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 ID: 163341
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New AM AntennaProtection Rules
Cris Alexander, CPBE, AMD, DRBCrawford Broadcasting CompanyAurora, ColoradoSlide2
IntroductionIt 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 effectsSlide3
IntroductionRules 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.Slide4
CoalitionStarting 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 2013Contained in Part 1 (Practice and Procedure) – universal to all servicesSlide5
Screening Distances
Based on wavelength at AM frequencyFor 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.Slide6
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.Slide7
Significant Modification Criteria
Altering the physical height by more than 5 electrical degreesAny addition/replacement of antenna or transmission line on a detuned or base-insulated tower.Slide8
Disturbance Criteria
For ND stations, 2 dBFor 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.Slide9
Moment Method AnalysisMoment-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.Slide10
Field MeasurementsFor 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.Slide11
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.Slide12
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.Slide13
Existing Reradiating Structures
One-year window from effective date of rules to submit showingMoment-method or field measurement analysisFCC can order detuning if indicatedSlide14
A Moment-MethodAnalysis Example
3-tower 5 kW AM directional array on 1330 Part 90 tower located 320 meters awayAzimuth to tower: 298.61 deg. TrueHeight of tower: 45.7 metersStep 1: Construct and run a control model of only the AM array
Step 2: Add the other tower to the model and runSlide15Slide16Slide17Slide18Slide19Slide20Slide21