# Strange Radio Reception **URL:** \ **Category:** Factual Questions\ **Created:** [September 6, 2002, 3:05pm UTC](https://boards.straightdope.com/t/strange-radio-reception/127292 "2002-09-06T15:05:37Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Thinks2Much](https://avatars.discourse-cdn.com/v4/letter/t/73ab20/32.png) [@Thinks2Much](https://boards.straightdope.com/u/Thinks2Much)\ **Post date:** [September 6, 2002, 3:05pm UTC](https://boards.straightdope.com/t/strange-radio-reception/127292/1 "2002-09-06T15:05:37Z")
I live in the Chicago suburbs. Every once in a while, particularly yesterday, my FM radio reception is really strange. I can’t get any local stations clearly, but I can get places like Davenport Iowa, Dearborn Michigan, or less impressive, Madison Wisconsin, clear as a bell instead. Anyone know why? I haven’t seen any correlation with the weather. I know there was a day in August that did the same when it was 98 and humid. Yesterday was 80 and dry. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [September 6, 2002, 4:04pm UTC](https://boards.straightdope.com/t/strange-radio-reception/127292/2 "2002-09-06T16:04:51Z")
Wierdness in the Heaviside layer: > [@](#): > > In 1902 the American electrical engineer Arthur Edwin Kennelly and the British physicist and electrician Oliver Heaviside, independently and almost simultaneously, announced the probable existence of a layer of ionized gas high in the atmosphere that affects the propagation of radio waves. This layer, formerly called the Heaviside or Kennelly-Heaviside layer, is one of several layers in the ionosphere. Although the ionosphere is transparent to the shortest radio wavelengths, it bends or reflects the longer waves. Because of this reflection, radio waves can be propagated far beyond the horizon. Propagation of radio waves in the ionosphere is strongly affected by time of day, season, and sunspot activity. Slight variations in the nature and altitude of the ionosphere, which can occur rapidly, can affect the quality of long-distance reception. The ionosphere is also responsible for skip, the reception at a considerable distance of a signal that cannot be received at a closer point. This phenomenon occurs when the ground ray has been absorbed by the intervening ground and the ionospherically propagated ray is not reflected at an angle sufficiently steep to be received at short distances from the antenna. [http://www.qsl.net/nc4ar/radio.htm](http://www.qsl.net/nc4ar/radio.htm) ---
**Author:** ![Thinks2Much](https://avatars.discourse-cdn.com/v4/letter/t/73ab20/32.png) [@Thinks2Much](https://boards.straightdope.com/u/Thinks2Much)\ **Post date:** [September 6, 2002, 5:01pm UTC](https://boards.straightdope.com/t/strange-radio-reception/127292/3 "2002-09-06T17:01:04Z")
Cool. Thanks for the info. 🙂 ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [September 6, 2002, 5:17pm UTC](https://boards.straightdope.com/t/strange-radio-reception/127292/4 "2002-09-06T17:17:33Z")
Still, I didn’t think FM radio could travel that (as suggested in the OP) but only AM radio could. I know I got a Boise, Idaho, AM radio station in Phoenix, Arizona, one night. However, I don’t think I’ve ever gotten an FM station more than 80 miles from its source (rough guess). The atmosphere is transparent to FM frequencies (or so I thought) so the signal takes off into outer space. AM can be bent in the fashion described above. Still, if **chrisk** got that Iowa station then who am I to second guess this. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [September 6, 2002, 6:00pm UTC](https://boards.straightdope.com/t/strange-radio-reception/127292/5 "2002-09-06T18:00:32Z")
FM radio uses similar frequencies as TV, but much higher in the radio spectrum than AM radio. AM radio’s signals can bounce back and forth between ionosphere and earth pretty readily, although the total distance traveled is subject to changing factors and the power of the transmitting station. FM radio/TV is nominally line-of-sight, and does not bounce much compared to AM. But it does exhibit atmospheric effects on occasion. Here, north of Green Bay, Wisconsin, I have a tall antenna mounted in a pine tree (it gets taller every year!) which, 80% of the time, picks up Green Bay TV stations very well, but Milwaukee and Chicago ones very little. But last night – perhaps the same night as \*\*chrisk72[/p] observed – the local (50 miles away) Green Bay stations faded out and the Milwaukee (150 miles), Chicago (250 miles) and even Muskegon, Michigan (100 miles) stations came in quite clearly. It’s a good argument to have cable, but that wouldn’t be as exciting. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [September 6, 2002, 6:13pm UTC](https://boards.straightdope.com/t/strange-radio-reception/127292/6 "2002-09-06T18:13:41Z")
> [@](#): > > \*Originally posted by chrisk72 \* > \*\*I live in the Chicago suburbs. Every once in a while, particularly yesterday, my FM radio reception is really strange. I can’t get any local stations clearly, but I can get places like Davenport Iowa, Dearborn Michigan, or less impressive, Madison Wisconsin, clear as a bell instead. Anyone know why? I haven’t seen any correlation with the weather. I know there was a day in August that did the same when it was 98 and humid. Yesterday was 80 and dry. \*\* Supposedly FM radio and other EM signals in that frequency range are unaffected by the Heaviside Layer and so are restricted to line of sight. However, we don’t know everything there is to know just yet and strange things do happen. For instance, over the ocean there is a phenomenon called “ducting.” In this case there is a layer of air that has considerable moisuture as compared to the surrounding air so it has a quite different refractive index. At the junction of the air layers it is possible to get total reflection of a signal and the humid layer acts like a virtual waveguide and radar signals can travel surprising distances following the curvature of the earth. It is possible that in the vicinity of Lake Michigan and with tall buildings around you get weird atmospheric effects and reflections that result in funny propagation anomolies. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [September 6, 2002, 6:58pm UTC](https://boards.straightdope.com/t/strange-radio-reception/127292/7 "2002-09-06T18:58:41Z")
FM can definitely experience skip transmission from the ionosphere, as well as tropospheric ducting. There are a lot of “DX” hobbyists out there with a lot to say about it, like this: [http://www.bext.com/skip.htm](http://www.bext.com/skip.htm) Note: the E layer or E region is a synonym for the Heaviside layer. Summer is a prime time for this, as thunderstorm activity tends to create the right conditions, but as that article notes, it isn’t neccesarily a thunderstorm where you are - so you won’t notice any correlation to your local weather. Chances are good that there is a storm somewhere between you and the unusually distant station you are receiving.