Above 300 GHz, Schottky-based room-temperature heterodyne systems allow to detect THz radiation to the order of <;0.1 K of physical temperature variations in optical blackbodies with unequaled spectral resolution. In this paper we examine some of the parameters of these low-noise and high-resolution detection systems in order to enhance their future use in the generation/detection of free space THz-carrier modulated signals. We propose and demonstrate a novel way to generate QPSK modulated signals through the bias voltage of the last multiplier element of the emitter chain that yet could reach > mW of emitted power and a signal bandwidth of several tenth of gigahertz.