hw1 - University of California, Berkeley EECS 142 Fall 2011...

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University of California, Berkeley Fall 2011 EECS 142 Prof. A. Niknejad Problem Set 1 Due Thursday September 6, 2011 Answer the following questions to the best of your ability. Use any resource (such as texbooks or the Internet/Wikipedia) to answer these questions. Feel free to ask the GSI or instructor for help. 1. Many simple antennas, such as a dipole, are most efficient when they are a significant fraction of the wavelength (quarter or half). (a) For operation at 900 MHz, what is the half-wave dipole length? (b) At 2.4 GHz? (c) At 10 MHz? (d) Explain the choice of carrier frequency based on this information for portable wireless devices. (e) (Bonus) What is the downside of a very short antenna ( ± λ )? 2. (a) What determines the minimum detectable signal for a receiver? ( Hint : What do you hear on a radio when it’s tuned to a channel without a station?) (b) What determines the largest signal? ( Hint: Consider an audio amplifier that is driven with a signal that is too large for it to handle? Radio receivers also employ amplifiers that exhibit the same behavior.) 3. (a) What’s the typical received signal strength of a cellular phone? (b) What voltage does that impart onto the antenna? (c) How about for WLAN (Wi-Fi)? (Hint: Use the signal strength indicator of your WLAN utility or a program such as iStumbler on a Mac.) 4. (a) What is the typical loss of a coaxial cable at 1 GHz? (b) What determines the maximum power that we may transmit into a cable? (c) Assuming a minimum
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hw1 - University of California, Berkeley EECS 142 Fall 2011...

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