STEM Blog
The Sonic Boom
In 1986, a Royal Australian Air Force pilot was fined $100 for disobeying orders and flying faster than the speed of sound over the city of Adelaide, Australia. His plane’s sonic boom caused $512,000 worth of damage to buildings, including $256,000 worth of damage to a single greenhouse by shattering its walls. What is a…
The Doppler Effect
If you’ve ever been standing on the curb as a car or truck races past with its horn blaring, you’ve noticed that the tone of the horn appears to change as the vehicle goes by. The driver inside, leaning on the horn, doesn’t notice any change in frequency at all as she whizzes past at…
Radar Basics
With everything we’re already learned about the electromagnetic spectrum, this is an opportune time to talk about radar, something we rely on in our everyday lives. When you access a weather app like Storm Radar on your cell phone, you can actually view a picture of your local area, informed by radar. Weather forecasters use…
Understanding Cell Phone Technology: Antennas
I thought I had finished talking about cell phones. Then a colleague of mine asked when I was going to talk about cell phone antennas. So we’ll talk a little about cell phone antennas today and move on to a new topic next week. Every cell phone has multiple antennas because every cell phone has…
Understanding Cell Phone Technology: Frequency Bands and Modulation
Several weeks ago, we talked about the different bands of the electromagnetic spectrum. Each band corresponds to a range of frequencies, measured in cycles/second or Hertz (Hz). One of those bands is the Radio Frequency (RF) band. In the United States, the Federal Communications Commission (FCC) is responsible for regulating the use of this radio…
Understanding Cell Phone Technology: Convolutional Codes
Today we’re going to talk about convolutional codes. Like block codes, convolutional codes are used in our cell phones to detect and correct errors introduced by noise on the transmission channel. Unlike block codes, these error correcting codes have memory. An (n, k, m) convolutional code depends on m previous message blocks, taking in a…
Understanding Cell Phone Technology: Block Codes for Error Control
The design of block codes relies on abstract algebra. Abstract algebra is all about sets of elements with special attributes. For example, a group is a set of elements with a defined operation that is closed, associative, and contains an identity and inverse for every element. By closed, we mean that the element resulting from applying an…
Understanding Cell Phone Technology: Error Control Strategies
Happy New Year’s! We’re going to digress today and talk about different strategies used to control errors on communications channels. We have to use Forward Error Correction (FEC), like block codes and convolutional codes, on one-way communications channels. These are error controlling codes that detect and correct (at least some of the) errors at the…
Understanding Cell Phone Technology: Error Correcting Codes
Error correcting codes came along after Claude Shannon proved that the use of suitable codes permitted reliable information transmission across a noisy channel at rates approaching the channel capacity. By “codes”, Shannon actually meant codes for data compression and codes for error correction. We’re already spent several weeks talking about compression algorithms, available in lossless…
Understanding Cell Phone Technology: Lossy Data Compression
Last week we began looking at data compression codes. We talked about three lossless compression schemes: Morse, Huffman, and Lempel Ziv (LZ). This week we’re going to turn our attention to methods for lossy compression. Lossy compression? Why would anyone want lossy compression, that is, a compression code that actually throws away some of the…