The Telephone

Analog vs Digital View the video first: Digital Digital

Analog vs Digital Analog Wave - analog wave representing the vibrations created by your voice.

Analog vs Digital However, most things we use in this day and age are passed along via digital information. Examples : CD’s, MP3 players, Cell Phones, TV’s, and pretty much all electronic devices from our current era. Electronics have devices called analog-to- digital converter (ADC) and digital-to-analog converter (DAC).

Analog vs Digital Example: – a phone takes our voice, which is in analog form, and convert it to digital information to pass it along the wires/stellates/towers to the receiver of your phone call which then converts the digital information into an analog form so they can make sense of your words. All our electronic devices mentioned in the previous slide do this.

Analog vs Digital An ADC converts the analog wave into a stream of numbers and records the numbers instead of the wave. The following graphs show how analog is transferred to digital information.

Analog vs Digital Analog Wave needs to be turned into a digital wave.

Analog vs Digital The green line represents a sample of digital information that is created from the analog wave. This is example creates 1,000 samples per second Problem here is the green lines do not accurately collect the precise sound wave.

Analog vs Digital This converter is at a rate of 4,000 samples per second. Notice that this one is a little more precise.

Analog vs Digital This converter is information at 44,100 samples per second. This one produces digital information that is almost precise to the analog wave.

Analog vs Digital Information at a radio station, or a cellphone tower, or a radio tower, or telephone fiber optics release an analog or digital information. Our devices have a receiver that reads these waves and converts it into an analog or digital information as needed via an ADC or DAC. So how is it these waves do not get mixed up in the air?

Analog vs Digital Band/ UseWavelengthFrequency LW (Long wave)5km–1km60kHz–300kHz AM/MW (Amplitude modulation / medium wave)600m–176m500kHz–1.7MHz SW (Short wave)188m–10m1.6MHz–30MHz VHF/FM (Very high frequency / frequency modulation) 10m–6m100MHz–500MHz FM (frequency modulation)3.4m–2.8m88MHz–125Mhz Aircraft2.7m–2.2m108–135MHz Cellphones80cm–15cm380–2000MHz Radar100cm–3mm0.3–100GHz

The Telephone

Components of the Telephone A switch - to connect and disconnect the phone from the network. This switch is generally called the hook switch. It connects when you lift the handset. A speaker - This is generally a little 50-cent, 8- ohm speaker A microphone - electronic microphone, amplifier and circuit. A duplex coil - blocks the sound of your own voice from reaching your ear when you speak into the microphone.

A Visual of a real Telephone

How a phone signal is transferred ne3.htm ne3.htm

Telephone Tones A modern phone system has an electronic switch. When you pick up the phone, the switch senses the completion of your loop and it plays a dial tone sound so you know that the switch and your phone are working. A dial tone sound is simply a combination of 350-hertz tone and a 440-hertz tone.

Dial Tones The different dialing sounds are made of pairs of tones Sound of a typical tone 1 = 697 Hz + 1,209 Hz 2 = 697 Hz + 1,336 Hz 3 = 697 Hz + 1,477 Hz 4 = 770 Hz + 1,209 Hz 5 = 770 Hz + 1,336 Hz 6 = 770 Hz + 1,477 Hz 7 = 852 Hz + 1,209 Hz 8 = 852 Hz + 1,336 Hz 9 = 852 Hz + 1,477 Hz * = 941 Hz + 1,209 Hz 0 = 941 Hz + 1,336 Hz # = 941 Hz + 1,477 Hz

Busy Tone A busy signal that is made up of a 480-hertz and a 620-hertz tone, with a cycle of one-half second on and one-half second off, like this:

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