How Much AM Power is Too Much?
As power on a tower goes up, potential carrier collocation issues increase. The feasibility of tower collocation is a matter of budget and operational convenience for both the AM and carrier. The choice of carrier isolation technology is an important factor in the analysis. In a directional array, the important factor is the power in the tower under consideration, not the licensed power. A thorough engineering investigation is necessary in all but the lowest power situations. Successful collocates can be done on 10,000 watt towers, but usually “lower is better”!
AM Directional Compatibility
Collocation on one or more towers of a directional array is often quite practical. In fact, in terms of maintenance flexibility, such installations can offer advantages over nondirectional tower collocations. A good directional array collocation requires a balance between carrier operational logistics and AM technical factors.
The number one factor in tower selection from a carrier perspective is convenience for fast and safe maintenance and/or system modifications. This suggests the choice of a tower that is inactive in one mode (preferably daytime) and that uses low power. At the same time, that tower should be low impedance and stable for minimum perturbation of array operation. Part of the equation is accessibility for roads and underground utilities without unreasonable disruption of AM transmission line and ground system elements.
For the protection of both the AM and the carrier, it is very important that coordination of RF grounding, equipment placement, interim operation and RF safety plans be accomplished and memorialized before construction begins.
Construction will inevitably result in some AM array disruption, and plans should be in place for appropriate FAA notices, FCC STA’s, power reduction, pattern changes, or other actions to facilitate the construction phase. Of course, associated costs should be factored into the lease agreement.