AM Antenna Protection Rules: Guidelines and Procedures

1. New AM AntennaProtection Rules Cris Alexander, CPBE, AMD, DRB Crawford Broadcasting Company Aurora, Colorado

2. Introduction • It has long been recognized that metallic structures near AM radiators have the potential to produce undesired effects on the radiation pattern • With the rollout and expansion of the cellular telephone network, the FCC instituted rules to protect AM antennas from such effects

3. 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.

4. 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 • Contained in Part 1 (Practice and Procedure) – universal to all services

5. 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.

6. 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.

7. 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.

8. 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.

9. 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. • §73.151 modeling criteria must otherwise be used.

10. 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.

11. 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.

12. 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.

13. 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

14. A Moment-MethodAnalysis Example • 3-tower 5 kW AM directional array on 1330 • Part 90 tower located 320 meters away • Azimuth to tower: 298.61 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