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<a href="http://www.fas.org/man/dod-101/navy/docs/es310/syllabus.htm"><img src="FM2_files/up.gif"> Introduction to
Naval Weapons Engineering</a><br><hr>
<h1><center>Frequency Modulation</center></h1>
<hr>
<h3><a href="#obj">Objectives</a></h3>
<h3><a href="#basic">Basic System</a></h3>
<h3><a href="#mod">Modulation</a></h3>
<h3><a href="#fm">FM</a></h3>
<h3><a href="#spect">FM Spectrum</a></h3>
<h3><a href="#perf">FM Performance: </a> <a href="#bw">Bandwidth </a>,<a href="#eff">Efficiency </a>,
and <a href="#noise">Noise</a></h3>
<h3><a href="#summ">Summary</a></h3>
<hr>
<h2><a name="obj">Objectives</a></h2>
<ol>
<li>Know the relationship of carrier frequency, modulation frequency
and modulation index to efficiency and bandwidth
</li><li>Compare FM systems to AM systems with regard to efficiency,
bandwidth and noise.
</li></ol>
<h2><a name="basic">Basic System</a></h2>
<p>
The basic communications system has:
</p><dl>
<dt>Transmitter: <dfn>The sub-system that takes the information
signal and processes it prior to transmission. The transmitter
modulates the information onto a carrier signal, amplifies the
signal and broadcasts it over the channel</dfn>
</dt><dt>Channel:<dfn> The medium which transports the modulated signal
to the receiver. Air acts as the channel for broadcasts like radio.
May also be a wiring system like cable TV or the Internet. </dfn>
</dt><dt>Receiver: <dfn>The sub-system that takes in the transmitted
signal from the channel and processes it to retrieve the information
signal. The receiver must be able to discriminate the signal from
other signals which may using the same channel (called tuning),
amplify the signal for processing and demodulate (remove the carrier)
to retrieve the information. It also then processes the information
for reception (for example, broadcast on a loudspeaker).</dfn>
</dt></dl>
<p>
<img src="FM2_files/IMG00029.GIF"> <br>
</p><h2><a name="mod">Modulation</a></h2>
<p>
The information signal can rarely be transmitted as is, it must
be processed. In order to use electromagnetic transmission, it
must first be converted from audio into an electric signal. The
conversion is accomplished by a <i>transducer</i>. After conversion
it is used to modulate a carrier signal.
</p><p>
A carrier signal is used for two reasons:
</p><ul>
<li>To reduce the wavelength for efficient transmission and reception
(the optimum antenna size is ⌨️ 快捷键说明
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