1. Audio and Video Communication

2. Transmission of Audio Without wires - This is radio.
Using wires - this is what we typically think of as basic telephone technology.
Cell Phones – Microwaves (E&M waves) and Fiberoptic cables
Internet – Satellites, phone lines, Fiberoptics (both wireless and wired)

3. Cell Phone Frequency Range: 850 and 1900 MHz

4. Cell phones and Microwave Ovens are close together on the Frequency Spectrum…
Microwave Ovens use 2.45 GHz (GHz = 109 cycles per second)
GSM Cell Phones use 850MHz and 1.9GHz
Why don’t cell phones “cook” you?

5. How a Microwave Works
Microwaves are absorbed by water, fats, and sugars (the stuff in food)
Water is a dipole molecule with a positive and negative side
Water molecules constantly flip over, trying to align themselves with the changing electric field of the microwave
As the water molecules flip over they rub against each other making heat

6. Transformer steps up the voltage to 2000 volts
Magnetron produces the microwave
Waveguide leads wave into oven cavity

7. Difference between Cell Phone and Microwave Oven
Power
Cell Phone Watts
Microwave 1000 Watts
Amplitude
Modulation
Cell phone is carrying info
Microwave is not

8. More Information can be transmitted if information is Digitized

9. Voice and Music are analog data Dots-Dashes, 1’s and 0’s, on-off are examples of digital data
Digital information is coding a signal using a binary format, e.g. 0’s and 1’s, dots and dashes, on and off, Morse Codes, etc.
Analog is the process of converting a signal into a wide range of continuous values.

10. Photographic picture is an analog image.
Digital picture is made up of many pixels, each pixel is one color.

11. Record Vinyl is analog data
Record Vinyl is analog data. The grooves are carved by a needle that was moved by a vibrating needle attached to a diaphragm. The groves are analog as they are a continuous representation of the audio information.
birminghamstories.co.uk

12. Record Needle - Stylus
Placed in the grooves of the recorded disc and transfers its vibrations to a magnet that induces a current in a nearby coil, creating an electrical signal that corresponds to the audio.
As the stylus rides along the walls of the moving groove, it vibrates back and forth with each ripple in a wall. Two transducers attached to this stylus sense its motions and produce electric currents that are related to those motions.
Transducer:
Converts input energy of one form into output energy of another form.
Louis A. Bloomfield

13. Electromagnets used in Tape Players too
The electromagnet consists of an iron core wrapped with wire, as shown in the figure. During recording, the audio signal is sent through the coil of wire to create a magnetic field in the core.
This flux is what magnetizes the oxide on the tape. During playback, the motion of the tape pulls a varying magnetic field across the gap. This creates a varying magnetic field in the core and induces signal in the coil that corresponds to the audio.
A – Tape
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Tapes can store analog data (a continuous signal) or can be DAT (Digital Audio Tapes)

14. Transmission of Audio This is Amplitude Modulation (AM)
Amplitude is volume and frequency is the pitch.
Audible range:
20 Hz - 20 kHz
Turned into a Electromagnetic Wave

15. This is Frequency Modulation (FM).
This requires greater bandwidth but it is easier to cancel out noise.
Turned into a Electromagnetic Wave

16. Transmission of Analog Data (Listening to the Radio or talking on the phone ) was preferred over Morse Codes (dots and dashes) because:
Transmitting dots and dashes (digital data) required a human computer to decode the message.
Transmission speed was slow

17. Voice data can be automatically sent digitally by digitizing the audio and then reassembling the audio later.
Periodically take a sample, at a rate of at least ½ the frequency. The more samples the more information is captured. /

18. Digitized Sounds

19. CD Rom- Digital data storage
Data is represented as pits and bumps
Track is a outward moving spiral

20. CD Bumps are the digital data
Data Track is typically 3 ½ miles long.

21. Reading the bumps with a laser and optical sensor

22. Click for animation

23. The tracking drive keeps the laser under the track.
The disk motor spins between rpm as the laser moves outward with the track.
Animation at:

24. How data is arranged on CDs
Data is interleaved so scratches on the CD won’t be a complete loss of data
Data is read one revolution at a time, and software orders the interleaved data in the correct sequence.
Extra data is present for error-checking
Meta-Data is present to identify songs

