New AM Antenna Protection Rules Cris Alexander, CPBE, AMD, DRB Crawford Broadcasting Company Aurora, Colorado

Introduction It has long been recognized that metallic structures near AM radiators have the potential to produce undesired effects on the radiation pattern FCC “Newcomer Policy” – a newcomer… is responsible, financially or otherwise, for taking steps necessary to eliminate objectionable interference to other stations.

Introduction There has always been ambiguity about what constitutes “objectionable interference.” The FCC has, in many cases, been reluctant to apply the newcomer policy to cases of reradiation.

Introduction Rules have long been in place in Part 22 (Public Mobile Service), Part 27 (Wireless) and Part 73 (Broadcast) requiring specific actions within a certain distance of an AM antenna. No rules existed for Part 90 (Private Land Mobile) or any other service. Those services could build near AM arrays without study or mitigation.

Coalition Starting in 2008, the AM Directional Antenna Performance Verification Coalition began working with the FCC to adopt new universal rules for AM antenna protection. These new rules were enacted in August of 2013 – still awaiting OMB approval. Contained in Part 1 (Practice and Procedure) – universal to all services.

Screening Distances Based on wavelength at AM frequency For non-directional (ND) stations, screening distance is one wavelength. For directional (DA) stations, screening distance is 10 wavelengths or 3 km, whichever is less. CDBS array center coordinates are to be used to calculate distances.

Screening Heights For ND stations, screening height is 60 electrical degrees. For DA stations, screening height is 36 electrical degrees. Building-mounted antenna supports must be considered only if the tower or antenna structure itself exceeds the applicable threshold height. –The building height is not considered.

Non-Directional Screening

Directional Screening

Building Screening

Significant Modification Criteria Altering the physical height by more than 5 electrical degrees. Any addition/replacement of antenna or transmission line on a detuned or base- insulated tower.

Modification Screening

Disturbance Criteria For ND stations, 2 dB. For DA stations, any radiation in excess of the AM station’s licensed standard pattern. Proponent must provide AM licensee 30 days written notice prior to construction or modification.

Moment Method Analysis Moment-method analysis is to be used to determine the potential effects of an antenna structure within the screening distance and in excess of the screening height. No model calibration is required. § modeling criteria must otherwise be used.

Field Measurements For conventionally-licensed AM stations, pre/post-construction monitor point measurements can be made instead of moment-method analysis. MP field strengths are not always a good indicator of the impact of a nearby potentially reradiating structure.

Outside the Screen Tower construction/modification that falls outside the screen criteria is presumed to have no impact on the AM antenna. When an AM station is impacted by such construction/modification outside the screen (or when the AM licensee believes his antenna will be impacted), a showing can be submitted using moment-method analysis or field measurements. Must be provided to the proponent if not yet constructed, and to the FCC within two years of completion of the structure.

Outside the Screen (cont’d) FCC can order detuning. Once notified, the applicant is held up from construction or application unless notification and corrective action are provided by the applicant.

Existing Reradiating Structures One-year window from effective date of rules to submit showing. Moment-method or field measurement analysis. FCC can order detuning if indicated.

A Moment-Method Analysis Example 3-tower 5 kW AM directional array on 1330 Part 90 tower located 320 meters away –Azimuth to tower: deg. True –Height of tower: 45.7 meters Step 1: Construct and run a control model of only the AM array Step 2: Add the other tower to the model and run