Radio

=The Radio=

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What is Radio? Radio is transmissions of Electromagnetic (EM) waves at very low frequencies. First discovered through mathematics in 1865 by James Clerk Maxwell, the existence of electromagnetic (or radio) waves was tested and confirmed in 1887 by Heinrich Hertz through demonstration in his laboratory. It was found that EM waves are caused by changing magnetic and electric fields that self propagate through space. Radio waves themselves are caused by the acceleration of a charged particle whose frequency falls within the designated ‘RF’ range (see list of Radio Frequencies). Common forms of radio waves are AM and FM waves. Since Nikola Tesla and Guglielmo Marconi discovered their great potential for communication, radio waves have been at the core of the modern worlds global communication system. The two main applications of radio waves in telecommunication are radio and television.

Dubbed 'Broadcast' frequencies, the United states uses the follow frequencies to transmit information to the masses:
 * Longwave AM Radio = 148.5 - 283.5 kHz (LF)
 * Mediumwave AM Radio = 530 kHz - 1710 kHz (MF)
 * Shortwave AM Radio = 3 MHz - 30 MHz (HF)
 * TV Band I (Channels 2 - 6) = 54 MHz - 88 MHz (VHF)
 * FM Radio Band II = 88 MHz - 108 MHz (VHF)
 * TV Band III (Channels 7 - 13) = 174 MHz - 216 MHz (VHF)
 * TV Bands IV & V (Channels 14 - 69) = 470 MHz - 806 MHz (UHF)

__**How Does Radio Work?**__ Radio Signals are made up of the frequencies listed above, and the bands of those frequencies are called __channels__. The widths of these channels determine the amount of information that can be sent on one. This being said, a higher data rate needs a wider channel than a lower data rate. The FCC regulates what channel widths and sometimes even what type of __modulation__ is used. For radio signals to work, there are two essential parts of the sending process, the transmitter and the reciever. Lets break this down into to parts:



__**Modulator:**__ The Modulator controls the part of the wave that is changed to reflect the data being transfered (also called keying). Usually, phase shift, amplitude, and frequency are changed to represent data. Today, because of FCC resolutions and more recent discoveries, the most common form of modulation is Gaussian Frequency Shift Keying (GFSK) as shown below. Where Fc is the Carrier Frequency(also assigned by the FCC), and each Gaussian roll off represents the subsequent additions of the response frequency, or FR (which is also, coincidentally, the bit rate of the data). The main lobe of the graph has a bitrate that is 2 x FR.

__**The Filter:**__ Because of FCC regulations, radio transmitters are restricted to certain broadcast "Bandwidths." This is a literal term that is defined by the width of the wave segments allowed to pass. The Filter is a stage in the transmission process that determines what part of the signal constitutes the wave and band. The two graps in the figure below are two common types of filters, the Band Pass and the Band Stop. They are simply inverted graphs, one with the band of information being concave down (Pass) and the other being concave up (Stop). The third graph is a graph of the actual signal, plotted on an attenuation(dB) v. frequency graph. The attenuation bands are the widths between pulses of the wave, and the bandwidth, the part that is designated due to regulation, is the width of the pulse.

RF Power is measured in watts or milliwatts (W or mW, respectively). Since the power at the transmitter and reciever are normally so far apart, the logarithmic decibel scale is used. Normally, P2 is a specified values, so the equation becomes: Where PdBm is in in dBm and PmW is in mW.
 * __Radio Frequency Power__**

As shown in the graph, there is a required minimum power. This is also to prevent interference on Class A, B, and C devices as allotted by the FCC. This minimum power prevents receivers from picking up external noise from other devices and allows the broadcast to remain much more secure, the idea of the regulatory designations.

Some common values for low-power bands include:
 * 1mW = 0dBm = -30dBW
 * 10mW = 10dBm = -20dBW
 * 50mW = 17dBm = -13dBW
 * 100mW = 20dBm = -10dBW
 * 200mW = 23dBm = -7dBW
 * 1000mW = 1W = 30dBm = 0dBW

The Thermal noise in a transmitter needs to be below a certain level in order to comply with the FCC interference regulations. This noise is calculated by technicians by using the Boltzmann Equation:
 * __Thermal Noise__**



Where:
 * N - Thermal Noise Power
 * B - Bandwidth in Hertz
 * T - Temperature in Kelvin
 * k - Boltzmann's constant (1.38E-23 Joules/Kelvin).