The subject came up yesterday and it got me to wondering. A few years ago, while at home in Florida, My cheapo General Electic clock radio began picking up an FM rock and roll radio station out of Oklahoma City, and the signal came through loud and clear for about an hour before fading out. I was never able to duplicate it.
Florida and Oklahoma are far over the horizon from each other. The only thing I could think of is that the signal was bouncing off some object relaying the signal from the plains to the deep south. Mir? Hubble? The moon? Ionosphere?
What exactly is the straight dope on this phenomenon?
Ham radio operators rely on atmospheric bouncing for long distance communications. You don’t need a satellite.
One other factor is that some radio stations are allowed to boost their signal at night, so their range increases for that reason also. I live in Seattle and can usually get KSL in Salt Lake City at night on my car radio. That’s about 800 miles and definitely over the horizon.
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There is a layer of the ionosphere called the “Heaviside” layer (named after the guy of that name, I think). It is used to “skip” radio signals from long distances. It is because of this layer that AM radio stations turn down their power in the morning.
I find it odd that you got “skip” from an FM station, though; that frequency usually passes right through the Heaviside layer. In general, Heaviside skip peters out at a wavelength of about (rough guess) 50 MHz. Broadcast AM is at about 0.6 to 1.4 MHz, while FM is way up at 88 Mhz.
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Oh, I forgot to mention: the Heaviside layer moves based on the time of day (because of solar ionizing radiation). That’s why the AM stations have to change their power levels in the morning.
Sorry, I should have made that clear.
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There is an entire hobby around picking up radio and TV signals from very far away. Apparently under certain circumstances signals can bounce quite a distance. (This is abnormal propogation. Ham radio operators and short wave stations use ionospheric reflection to bounce signals around the world all the time; it’s when TV and FM stations do it that is unusual.)
I was into the hobby for a while in college then lost interest. My best was the time I picked up TV station CKVR out of Barrie, Ontario crystal clear for about a half hour. I was in central South Carolina at the time using a “rabbit ear” antenna on a portable TV.
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HAARP? Naw, it’s probably the fillings in his teeth.
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Under normal conditions, radio frequencies used by AM (mediumwave) stations are absorbed by the ionosphere during the day, and reflected by night, which is why many stations have to reduce power or sign off at night, to reduce interference. And., again under normal conditions, FM and TV signals completely pass through the ionosphere, day and night, which is why they use the same power, day and night.
However, during periods of high solar intensity (e.g. around noon in the summer), the E-layer of the ionosphere sometimes becomes strong enough to reflect FM and TV signals over tremendous distances. (This is known as “Sporatic E-skip”. Here in North Carolina I have heard an FM station from Maine in stereo on a car radio, and also a Nebraska station on a table radio).
There are also cases where the troposhere can reflect FM and TV signals, which can occur any time of the day and the year, and is most common along the Gulf Coast. A very good review of this topic is at: http://www.anarc.org/wtfda/propagation.htm
About 10 years back, I recieved channel 15 (F0X) from somewhere in Louisiana… it was clear for most of the morning, but then faded into oblivion. I thought it wasn’t bad for a TV that usually has trouble with a signal 30 miles away!
It also picked up a signal 150 miles away Crystal clear during hurricanes. It was a 9 inch JC Penny color TV with analog dials (CLICK-CLICK-CLICK-CLUNK-CLITTER-CLITTER… adjust fine tuning… VIOLA!)
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What you experenced was most likely Tropispheric Ducting ar possibly E layer skip.
This link provides more info on the subject,http://www.wwdx.com/college/
Ham radio operators like myself take great pleasure in useing the various modes of propagation to make contacts at ranges that are not posible under normal conditions.
You might also check out Tha Amature Radio Relay League’s website to learn more about Ham Radio, the URL is http://www.arrl.org
Peace
t lion AKA KC5LNN
Amature Radio Operator Since 1994
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When I was in college, I worked doing some weather research in mountain valleys of Colorado at night. We couldn’t pick up any local radio stations, but we picked up Dr. Ruth’s show from a Los Angeles AM station.
I regularly listen to WFAN 660AM from NYC here in Raleigh, NC, and on a recent drive from Ohio, got it in very clearly all the way from Columbus for the most part - though sometimes a Spanish station overpowers it. I like to think it’s Cuban radio, and I even have a tiny bit of evidence.
A few stations are “Claerchannels,” which means that there are not stations of duplicating frequencies for many miles, and they ar designed to go a long way.
Are these rules still in effect? Or did the glut of radio stations remove them? I seem to recall that WFAN and WABC (770AM NYC) are (were?) clearchannells…
I used to have an antenna that was just a piece of speaker wire strung about 30 feet horizontally across my back yard, and from L.A. I would regularly recieve AM stations from Seattle, Denver and El Paso. San Francisco stations could usually be picked up by a cheap clock radio. San Diego stations play in my fillings.
I live in central California; and one winter night a few years ago I was in the car listening to a crystal-clear AM station. I was baffled by items like the current temperature and news headlines until the announcer identified the station as located in Boise ID. I listened for over an hour, but have never been able to tune that station again.
you may find conditions right to hear a station and never again. depends on the sunspot cycle, time of year, time of day, frequency of the signal, strength of signal, your radio and its antenna position, the station transmitter and its antenna position your and the stations location and what is in between and what you had for dinner.
if you get the same or similar conditions twice then you will hear the station again.