Friday, April 8, 2016

Long-Distance AM Radio Reception At Risk?

AM radio stations, particularly powerful stations, often transmit hundreds of miles at night due to "Sky-Wave" radio propagation, where the radio signal bounces off of the ionosphere portion of the Earth's atmosphere. (Image Source: )

By Glenn A. Walsh
Reporting for SpaceWatchtower

Since 1920 November 2, with the first broadcast of the world's first commercial radio station, KDKA-AM in Pittsburgh (although, the very first broadcast came from atop the Westinghouse plant in the suburb of East Pittsburgh), many AM radio stations have been heard hundreds of miles from their transmitters at night.

However, the U.S. Federal Communications Commission (FCC) has proposed new rules which could cause great interference to the many powerful radio stations that broadcast for hundreds of miles between sunset and sunrise. The FCC proposes to allow other radio stations with lower powers, on the same or adjacent frequencies to the powerful stations, be allowed to increase their time of operation (i.e. allow these stations to operate between sunset and sunrise) and / or increase their transmission power level. This will increase interference to the more powerful stations, making it more difficult for the more powerful stations to be heard hundreds of miles away.

Normally, during daytime hours, AM radio signals use “Ground-Wave” radio propagation, whereby the ground is used to propagate the radio signal. For most AM radio stations, which are only licensed to use 5,000 watts of power or less, these radio stations are heard only within a 30 to 50 mile radius. The most powerful 50,000 watt AM radio stations can be heard within a hundred miles or further in the daytime.

Between sunset and sunrise, AM radio stations, particularly the most powerful, 50,000 watt radio stations, can be heard hundreds of miles from the radio station transmitter, due to, what is known as, “Sky-Wave” or “skip” radio propagation. Instead of just hugging the ground, radio waves also reflect off of a portion of the atmosphere called the ionosphere, back to the Earth hundreds of miles from the transmitter.

The ionosphere exists about 50 to 620 miles / 80 to 1000 kilometers above the Earth's surface. In the ionosphere, air is ionized by photons from the Sun and by cosmic rays. Ionospheric conditions can be disrupted by solar flares, particularly during times of high sunspot activity. Then, long-distance radio propagation can be degraded, and in some rare instances, enhanced.

The lower levels of the ionosphere largely disappear at night (and sometimes, very briefly, during a daytime Solar Eclipse), when not being bombarded by solar radiation. Hence, the refractive layer of the ionosphere is much higher allowing AM radio waves to be reflected back to the Earth hundreds of miles away.

Higher frequency radio signals, including those of FM radio stations and television stations, cannot, normally, use “Sky-Wave” radio propagation. These signals, which normally do not bounce off of the ionosphere back to the ground, completely penetrate the ionosphere and continue into Outer Space; although, under extreme ionization conditions, sometimes these stations can also be heard hundreds of miles away. These stations are normally received, generally, within the "line-of-sight" of the transmitter.

Short-wave radio stations, particularly, take advantage of “Sky-Wave” transmissions. At short-wave frequencies, radio transmissions can be heard thousands of miles away. In extreme ionization events, sometimes AM radio stations can, also, be heard at such distances.

At the dawn of commercial radio broadcasting, AM radio stations were mostly built in the larger cities of the country, with very few stations existing in rural areas or the mountainous areas, particularly in the west. So, the FCC (originally known as the FRC, Federal Radio Commission) created a special class of radio station, which was originally called a “Clear-Channel” station. The FCC had allocated a “Clear-Channel” radio frequency to have only one, or sometimes two, radio stations operating on that particular frequency from sunset to sunrise. In the case of a "Clear-Channel" with two nighttime stations, usually one would broadcast from the East Coast while the other broadcast from the West Coast; this distance seemed far enough away to minimize interference.

At night, such "Clear-Channel" stations would have virtually no interference from other stations on their frequency. All other radio stations operating on that particular “Clear-Channel” radio frequency were required to sign-off and leave the air at sunset, and not return to the air until sunrise.

