A sensing electrode consisting of electrically nonconductive underlay, made up of polymeric matter, with pH sensitive antimony layer deposited onto, which is connected by means of a secondary conductor with a measurement device in a place, which is out of reach of the system, of which pH is measured. The housing has a panel, which includes a plurality of first holes. Various support and storage modules or components are adapted to be contained within the interior of the cabinet, including stock rests for positioning in the bottom of the cabinet interior, as well as barrel rests and pistol supports that are secured to amounting member which may be adjustably positioned within the storage cabinet interior. The probe is used by placing a portion of the insulating material surrounding the probe conductor in contact with a circuit such as an RF microstrip carrying an RF signal to be monitored. A level of one or both of a mono component and a stereo component of an FM multiplex signal may be controlled based on the SNR.