Iridium External Magnet Mount Antenna. The M1621HCT-EXT is a high performance Iridium certified antenna designed for the Iridium network, built on proprietary Maxtena HeliCore® technology. This technology provides exceptional pattern control, polarization purity and high efficiency in a very compact form factor. The M1621HCT-EXT is an external magnet mount antenna, featuring a 1,500 mm LRM100 coaxial cable with integrated connector. The very small size and light weight make this helical Iridium antenna unique in the market and perfect for various commercial and industrial applications. This antenna is the ideal solution for the most extreme and demanding applications where reliable satellite reception and high accuracy are required. It can be used to boost the performance of the Iridium handsets among other uses.