What do radio station numbers mean

This may explain why your favorite AM radio station goes off the air at sunset, or becomes much harder to hear because of reduced power. For starters, they are on a higher frequency in the RF spectrum The name RF , stands for radio frequency, but when TV came along they just stuck with the name. T he FM radio band goes from 88 to MHz megahertz, or millions of cycles per second. Again, you can see these numbers on your FM radio dial. To keep from interfering with each other FM stations must be KHz apart within the same geographic area.

However, since the signals of FM stations cover only limited distances, the same frequencies can be used in different geographic areas of the country. Unlike AM radio stations, FM stations, at least in the United States, don't end up being assigned frequencies with nice round numbers like or Thus, an FM station may be at Y ou may have noticed that FM or TV stations don't reduce power or sign off the air at sunset.

Because of their higher frequency ionospheric refraction doesn't appreciably affect FM or TV signals. F or the most part, FM and TV signals are line-of-sight. Although this means that FM stations don't interfere with each other, this characteristic creates a couple of other problems.

First, these waves go in a straight line and don't bend around the earth as AM ground waves do. Thus, they can quickly disappear into space. Note that the earth is round — we hope this doesn't come as a shock to anyone — and, therefore, these signals will literally leave the earth after 75 miles or so.

And, there's another problem. Since FM and TV signals are line-of-sight, they can be stopped or reflected by things like mountains and buildings.

In the case of solid objects like buildings, reflections create ghost images in TV pictures and that "swishing sound" when you listen to FM radio while driving around tall structures. O f course, the higher the FM or TV transmitter antennas are the greater area they will cover — which explains why these antennas are commonly very tall, or placed on the top of mountains. AM radio doesn't need that kind of advantage, since, as we've seen, AM radio waves don't behave in the same way.

This band of the radio spectrum is used for no other purpose but FM radio broadcasts. In the same way, AM radio is confined to a band from kilohertz to 1, kilohertz kilo meaning "thousands," so , to 1,, cycles per second.

On the next page, learn more about about frequency bands and the frequencies that common gadgets use. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. This article will explain what they are, how to listen to them, and why they matter. Cryptography, the science of encrypting text and data, has been around since the times of Caesar.

Before the invention of radio, secret messages could be conveyed in coded letters or through light signals. In the 19th century, transmission along electric lines became possible, first with the telegraph and then with the telephone. The first use of coded numbers broadcasts was during the last years of World War I, when they were sent in Morse code in Low and Medium wave frequencies.

Shortwave came into use in the early s and has been used to send encrypted messages since then. When directed at the ionosphere at an angle, shortwave signals reflect back down to Earth at great distances beyond the horizon.

This is handy for intelligence operations in foreign countries, or for the military to send orders to faraway units. But if these signals can be heard all over the world, then, of course, the messages must be encrypted. This is where one-time pads come in.

The one-time pad , the only mathematically unbreakable encryption system, is usually a sheet of paper with random numbers in groups of five or more digits. This is sometimes possible for counterintelligence, either using double agents or by arresting the recipient, most likely while he is receiving the signal.

A number of events in the 20th century have proven that intelligence agencies do, in fact, use these signals. Most were captured with their radio transmitters and code books. The mono signal combined left and right leaves the transmitter as a single signal.

In addition to stereo, FM benefits from having a wider bandwidth than AM, kilohertz vs 10 kilohertz. This wider bandwidth give FM a frequency response that extends from below 10 Hertz to 15, Hertz. As a result the listener hears a truer representation of sound. Most music formats are now heard on FM. Talk and news, formats popular on AM are also heard on FM.

One of FM's other major advantages is a built in resistance to interference. Unlike AM, FM transmission varies the frequency of the signal keeping the amplitude constant. Static interacts with the amplitude of radio waves. FM does have disadvantages with respect to AM.

It occupies the VHF band. Signals at these higher frequencies attenuate quickly and travel line-of-sight , no further than the horizon. FM signals are also prone to multipath interference.

This happens when a bounced signal interacts with the original signal inside your receiver. One of the most important things to learn about radio is that not all stations are created equal.

According to radio consultant Jay Williams, Jr. AM Stations AM stations are those broadcast stations that occupy the portion of the broadcast spectrum between khz - khz. A clear channel is one on which stations are assigned to serve wide areas.

These stations are protected from objectionable interference within their primary service areas and, depending on the class of station, their secondary service areas.

Stations operating on these channels are classified as follows: 1 Class A station. A Class A station is an unlimited time station that operates on a clear channel and is designed to render primary and secondary service over an extended area and at relatively long distances from its transmitter.

Its primary service area is protected from objectionable interference from other stations on the same and adjacent channels, and its secondary service area is protected from interference from other stations on the same channel.