118:. A station whose maximum coverage would otherwise be available at 4500 watts (given a specific directional pattern and antenna system efficiency) had a choice of either living with 2500 watts, or reducing the antenna efficiency to a level which would allow for 5 kW. Newly constructed stations could fairly easily design an antenna system to meet the requirements, but stations on or moving to a shared tower with higher efficiency had a problem. The resistor network exception was created to allow stations to reduce their antenna efficiency without having to modify the existing tower.
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Rule changes in the 1980s did away with the fixed set of power choices, allowing stations to choose an appropriate power level for their antenna system ("dial-a-power"), so there should no longer be any need for the concept of nominal power. However, stations still take advantage of the resistor
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Nominal power is ultimately a historical artifact of the regulatory regime employed by the FCC prior to the 1980s. In the old system, rather than allowing licensees to choose any power level which would meet the efficiency and
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exception in some cases, simply because they perceive the marketing advantage of higher power (or at least "round" power) to be worth the cost of the wasted energy.
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standards for their class, stations were restricted to a small set of power levels: 50, 100, 250, 500, 1000, 2500, 5000, 10000, 25000, and 50000
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In both cases, nominal power excludes losses in transmission lines between the tower or
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185:"All-Digital AM Broadcasting, Revitalization of the AM Radio Service"
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stations, nominal power is normally equal to the RF power at the
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power presented to the antenna, as determined from the base
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used to decrease the efficiency of the antenna system.
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36:. AM broadcasters are licensed by the
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161:"RADIO BROADCAST SERVICES"
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132:Effective radiated power
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191:. 30 December 2020
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