# AM radio at night **URL:** \ **Category:** Factual Questions\ **Created:** [November 12, 2006, 6:00pm UTC](https://boards.straightdope.com/t/am-radio-at-night/380124 "2006-11-12T18:00:18Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![caturday](https://avatars.discourse-cdn.com/v4/letter/c/a87d85/32.png) [@caturday](https://boards.straightdope.com/u/caturday)\ **Post date:** [November 12, 2006, 6:00pm UTC](https://boards.straightdope.com/t/am-radio-at-night/380124/1 "2006-11-12T18:00:18Z")
Why do AM radio stations have to turn down their power at night? The only answer I was able to find says there’s a change in the ionosphere. What is the change, the cause and the reason? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [November 12, 2006, 6:04pm UTC](https://boards.straightdope.com/t/am-radio-at-night/380124/2 "2006-11-12T18:04:56Z")
A [recent thread](http://boards.straightdope.com/sdmb/showthread.php?t=391660) on this subject. ---
**Author:** ![Jonathan\_Chance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jonathan_chance/32/701_2.png) [@Jonathan\_Chance](https://boards.straightdope.com/u/Jonathan_Chance)\ **Post date:** [November 12, 2006, 6:05pm UTC](https://boards.straightdope.com/t/am-radio-at-night/380124/3 "2006-11-12T18:05:18Z")
It’s been helluva long time since my broadcasting course but I seem to recall that the sun dampens the ability of AM signals to get through the atmosphere. So when the sun isn’t in the sky lower power will carry farther. ---
**Author:** ![Scruloose](https://avatars.discourse-cdn.com/v4/letter/s/e68b1a/32.png) [@Scruloose](https://boards.straightdope.com/u/Scruloose)\ **Post date:** [November 12, 2006, 6:13pm UTC](https://boards.straightdope.com/t/am-radio-at-night/380124/4 "2006-11-12T18:13:20Z")
It’s SOP for the radio biz. From their business plan: 1. Reduce power at night. 2. ? 3. Profit!