Week 1 Assignment

Please answer the following questions, you can upload your answers in a MS Word file, or Word file. Answer all the questions, and upload the answers back before Sunday March 31, 2013 (before 11: 55 pm): 1. Differentiate between guided media and unguided media 2. What are three important characteristics of a periodic signal 3. Define funamental frequency 4. What is attenuation? 5. Describe the components of optical fiber cable. 6. Indicate some significant differences between broadcast radio and microwave. 7. What is the difference between diffraction and scattering? . List and briefly define important factors that can be used in evaluating or comparing the various digitial-to-digital encoding techniques. 9. What function doeas a modem perform? 10. What is QAM? Differentiate between guided media and unguided media Guide media is that where we use any path for communication like cables (coaxial, fiber optic, twisted pair) etc. Unguided media is also called wireless where not any physical path is used for transmission. What are three important characteristics of a periodic signal?

Period (or frequency), amplitude and phase. All periodic signals can be broken down into other signals… most commonly sine/cosine waves, but there are others too. These components will each have their own frequency, amplitude and phase that combine into the original signal. The strange part of the question is the phase. A signal on its own does not have a phase unless you provide some reference signal to compare it to. Generally, this comparison signal is implied by the context of your particular situation.

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When you decompose a periodic signal into components, however, it is almost always implied that the phase of each component is in reference to the fundamental component (So the fundamental has phase 0, while the others have phases referenced to that). This is done specifically so that each component will combine to create the original signal. Define fundamental frequency. What is attenuation? The fundamental frequency, often referred to simply as the fundamental, is defined as the lowest frequency of a periodic waveform.

In terms of a superposition of sinusoids The fundamental frequency is the lowest frequency sinusoidal in the sum. In some contexts, the fundamental is usually abbreviated as f0 (or FF), indicating the lowest frequency counting from zero. [1][2][3] In other contexts, it is more common to abbreviate it as f1, the first harmonic. [4][5][6][7][8] (The second harmonic is then f2 = 2? f1, etc. In this context, the zeros harmonic would be 0 Hz. )All sinusoidal and many non-sinusoidal waveforms are periodic, which is to say they repeat exactly over time.

A single period is thus the smallest repeating unit of a signal, and one period describes the signal completely. We can show a waveform is periodic by finding some period T for which the following equation is true: Reduction of signal strength during transmission. Attenuation is the opposite of amplification, and is normal when a signal is sent from one point to another. Describe the components of optical fiber cable. An optical fiber is a flexible, transparent fiber made of glass (silica) or plastic, slightly thicker than a human hair.

It functions as a waveguide, or “light pipe”, to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication. Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference.

Fibers are also used for illumination, and are wrapped in bundles so that they may be used to carry images, thus allowing viewing in confined spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers. Indicate some significant differences between broadcast radio and microwave. VLF Radio is about 50 Kilohertz to 400 Kilohertz. AM Broadcast Band Radio is about 500 Kilohertz to 1600 Kilohertz. And microwave begins around 2000 MHz and goes up thru. Some frequency ranges like 26,000 MHz in allocated bands, depending upon the type of service you’re operating.

What is the difference between diffraction and scattering? Diffraction is a phenomenon observed only in waves, but scattering is a phenomenon observed in both waves and particles. Diffraction is a property of propagation of waves, whereas scattering is a property of wave interactions. Diffraction can be taken as evidence for the wave nature of light. Some forms of scattering (Compton scattering) can be taken as evidence for the particle nature of light. List and briefly define important factors that can be used in evaluating or comparing the various digital-to-digital encoding techniques.

Digital signals don’t have large ranges, nor do they reflect constant activity. Digital signals have very few values. Each signal is unique from a previous digital value and unique from one to come. In effect, a digital signal is a snapshot of a condition and does not represent continual movement In comparing analog and digital signals, advantages lie on either end of the spectrum. Analog signals suffer far less from attenuation over long distances. This rather makes sense. Since digital data can only be a 1 or 0, what happens when a signal becomes so weak that it is hard to distinguish between each state? Sometimes we just can’t.

Analog devices, on the other hand, are equipped to handle the infinite values between 1 and 0. Digital devices are a lot less sophisticated, meaning that they are fairly easy to manufacture and cost-effective. In addition, digital devices are more resilient to EMI and make more efficient use of the cabling bandwidths than analog systems do. What function does a modem perform? The function of a modem is Modulation and Demodulation mean to turn data into a format that can be transmitted via an audio link such as a phone line. A modem at the other side of the connection answers the phone and converts the audio back into usable data.

This is why if you lift a phone while the modem is in use there appears to be random noise on the line, this noise is the data in audio What is QAM? QAM stands for Quadrature Amplitude Modulation. It’s a modulation scheme that transmits data by changing the amplitude of two carrier waves. The two carrier waves are out of phase with each other by 90 degrees. Digital Cable uses QAM to transmit the majority of their signals. Two major QAM schemes are 64QAM and 256QAM. 64QAM contains data throughput around 28 mbps, where 256QAM has data throughput of 38. 8 mbps.