How can high sensitivities be achieved across a large spectral range? With high-resolution gigahertz and terahertz spectroscopy, for instance. This technology from the University of Cologne achieves these sensitivities with high-frequency signals from an arbitrary function generator (shown here as a DAC), two mixers and local oscillators, a demodulator, and a fast analog-to-digital converter (ADC). They are connected as the figure shows. A local oscillator and the DAC, assisted by the mixer, generate an analog polychromatic excitation signal, which is coupled into the sensing device or measuring path where the sample molecules to be analyzed are located. After the RF signal has run through the measuring path once, a second mixer and a second local oscillator are used to mix it so that the two mixed sidebands lie one above the other and are offset as two frequency combs. Sample signal and reference signal are brought to cancellation for empty sample cells so that a signal arises only when the sample is present, greatly increasing the measurement method’s sensitivity.