Radio 101: Why AM stations reduce power at night

Why can’t I hear my Relevant Radio® station at nighttime? It’s a question we hear often from listeners who don’t receive as clear a signal after sunset as they do during the day. But what most listeners don’t know is that this is a result of physics and the law.

The Federal Communications Commission (FCC) oversees broadcasting and radio, TV, satellite, and cable communications in the United States. They implement and enforce laws and regulations that networks and stations must follow in order to continue broadcasting in the US.

One of those FCC regulations pertains to nighttime broadcasting. According to the FCC website:

“Most AM radio stations are required by the FCC’s rules to reduce their power or cease operating at night in order to avoid interference to other AM stations.  FCC rules governing the daytime and nighttime operation of AM radio stations are a consequence of the laws of physics.  Because of the way in which the relatively long wavelengths of AM radio signals interact with the ionized layers of the ionosphere miles above the earth’s surface, the propagation of AM radio waves changes drastically from daytime to nighttime.  This change in AM radio propagation occurs at sunset due to radical shifts in the ionospheric layers, which persist throughout the night.”

Basically, because of the way radio waves travel at night, many Relevant Radio AM stations are require to reduce power when the sun sets in order to avoid massive interference with other stations.

The good news is that Daylight Savings Time is on the horizon—March 8 this year—meaning we’ll be gaining an extra hour of daylight. As summer approaches, the days also lengthen, giving you more time with your local Relevant Radio station at full power.

If the reduced power at nighttime affects your listening, try tuning in via these other means:

  • Live streaming online at
  • Listen live on the free Relevant Radio app
  • Stream on a smart speaker, like an Amazon Echo or Google Home
  • Podcasts of any shows you missed

Now you can amaze your friends with your new knowledge! Isn’t radio broadcasting a fascinating thing?

Lindsey is a wife, mother, and contributing author at Relevant Radio. She holds a degree in Journalism and Advertising from the University of Wisconsin-Milwaukee. Lindsey enjoys writing, baking, and liturgical living with her young family.