The paper deals with the design of a test link for the characterization of a hybrid Free Space Optical/Radio-Frequency (FSO/RF) atmospheric channel. The ever-increasing demand on broadband connectivity, specifically in the Last-Mile networks, leads to the use of Free-Space optical systems in combination with RF systems above 100 GHz, which are able to reach data rates in the order of 10 Gb/s. However, both systems are strongly influenced by weather conditions. A significant increase in the link availability can be achieved by combining both technologies. An optimum design of such systems requires reliable models of atmospheric channels. The test link presented in this paper is intended for long-term monitoring of atmospheric attenuation and turbulence in the optical band at 850 nm and 1550 nm, and in the millimeter band at 122 GHz. The bandwidth of both measuring systems has been chosen narrow but sufficient for capturing all important phenomena. This results in the dynamical range of nearly 50 dB, which is not available from the RSSI signal of commercial broadband systems.