Basic Differences Between AM and FM

We need to mention a couple of other things before we leave the discussion of how radio works.  We’ve talked about AM and FM radio, but we haven’t explained the real difference.

In fact, there is a lot of difference — and not just a difference in the station numbers on your radio dial.

The first type of radio service — the one we’ve been talking about in the last couple of modules — was AM radio.

The term modulation refers to how sound is encoded on a radio wave called a carrier wave; or, more accurately, how the sound affects the carrier wave so that the original sound can later be detected by a radio receiver.

In the top-left of this drawing the RF energy (carrier wave) is not modulated by any sound.  There would be silence on your radio receiver.

Sound transmitted by an AM radio station affects the carrier wave by changing the amplitude (height) of the carrier wave, as shown on the left.

Unfortunately, this type of modulation is subject to static interference from such things as household appliances — and especially from lightening storms.

AM also limits the loud-to-soft range of sounds that can be reproduced (called dynamic range) and the high-to-low sound frequency range (called frequency response, to be explained below).

FM radio, which came along in the 1930s, uses a different approach than AM. It’s virtually immune to any type of external interference, it has a greater dynamic range, and it can handle sounds of higher and lower frequencies. This is why music, with its much greater frequency range than the human voice, sounds better on FM radio.

Note on the left that when the carrier wave of FM radio is modulated with sound that the distance between the waves, or the frequency of the carrier wave, changes.

Thus, AM radio works by changing the amplitude of the carrier wave and FM radio works by changing the frequency of the carrier wave.

Frequency Response

Frequency relates to the basic pitch of a sound — how high or low it is. A frequency of 20 Hz would sound like an extremely low-pitched note on a pipe organ — almost a rumble.

At the other end of the scale, 20,000 Hz would be the highest pitched sound that can be imagined, even higher than the highest note on a violin or piccolo.

As we’ve noted, frequency is measured in Hertz (Hz) or cycles per second (CPS). A person with exceptionally good hearing will be able to hear sounds from 20-20,000 Hz.

Since both ends of the 20-20,000Hz range represent rather extreme limits, the more common range used for FM radio and TV is from 50 to 15,000 Hz. (A typical AM radio signal does not cover this entire range.)

Although the 50-15,000 Hz doesn’t quite cover the full range that can be heard by people with good hearing, it covers almost all naturally occurring sounds.  Note in the drawing above that the ear does not hear all frequencies of sound at the same loudness, but a good microphone does.

The sound level or amplitude of sound in radio and TV stations is monitored and adjusted with the help of a volume units meter (VU meter) meter. One model is shown on the left.  Audio levels must be carefully controlled in broadcasting to keep noise and distortion from reducing the quality of sound.

About Electromagnetic Pulse

Electromagnetic Pulse (EMP) is an instantaneous, intense energy field that can overload or disrupt at a

distance numerous electrical systems and high technology microcircuits, which are especially sensitive to power surges.  A large scale EMP effect can be produced by a single nuclear explosion detonated high in the atmosphere.  This method is referred to as High-Altitude EMP (HEMP).  A similar,smaller-scale EMP effect can be created using non-nuclear devices with powerful batteries or reactive chemicals.  This method is called High Power Microwave (HPM).  Several nations, including reported sponsors of terrorism, may currently have a capability to use EMP as a weapon for cyber warfare or cyber terrorism to disrupt communications and other parts of the U.S. critical infrastructure.  Also, some equipment and weapons used by the U.S. military may be vulnerable to the effects of EMP.

 The threat of an EMP attack against the United States is hard to assess, but some observers indicate that it is growing along with worldwide access to newer technologies and the proliferation of nuclear weapons.  In the past, the threat of mutually assured destruction provided a lasting deterrent against the exchange of multiple high-yield nuclear warheads.  However, now even a single, low-yield nuclear explosion high above the United States, or over a battlefield, can produce a large-scale EMP effect that could result in a widespread loss of electronics, but no direct fatalities, and may not necessarily evoke a large nuclear retaliatory strike by the U.S. military. This, coupled with published articles discussing the vulnerability of U.S. critical infrastructure control systems, and some U.S. military battlefield systems to the effects of EMP, may create a new incentive for other countries to rapidly develop or acquire a nuclear capability. Policy issues raised by this threat include (1) what is the United States doing to protect civilian critical infrastructure systems against the threat of EMP, (2) could the U.S. military be affected if an EMP attack is directed against the U.S. civilian infrastructure, (3) are other nations now encouraged by U.S. vulnerabilities to develop or acquire nuclear weapons, and (4) how likely are terrorist organizations to launch a smaller-scale EMP attack against the United States ?

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Mobile telephone radio wave effects

Like all other radio communication applications, mobile telephony uses radio waves to carry the information, like voice, text and images, through the air. Radio waves are a kind of electromagnetic fields (EMF) that are also called radio frequency fields or radio frequency energy. Electromagnetic fields are present in our every day life, both naturally and from man-made sources. Radio waves travel with the speed of light. They consist of an electric and a magnetic component, which vary periodically in time. The number of oscillations per second is called the frequency. The intensity of the radio waves is normally expressed as power density, and sometimes also as electric and magnetic field strength. The radio wave intensity is dependent on the distance to the transmitter, for example a mobile phone or a base station antenna, and to the output power of the transmitter. The lower the power and the longer the distance, then the lower the intensity will be.

