Digital signal detection by a glow discharge detector

A glow discharge detector (GDD) is a plasma neon bulb originally designed for lighting. However, it was demonstrated that it can be used for the detection of electromagnetic radiation in a wide range of frequencies up to millimeter and submillimeter waves. It is shown here that the device can be used not only as a detector but also as a heterodyning mixer. Experimental measurements confirm an analytical derivation, demonstrating that quadrature modulated signals can be downconverted to an intermediate frequency (IF) without distortions, even if the amplitude and phase are modulated simultaneously, as in quadrature amplitude modulation (QAM) waveforms. Digital QAM waves at the microwave frequencies were directly illuminated onto the GDD and mixed with radiation produced by a local oscillator. The resulted GDD current was analyzed to verify that the product maintains its QAM constellation also at the IF. The GDD detects both the magnitude as well as the phase in a manner that allows the complete demodulation of the digital data using several modulation methods. The experimental setup, as well as the results, is presented. It is concluded that the GDD can be employed also as a direct mixer in a digital receiver chain. The notation 'GDM' is proposed for it which stands for 'glow discharge mixer.'