NMO mounts are a specialized hardware solution for securely attaching antennas to vehicle roofs or control boxes. These mounts are characterized by their ability to create a weatherproof seal and accommodate coaxial cable connections. Several styles of NMO mounts exist, differing primarily in how the connector is terminated and the size of the mounting hole required. The mounts utilize a rubber O-ring to ensure a watertight connection where the mount penetrates a metal surface, and a further seal is created when the antenna is screwed onto the mount. Installation techniques vary depending on the mount type, with considerations for cable routing and preventing damage to vehicle interiors.
NMO Mount Types and Hole Sizes
NMO mounts are available in different configurations to suit various applications. One common type is designed for use with a ¾ inch diameter hole, typically used for mounting antennas on vehicle roofs. Another version is designed for mounting in 3/8 inch diameter holes in panels up to ½ inch thick. The documentation details connector part numbers including 931-1303-ND, 931-1343-ND, 931-1302-ND, 931-1309-ND, 931-1305-ND, 931-1342-ND, 931-1306-ND, 931-1307-ND, 931-1304-ND, 931-1308-ND, 931-1311-ND, 931-1312-ND, 931-1310-ND, and 931-1313-ND, alongside corresponding cable designations CAB.V09, CAB.W05, CAB.V08, CAB.W09, CAB.V11, CAB.V05, CAB.V12, CAB.V13, CAB.V10, CAB.W08, CAB.W11, CAB.W12, CAB.W10, and CAB.W13.
Installation Procedure for ¾ Inch NMO Mounts
The installation of a ¾ inch NMO mount typically involves drilling a ¾ inch hole in the mounting surface. The process is designed to allow for “fishing” the coaxial cable through the vehicle without requiring removal of the interior headliner. The cable is fed through the hole before the mount is inserted. A key feature of this mount is that the outer threaded area is slightly larger than ¾ inch in diameter, preventing the mount from falling through the hole even before the securing nut is applied. The mount is held at a slight angle during insertion to facilitate maneuvering it into the hole.
Weatherproofing and Sealing
Maintaining a weatherproof seal is critical for NMO mount installations. The design incorporates two sealing mechanisms: a rubber O-ring located on the underside of the brass nut, and a seal created when the antenna is screwed onto the NMO mount. However, user reports suggest that additional sealing measures may be considered. Some users recommend using black RTV sealant in conjunction with the provided rubber gasket to enhance the weather resistance of the installation. The documentation confirms that when installed correctly, the NMO mount provides a waterproof connection suitable for outdoor exposure.
Considerations for Radio Proximity
When installing multiple NMO mounts, particularly on a vehicle roof, proximity to other electronic equipment should be considered. A user inquiry specifically addressed the potential for interference between an NMO mount installation and a Motorola MCS2000 VHF radio operating at 100 Watts, alongside a Whelen Mini Edge light bar. The documentation does not provide specific guidance on safe separation distances between NMO mounts and other devices.
Cable Installation and Termination
Proper cable installation is essential for achieving a weather-tight seal. The coaxial cable is threaded through the mounting hole before the NMO mount is secured. The documentation emphasizes that correct installation ensures a weather-tight seal from the NMO mount on the exterior to the cable termination on the interior of the metal panel. The NMO mount system is considered a reliable solution for outdoor applications, offering years of operation when installed correctly.
Conclusion
NMO mounts provide a robust and weatherproof solution for antenna installation in outdoor environments, such as vehicle roofs and control boxes. Proper installation, including careful attention to hole size, cable routing, and sealing, is crucial for ensuring long-term reliability and performance. While the documentation details the inherent sealing mechanisms of the mount, user experience suggests that supplemental sealing with products like black RTV may be considered. Consideration should also be given to the proximity of other electronic equipment during installation to mitigate potential interference.