved angular resolution.