25. Video Communication Producing Video Images Capturing Video data
Transmission via cable
Transmission wireless
Storing Video data on VHS Tape
Displays
CRT
LCD
Plasma
Digital TV and DVDs

26. Brain assembles pixels into images
Higher resolution means more dots/pixels for a given area
Higher Res. Means sharper image
Brain fuses pixels
How Stuff Works

27. Brain assembles still images into a life-like moving image
19th century novelty items
Old movies – frames/sec
Theaters – 24 frames/sec
TV – 30 frames/sec

28. Praxinoscope

29. TV ‘paints’ image with three electron beams
Hot Cathode emits electrons.

30. Shadow Mask holes are arranged so that each electron beam corresponds to one color and can only excite one phosphor dot

31. Steering coils around CRT position the electron beams using magnetic fields
CRT - Cathode Ray Tube

32. Electron Beams ‘paint’ the screen using a raster scan pattern
525 Lines are ‘painted’ every 1/30 second.
Each line has 680 pixels.

33. Lines are interleaved Every other line is painted to reduce flicker
Odd lines are ‘painted’ in 1/60 of a sec. followed by even lines painted next.

34. Inside of the screen is coated with stripes made of three phosphors: They each glow red, green, or blue.
Shadow Mask ensures that each beam strikes only the phosphor it was intended for.

35. Colors are fused by the Brain
RGB can be mixed to create any color of varying intensity.

36. TV broadcast uses Radio Signals
Each station allocated 6 MHz
54 to 88 MHz for VHF channels 2 to 6
174 to 216 MHz for channels 7 through 13
470 to 890 MHz for UHF channels 14 through 83

37. TV uses AM for video and FM for audio

38. Luminance (intensity), Chromaticity (color), and sound

39. Luminance for one line

40. Chrominance Signal
Phase shift after sine wave determines color for one pixel.

41. Recording onto tape
Video Head Drum is tilted with respect to the tape. This creates diagonal video tracks.
The drum rotates quickly, making long video tracks.
There are two record/read heads attached to the rotating drum.
One screen picture is two diagonal tracks, or one rotation of the drum.
Yellow tracks are audio and control tracks

42. Magnetic Data on Tape
Control Track indicates if this is a SP, LP, or EP and thus determines how fast to pull the tape. It also ensures the heads are lined up correctly during playback.
Audio track is recorded and read similar to tape deck.

43. TV goes Digital in Feb. 2009
19.39-megabit-per-second (Mbps) stream of digital data
Multiple formats can be transmitted
Standard Definition
High Definition (HDTV)

44. Digital Modulation Techniques
Phase Shift Keying (Bluetooth, Wireless LANs)
Frequency Shift Keying (GSM Phones)
Amplitude Shift Keying (Sending Morse Codes using Telegraph, optical fibers send pulses of light representing 1’s and 0’s)
Some Combination of the above

45. Monitors Cathode Ray Tube (CRT) Flat Panel (Liquid Crystal Display)
In most TVs
Bulky, heavy, higher power
Good color and display
Image needs to be refreshed
Warm-up time requirement
Flat Panel (Liquid Crystal Display)
More expensive
Images may vary based on viewing angle
Low Power

46. Polarized vs. non-Polarized Light
Light with the Electric Field in one orientation is polarized light.

47. Liquid Crystal Displays
Glass plates are electrodes
Applying a voltage across the plates aligns the liquid crystals parallel to the voltage
Small one-directional scratches on the glass plates cause the crystals to twist when there is no voltage

48. Polarizing Filters
A thin film on a surface absorbs light with the horizontal orientation.
Only light with a non-horizontal orientation passes through.

49. Liquid Crystal Displays
LCDs block light creating darkness
Vertical Polarizing Filter
7-segment display with metal oxide that is both transparent & conductive. Backside has verticals ridges.
Liquid crystals
Layer with horizontal ridges
Horizontal Polarizing Filter
Reflective layer to reflect light back to your eye
wikipedia

50. LCD with applied voltage – light is blocked or absorbed by filters creating darkness.
LCD without voltage – light is passed through or reflected

51. Color is achieved with three sub-pixels: Red, Green, Blue
Voltage for each color determines intensity of the sub-pixel.
Color filters filter out all light but the one color for the sub-pixel.

52. Sources http://www.howstuffworks.com/tv.htm