8/2/2019 Notes 4th Sem
1/1
The Difference Between AM and FM
AM and FM are two very popular and very different methods of
sending information
over the airwaves. AM is amplitude modulation while FM is
frequency modulation.
But what is modulation? It is the act of modifying a certain
aspect of the carrier
frequency in accordance to the information being sent. It is
then clear that AMmodifies the amplitude of the carrier frequency
while FM modifies its frequency.
AM is the older an easier of the two technologies to implement.
The receiver detects the changes in the
carrier frequencys amplitude and amplifies it to drive a
speaker. The simplicity of the technology made it
easy to build radio receivers in great quantities. The main
problem associated with AM broadcasting is
the fact that it is very susceptible to various weather
conditions that deteriorate and distort the signal. The
simplicity of the design also limits the broadcast to a single
audio channel, making it inadequate for stereo
sound.
FM is a development over AM broadcasting and it provides a lot
of substantial
benefits thus it is much more complex compared to AM. The first
and mostsubstantial benefit is its ability to send out two channels
of information at the same
time with the use of advanced algorithms. This allows the
station to broadcast left and
right audio channels for full stereo sound. Since most
environmental factors that
distort radio waves only affect its amplitude and not the
frequency where FM stores
the actual voice signal, the data in the FM signal doesnt
degrade as easily as AM.This also means that FM signal quality
doesnt degrade linearly as you get further
from the transmitting station.
Range wise, AM takes the cake with its much greater distance
travelled. FM signals
usually drop of at around 50 miles from the station, but AM
waves can be refracted inthe atmosphere resulting in greater range.
The range is also one of the reasons why
talk radio prefers AM even if the sound quality is not very
high.The advancement in
technology also meant that the degree in complexity and price
between AM and FM
receivers have become moot. Most manufacturers can even manage
to place the whole
circuitry for both AM and FM inside a single chip, turning them
into a package
instead of competing against each other.
Summary:
1. AM broadcasting is simpler than FM but the difference in
complexity and price are
very marginal at present.
2. AM is more prone to signal distortion and degradation
compared to FM.
3. FM doesnt degrade linearly with distance.
4. AM usually broadcasts in mono which makes it sufficient for
talk radio.
5. FM can transmit in stereo making it ideal for music.
6. AM has a longer range than FM.
