Today, equipment is available from several AM antenna system manufacturers which will provide the ability to co-locate communications transmission systems on both single antenna and multiple tower AM antenna systems. Companies have equipment which once installed, insures that the wireless antenna and coaxial cable installations have virtually no effect on the host AM tower(s), and the AM signal has no effect on the wireless antenna. Moreover, additional antennas and transmission lines can be added to the tower in the future without re-engineering the AM isolation. This means the owner can lease additional space to other wireless carriers, limited only by the tower structural capability.
On non-directional towers, an advanced folded unipole isolation system is typically used. This results in direct grounding of the AM tower. Wireless antennas and transmission lines are mounted and bonded directly onto the structure. The folded unipole uses a unique wire cage impedance transformer. In one implementation, lower portions of the cage are heavily insulated and spaced away from the tower to allow ready operational access to the wireless antenna system by tower climbers, even while “hot.” Such folded unipole tower collocation systems benefit the AM station with improved efficiency, “air sound”, and lightning protection, thus enhancing the tower collocation experience for the station. Conversion to an advanced folded unipole type tower collocation system may entail replacing the station’s ATU (antenna tuning unit) and some “on tower” construction.
Directional stations use multiple towers to form an FCC licensed radiation pattern crucial to protecting other stations from interference. This licensed pattern may not be disrupted by tower collocation. The cost-effective approach to this end is to employ specially designed isolation systems between the base station equipment and the AM tower.