New AM Antenna Protection Rules
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Transcript of New AM Antenna Protection Rules
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New AM AntennaProtection Rules
Cris Alexander, CPBE, AMD, DRBCrawford Broadcasting Company
Aurora, Colorado
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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.
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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.
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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.
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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.
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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.
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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.
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Non-Directional Screening
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Directional Screening
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Building Screening
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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.
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Modification Screening
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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.
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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.
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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.
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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.
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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.
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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.
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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
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