Different types of electromagnetic fields have different frequencies. Visible light, for instance, has higher frequencies than radio waves, but lower than ultraviolet light. Electromagnetic waves with frequencies higher than ultraviolet light are called ionizing radiation, which has sufficient energy to break molecular bonds and thereby the potential to cause damage to biological tissue. X-rays and gamma rays are examples of ionizing radiation. Radio waves belong to the lower frequency part of the electromagnetic spectrum, which is called non-ionizing radiation. Here the electromagnetic energy is too low to break molecular bonds.

When a person is exposed to the radio waves from mobile phones or base stations, most of the energy will be reflected by the body or travel around it (called diffraction). Some of the energy will however be absorbed in the tissues at the surface of the body. Inside the body certain molecules, like water, will start to move or rotate due to the presence of the electromagnetic fields. By “friction” the energy is converted into heat. If the radio wave intensity is very high, the heating may be significant and potentially detrimental. The power used by mobile phones is very low and the tissue heating due to radio wave absorption is too small to be noticeable. The specific absorption rate, SAR, is used to specify the amount of radio frequency energy absorbed in the body. SAR is expressed in the unit watts per kilogram (W/kg).

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Radio, a potential medium for education

While admiring the growth of radio production and broadcast technology, Madhu Ranjan feels that it still continues to be an under-utilized technology in education. According to her, radio has enormous potential to improve distance education systems especially when integrated with other technologies such as television, mobile telephones, and the Internet.

Soon after its invention in the late 1890s, radio, due to its information and

entertainment value, vast reach, and immediacy, became the most popular means of mass communication around the world.

With the arrival of television, the birth of satellite broadcasting technology, and later the Internet, radio’s listener base began to erode and its importance diminished.  In the 1970s, however, radio (FM band) once again gained popularity, especially among young listeners.

Today, improved broadcasting quality, more innovative and entertaining content, and new technological developments in fields such as digital and satellite radio have made radio a resurgent medium, extremely popular in the fields of advertising and entertainment. Affordability, portability, and access indoors and outdoors give radio a clear edge over other media. Additionally, radio is increasingly becoming a more dynamic medium, as it is integrated into other new technologies such as television, mobile telephones, and the Internet.

This has opened up new opportunities for a variety of forms of delivery and access. For example, portable, low-cost FM transmitting stations have been developed and digital radio systems that transmit via satellite are being set up in many parts of the world. Internet streaming audio software technology now allows a global audience to listen to news from a distant country. In addition, the development of wind-up and solar radios utilizing inexpensive power sources allows radio to can cut across geographic, economic, and cultural boundaries.

However, radio still continues to be an under-utilized technology in education. This is somewhat surprising because, for a learner, radio is a simple, user friendly, accessible, and a well-established medium. From an educational provider’s point of view it is easy and inexpensive to set up, produce, and broadcast programs. Most nations currently have the engineering skills and broadcasting talent to apply this technology to education.

Today, many schools, colleges, universities, and other organizations use distance education systems. While developing a distance education system, factors such as cost effectiveness, efficiency, and the availability of appropriate communication technologies, as well as access and equity issues, particularly those related to gender, language, social status, and religion, are the most important considerations.

Other factors to consider relate to how distance learners can best use their higher order thinking skills and how they can cope with the limitations of time, age, gender, and language. Radio is able to address these issues while reaching a diverse group of learners and can be valuable in many different distance learning environments including schools, colleges and universities, businesses, and public sector organizations.

For distance education providers, radio is a cheaper alternative to other communication technology mediums. Producing interactive radio programs in distance education requires only low-priced equipment compared with other cutting-edge technologies. Educational institutions do not need to spend much money for establishing interactive radio studios in their organizations.

Learners are equally fortunate, because they do not have to buy or rent the costly and complex equipment required by TV and the Internet. There are no boundaries to broadcasting educational programs with interactive radio throughout the world and as long as learners have access to a very low-cost radio, they can listen to programs wherever they are; riding in their cars, traveling by bus or train, or working at home.

Moreover, interactive distance educational programs can be recorded for learners via inexpensive equipment, such as cassettes, CDs, or MP3 players. Educational radio helps provide equal access to knowledge for everyone by breaking digital walls around the world.

Interactive radio programs allow people with disabilities (with the exception of the hearing-impaired) to hear the voices of instructors, classmates, and experts, enhancing their ability to learn. While listening to interactive radio programs, learners have more time to construct knowledge.

Community radio is also an immensely powerful technology for the delivery of information with enormous global potential.  It is particularly powerful in providing access to information for marginalized populations, including women, minorities, and the poor, who often do not have access to more cutting edge technology. Radio can expand opportunities for the intended beneficiaries of development to participate in the in the development agenda, which can appropriately and adequately respond to their needs and aspirations.

Currently, the benefits of radio as a learning medium are overlooked. Conventional wisdom assumes that high-cost communication media ensure better interactive distance learning. Radio, however, when incorporated with interactive learning approaches, has enormous potential to improve distance education systems. In a very imaginatively designed program – funded by USAID and implemented by EDC – that makes the process of teaching-learning interesting and meaningful, radio lessons that introduce substantial interaction among students and teachers are improving classroom interaction in close to 300,000 government schools reaching over 25 million primary school students across several states in India.

Many interventions around the world are using radio innovatively; successfully enhancing the quality of teaching learning in traditional classroom settings, imparting health messages to communities; and providing useful information on agriculture to farmers.  Although it is not currently being exploited to its full potential, radio is a medium with tremendous potential, particularly for educational purposes. Get payday advance service for easy payment