# Radio echo? **URL:** \ **Category:** Factual Questions\ **Created:** [May 11, 2007, 10:58pm UTC](https://boards.straightdope.com/t/radio-echo/403771 "2007-05-11T22:58:34Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![WF\_Tomba](https://avatars.discourse-cdn.com/v4/letter/w/d9b06d/32.png) [@WF\_Tomba](https://boards.straightdope.com/u/WF_Tomba)\ **Post date:** [May 11, 2007, 10:58pm UTC](https://boards.straightdope.com/t/radio-echo/403771/1 "2007-05-11T22:58:34Z")
I was driving in Iowa today, listening to 90.9 KUNI (Iowa Public Radio). For some reason the reception was bad–there was interference from other stations. But one of the main things that kept breaking in on the signal was a repeat of the KUNI signal itself, delayed by about 5-10 seconds. It was very surreal, especially since I was also hearing snippets of a religious radio station talking about God. What would cause this kind of “echo” effect? Edited to add: I forgot to say that this is the second time I have experienced this radio effect. Both times I was in the Midwest. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [May 11, 2007, 11:26pm UTC](https://boards.straightdope.com/t/radio-echo/403771/2 "2007-05-11T23:26:08Z")
Since EM waves would travel 930,000 miles and back in 10 seconds, I doubt that what you’re hearing is a true echo. You might be picking up a [Radio repeater station](http://en.wikipedia.org/wiki/Radio_repeater) that’s gotten out of synch. ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [April 28, 2010, 12:11am UTC](https://boards.straightdope.com/t/radio-echo/403771/3 "2010-04-28T00:11:10Z")
As I understand it, an omni-directional antenna sends the signal out in all directions more like a donut than a sphere. As such, couldn’t one sector of this donut arrive directly at the receiving antenna while another sector is taking a longer route by bouncing off some surface? Wouldn’t this create an echo? Is this possible? Of course, this begs me to ask why doesn’t this happen all the time? Are there filters in the radio that wipe out a similar signal slightly out of phase? (I am assuming the echoed signal would be out of phase.) ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [April 28, 2010, 12:12am UTC](https://boards.straightdope.com/t/radio-echo/403771/4 "2010-04-28T00:12:50Z")
Uh, my apologies to the mods. I am sorry for renewing an old post. I accidentally saw the wrong date not realizing this post is older than I realized. This was unintentional. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [April 28, 2010, 1:03am UTC](https://boards.straightdope.com/t/radio-echo/403771/5 "2010-04-28T01:03:04Z")
Still, the question about echos happening all the time is an interesting one. They do, but they do so on a shorter time scale than you picture. Remember “ghosting” on broadcast televisions, where a second faint image appears to one side of the main one? That second image is the echo. There are ways of dealing with it. Nowadays I don’t think there is much that is made difficult on this account, except that GPS signals are made less precise for things like surveying. GPS antennas are designed to ignore signals bouncing up from the ground, but it’s harder to handle big metal structures nearby. ---
**Author:** ![Kyrie\_Eleison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kyrie_eleison/32/7682_2.png) [@Kyrie\_Eleison](https://boards.straightdope.com/u/Kyrie_Eleison)\ **Post date:** [April 28, 2010, 1:58am UTC](https://boards.straightdope.com/t/radio-echo/403771/6 "2010-04-28T01:58:49Z")
> [@Napier](#): > > Nowadays I don’t think there is much that is made difficult on this account, except that GPS signals are made less precise for things like surveying. Beg to differ, for some definitions of “much.” Multipath propagation is still a problem for the transmission of digital television in some areas. I’m looking at you, WYDC, Elmira, NY. ---
**Author:** ![Pitter\_Patter](https://avatars.discourse-cdn.com/v4/letter/p/90db22/32.png) [@Pitter\_Patter](https://boards.straightdope.com/u/Pitter_Patter)\ **Post date:** [April 28, 2010, 2:09am UTC](https://boards.straightdope.com/t/radio-echo/403771/7 "2010-04-28T02:09:29Z")
I’m thinking maybe the OP was hearing another distant station via E skip which happened to be running the same program but it had been started slightly later than the local station. I hear 3 NPR stations here and often the programs are out of synch. Could also be due to differing audio processing chains. ---
**Author:** ![Lust4Life](https://avatars.discourse-cdn.com/v4/letter/l/ecc23a/32.png) [@Lust4Life](https://boards.straightdope.com/u/Lust4Life)\ **Post date:** [April 28, 2010, 12:02pm UTC](https://boards.straightdope.com/t/radio-echo/403771/8 "2010-04-28T12:02:43Z")
> [@Squink](#): > > Since EM waves would travel 930,000 miles and back in 10 seconds, I doubt that what you’re hearing is a true echo. You might be picking up a [Radio repeater station](http://en.wikipedia.org/wiki/Radio_repeater) that’s gotten out of synch. As an ex radio operator, this was first thought.