So, using “Sky-Wave” transmissions, at night nearly every inch of American soil could be served by one or more of these "Clear-Channel" stations. This allowed thousands of Americans, who had no radio station to listen to during the daylight hours, an opportunity at night to get up-to-the-minute news, weather forecasts, and information particularly of interest to farmers.

Today, most major cities in this country have one or two, and sometimes more, very powerful AM radio stations, which can be heard hundreds of miles from their transmitters at night. In addition to Pittsburgh's KDKA, some of the better known of these AM radio stations include WWVA in Wheeling, WWKB in Buffalo, WHAS in Louisville, WGY in Schenectady, WTIC in Hartford, WBZ in Boston, WBAL in Baltimore, WRVA in Richmond, WSB in Atlanta, WCCO in Minneapolis, KMOX in St. Louis, WWL in New Orleans, WBAP in Ft. Worth, KOA in Denver, and KSL in Salt Lake City.

Some cities have several such powerful stations including WCBS, WBBR, WABC, and WOR in New York City; KYW and WPHT in Philadelphia; WLW and WCKY in Cincinnati; WSM and WLAC in Nashville; WBBM, WSCR, and WGN in Chicago; KNBR and KGO in San Francisco; and KNX and KFI in Los Angeles.

With 50,000 watts of transmitting power (the highest power level allowed for AM radio stations in the United States), the stations originally known as “Clear-Channel” radio stations are now classified as “Class A” radio stations by the FCC. Over the years, the FCC has allowed some lower-power stations, which operate on a "Clear-Channel" but are not Class A stations, to stay on later at night or start broadcasting earlier in the morning (at a power level lower than their normal daytime power level), so long as these stations do not interfere with the more powerful “Clear-Channel” stations.

Now, the FCC wants to eliminate all rules that forbid interference with Class A radio stations, by other radio stations on the same or adjacent frequencies. Over the last few years, the FCC has solicited public comments on this proposal. Final public comments were due last month.

Former radio station General Manager Glenn A. Walsh submitted public comments last month opposing the FCC plan. According to Mr. Walsh, "The major advantage of AM radio is long-distance broadcasting. If you create more interference for stations which have been successfully providing a good long-distance service for nearly a century, you are degrading the most valuable aspect of AM radio!"

In his public comments, Mr. Walsh added, "If your goal is more and better local radio stations, it would be far better to increase the size of the FM radio band, which provides the best local service and cannot provide a long-distance service."

In the 1970s, Mr. Walsh served as General Manager of a small, educational radio station near White Sulphur Springs, West Virginia, WLCR-AM Carrier Current, at a Summer camp for boys and girls called Camp Shaw-Mi-Del-Eca. Mr. Walsh taught the campers radio theory and radio station operation, and several of the campers went-on to acquire a FCC Third Class Commercial Radiotelephone License with Broadcast Endorsement.

Public Comments to the FCC from Glenn A. Walsh, regarding the proposed elimination of rules preventing interference to Class A radio stations:
Link >>>;ECFSSESSION=4n8PWxTQ6WJZ2L2h92R0nNJ5V5Q1XfwLSKlqPSvrx1RxY3v6Dnqb!634993814!-322446565?id=60001513703

More on Sky-Wave Radio Propagation: Link >>>

More on Clear-Channel AM Radio Stations, including a List of All Clear-Channel Stations:
Link >>>

More on Educational Radio Station WLCR-AM Carrier Current, near White Sulphur Springs, West Virginia: Link >>>

2015: 95th Anniversary of the World's First Commercial Radio Station, KDKA-AM in Pittsburgh:
Link >>>

Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Friends of the Zeiss.
              2016 April 8.

                                                               Historic 10-inch Siderostat-type Refractor Telescope at Pittsburgh's original Buhl Planetarium and Institute of Popular Science.
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