{
  "id": "emitters:fm-broadcast-tower",
  "collection": "emitters",
  "slug": "fm-broadcast-tower",
  "name": "FM / TV broadcast transmitter",
  "summary": "Broadcast sites radiate tens to hundreds of kilowatts ERP — thousands of times a cell sector — but from tall masts in the 30–300 MHz band where the FCC's public limit is at its most restrictive.",
  "status": "verified",
  "lastVerified": "2026-08-12",
  "data": {
    "aliases": [
      "radio mast",
      "broadcast antenna",
      "TV transmitter"
    ],
    "category": "radiofrequency",
    "environment": [
      "outdoor"
    ],
    "bands": [
      {
        "label": "FM broadcast (88–108 MHz)",
        "minHz": 88000000,
        "maxHz": 108000000
      },
      {
        "label": "VHF/UHF television",
        "minHz": 174000000,
        "maxHz": 700000000
      }
    ],
    "transmitPower": {
      "quantity": "power",
      "unit": "W EIRP",
      "value": 100000,
      "basis": "regulatory",
      "note": "100 kW ERP is a mid-size FM allocation; licensed powers range from a few hundred watts to over 1 MW ERP for some TV facilities.",
      "sourceIds": [
        "fcc-oet65"
      ]
    },
    "dutyCycle": "Continuous, constant-envelope transmission — unlike cellular, there is no traffic-dependent variation.",
    "distanceProfile": [
      {
        "meters": 100,
        "value": {
          "quantity": "power-density",
          "unit": "µW/m²",
          "value": 796000,
          "basis": "computed",
          "method": "S = EIRP / (4πd²) with EIRP = 100000 W, d = 100 m",
          "note": "Main-beam free-space value; broadcast antennas concentrate energy toward the horizon, not the tower base.",
          "sourceIds": [
            "fcc-oet65"
          ]
        }
      },
      {
        "meters": 500,
        "value": {
          "quantity": "power-density",
          "unit": "µW/m²",
          "value": 31800,
          "basis": "computed",
          "method": "S = EIRP / (4πd²) with EIRP = 100000 W, d = 500 m",
          "note": "Main-beam free-space value.",
          "sourceIds": [
            "fcc-oet65"
          ]
        }
      },
      {
        "meters": 2000,
        "value": {
          "quantity": "power-density",
          "unit": "µW/m²",
          "value": 1990,
          "basis": "computed",
          "method": "S = EIRP / (4πd²) with EIRP = 100000 W, d = 2000 m",
          "note": "Main-beam free-space value.",
          "sourceIds": [
            "fcc-oet65"
          ]
        }
      }
    ],
    "mitigations": [
      {
        "action": "Check the FCC ASR and licence records for ERP, height and antenna pattern before estimating exposure.",
        "effect": "Broadcast exposure is dominated by height and pattern, which vary enormously between sites.",
        "sourceIds": [
          "fcc-asr"
        ]
      },
      {
        "action": "Measure with a meter that covers 88–700 MHz; many consumer RF meters start at 200 MHz or higher and will read near zero next to an FM mast.",
        "effect": "Prevents a false negative caused by the meter's lower frequency limit."
      }
    ],
    "measureWith": [
      "broadband-rf-meter",
      "spectrum-analyser"
    ],
    "related": [
      "limits:fcc-mpe-public-30-300"
    ]
  },
  "sources": [
    {
      "id": "fcc-oet65",
      "title": "OET Bulletin 65: Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields",
      "publisher": "Federal Communications Commission, Office of Engineering and Technology",
      "url": "https://www.fcc.gov/general/oet-bulletins-line",
      "year": 1997,
      "kind": "government",
      "retrieved": "2026-08-12"
    },
    {
      "id": "fcc-asr",
      "title": "Antenna Structure Registration (ASR) public access database downloads",
      "publisher": "Federal Communications Commission",
      "url": "https://www.fcc.gov/wireless/data/public-access-files-database-downloads",
      "kind": "government",
      "retrieved": "2026-08-12"
    },
    {
      "id": "fcc-1310",
      "title": "47 CFR § 1.1310 — Radiofrequency radiation exposure limits",
      "publisher": "U.S. Government Publishing Office (eCFR)",
      "url": "https://www.ecfr.gov/current/title-47/section-1.1310",
      "kind": "regulation",
      "retrieved": "2026-08-12"
    }
  ],
  "links": {
    "self": "https://emfbase.com/api/emitters/fm-broadcast-tower",
    "html": "https://emfbase.com/emitters/fm-broadcast-tower",
    "markdown": "https://emfbase.com/emitters/fm-broadcast-tower.md",
    "collection": "https://emfbase.com/api/emitters"
  }
}