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AM vs. FM Radio Preferences

Radio signals are electromagnetic waves that are sent from a transmitter to oneor more receivers. All electromagnetic waves travel at the speed of light, but

they can have different wavelengths and frequencies. Radio signals occupy certain

ranges of the electromagnetic frequency spectrum.

First of all, there is the AM band of frequencies. These are electromagnetic waves

with frequencies between 535 kHz and 1605 kHz (where a "kHz" represents a kilo

Hertz, or 1000 oscillations per second). The AM (Amplitude Modulation) method

involves the encoding of the original sound through modulating or changing the

amplitude of the radio signal, which is then decoded by the receiver to recover theoriginal sound.

Each AM channel is assigned a range of frequencies, typically about 10 kHz wide. The

common frequency identification (such as AM 1190 for America AM 1190) represents

the midpoint of this operating channel range. Actually, the station uses only about 2.5

kHz on either side of this midpoint because of the interference problems

outside. Therefore, the total bandwidth of an AM channel is typically about 5

kHz. The musical range of the human ear is about 20 kHz, and that is the reason why

AM sounds imperfect.

Theoretically, there can be at most (1605-535)/10 = 107 AM stations in an area. In

practice, the number of AM stations in an area is much lower for a number of other

reasons. AM signals can be reflected from the ionospheric layer back to earth, so that

the signals can reach unintended places that are thousands of miles away. Further, the

ionospheric reflection is increased during the night time. Therefore, the AM signal

from a powerful station in one city can be received in another city, which may be in

another country. For example, when Cuba was attempting to interfere with the

broadcasts of Radio Martí in Florida, their signals were interfering with a radio station

in Iowa. Consequently, AM signals are often subject to regulations such as the use of

directional antennae or reduced power at night time or even going off the air at night.

Then there is the FM band of frequencies. These correspond to electromagnetic waves

with frequencies between 88 mHz and 108 mHz (where a "mHz" represents a million

Hertz, or 1,000,000 oscillations per second). With respect to television signals, the FM

band occupies the spectrum between channels 6 and 7 on the VHF dial. The FM

(Frequency Modulation) method involves the encoding of the original sound through

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modulating or changing the frequency of the radio signal, which is then decoded by the

receiver to recover the original sound.

Each FM channel is assigned a bandwidth of 200 kHz, and the midpoint of this

operating channel range is used for identification purposes (such as Station FM for FM104.1). This means that there can be at most a maximum of (108-88)/0.2 = 100 stations

on the FM dial. The FM bandwidth can easily cover the musical range of the human ear

of about 20 kHz, and that is why FM radio sounds better than AM radio. In fact, the

bandwidth allows FM to be broadcast in stereo.

At the higher frequencies, the FM signals pass unreflected through the ionosphere,

during the day as well as at night. In other words, the FM signals operate by line of

sight. Of course, this limits the coverage area of a FM channel. The size of the

coverage area depends on the height of the transmission antenna, which is oftenlocated at the top of very tall buildings. At the fringe of the coverage area or when

the signal is blocked by landmass or buildings, the FM signal may deteriorate in quality.

The above discourse on the physics of radio engineering serves to bring out these

points:

There is a limit on the number of radio stations that can operate in an area

AM radio has wider coverage than FM radio

FM radio has better sound quality than AM radio

Here we will cite some survey data from the TGI Argentina study. This is a survey of

12,346 persons between 12 and 75 years old conducted by IBOPE Argentina during

1999-2000. These respondents were presented with a list of radio program types and

ask their preferences for either AM or FM reception in listening to each program

type. Each respondent may indicate an preference for AM or FM or indifference. The

survey results are shown in the form of a scatterplot below.

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 (Source: TGI Argentina, IBOPE Argentina)

The scatterplot contains a 45 degree diagonal line. Any radio program type that is

below this diagonal line is preferred more in FM, and any program program type abovethis diagonal line is preferred more in AM. Clearly, the consumers prefer to listen to

music in FM and to spoken words in AM. There are two interpretations of this

phenomenon. First of all, this reflects the strengths of each transmission method ---

larger coverage with theoretically poorer quality for AM, and smaller coverage with

theoretically better quality for FM. Alternately, this simply reflects the fact that AM

stations carry mostly spoken words and FM stations carry most music, each playing to

its own perceived strengths. Thus, the most and the best music programs are found on

the FM spectrum, and the most and the best news programs are found on the AM

spectrum.

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AM vs FM

AM (or Amplitude Modulation) and FM (or Frequency Modulation) are ways of

broadcasting radio signals. Both transmit the information in the form ofelectromagnetic waves. AM works by modulating (varying) the amplitude of the

signal or carrier transmitted according to the information being sent, while the

frequency remains constant. This differs from FM technology in which

information (sound) is encoded by varying the frequency of the wave and the

amplitude is kept constant.

Comparison chartAM FM

Origin: AM method of audio transmission

was first successfully carried out inthe mid 1870s.

FM radio was developed in the

United states mainly by EdwinArmstrong in the 1930s.

Stands

for:

AM stands for Amplitude Modulation FM stands for Frequency

Modulation

Range: AM radio ranges from 535 to 1605kilohertz (OR) Up to 1200 Bits per

second

FM radio ranges in a higherspectrum from 88 to 108

megahertz. (OR) 1200 to 2400 bitsper second

Pros andcons:

AM has poorer sound qualitycompared to FM, but is cheaper and

can be transmitted over longdistances.

FM is less prone to interferencethan AM. However, FM signals are

impacted by physical barriers.