I was wondering how many watts an AM radio station outputs, and if I can calculate the watts on a tuned antenna by this equation:


Where Win = the watts input for the antenna, Wout = the watts output for the radio station, r = distance from the transmitter, and Y = how much rf the antenna gets from that square metre (I'm expecting Y to be like 0.1% or something because it's a pretty small antenna).

  • \$\begingroup\$ Which radio station? Some are hundreds of kW. \$\endgroup\$
    – user16324
    Jan 23, 2021 at 12:59

1 Answer 1


There is no simple answer. Working from ((old)) memory, transmitter output power ranges from 5 kW to over 50 kW. Then the antenna has a shaped radiation pattern (after all, why waste power radiating upward?); it is not a simple point source radiator that so many formulae are based on. Then you get into multi-antenna phased arrays for serious directionality.

Most radio stations have a website and a Wikipedia page. Between the two you should be able to find out the basics for stations near you: transmitter power and ERP - effective radiated power.

  • \$\begingroup\$ Going from lyrics to popular songs about the border radio days, I think 50kW is about right for the top end. Although I did find one reference to a 150kW station. en.wikipedia.org/wiki/XEPRS-AM \$\endgroup\$
    – user57037
    Jan 23, 2021 at 4:39
  • \$\begingroup\$ The FCC has a query page for AM stations: fcc.gov/media/radio/am-query \$\endgroup\$ Jan 23, 2021 at 5:45
  • \$\begingroup\$ Transmitter output powers start much lower than 5 kW, with many 1 kW stations and a handful even lower. If the 5th column starts with ND, it's nondirectional, so you can model it as a quarter-wave monopole. If it's DA, a directional antenna, you have more work, and if you want to dig even deeper you can find out ground conductivities too. \$\endgroup\$ Jan 23, 2021 at 5:50
  • \$\begingroup\$ @MarkLeavitt The border radio stations are not under the purview of the FCC. \$\endgroup\$
    – user57037
    Jan 23, 2021 at 7:28

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