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`Electrical Engineering Tutorials
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`We will introduce some of electrical and communication tutorials that will help you overcome misunderstanding of electrical and communication
`concepts.
`
`Blog Archive
`▼ 2010 (2)
`▼ December (2)
`▼ Dec 11 (1)
`How Cordless
`Telephones Work
`▶ Dec 10 (1)
`
`Saturday, December 11, 2010
`How Cordless Telephones Work
`1. Introduction to How Cordless Telephones
`Work
`
`Cordless telephones are one of those minor miracles of modern life -- with a
`cordless phone, you can talk on the phone while moving freely about your house
`or in your yard. Long before cell phones became so cheap that anyone could
`afford one, cordless phones gave everyone the freedom to walk and talk within
`the privacy of their own homes.
`Cordless phones have many of the same features as standard telephones, and
`there are many models available. In this article, we will examine how these
`cordless telephones work and see why there are so many different types on the
`market today.
` 2. The Basics
`A cordless telephone is basically a combination telephone and radio transmitter/receiver (see How
`Telephones Work and How Radio Works for details on these two technologies). A cordless phone has
`two major parts: base and handset.
`The base is attached to the phone jack through a standard phone wire connection, and as
`far as the phone system is concerned it looks just like a normal phone. The base receives
`the incoming call (as an electrical signal) through the phone line, converts it to an FM radio
`signal and then broadcasts that signal.
`The handset receives the radio signal from the base, converts it to an electrical signal and
`sends that signal to the speaker, where it is converted into the sound you hear. When you
`talk, the handset broadcasts your voice through a second FM radio signal back to the
`base. The base receives your voice signal, converts it to an electrical signal and sends
`that signal through the phone line to the other party.
`The base and handset operate on a frequency pair that allows you to talk and listen at the same time,
`called duplex frequency.
`
`http://aboashoor.blogspot.com/2010/12/how-cordless-telephones-work.html
`
`Page 1 of 12
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`Carucel Investments—Exhibit 2103
`IPR2019-01079: Unified Patents, Inc. v. Carucel Investments L.P.
`Page 1
`
`
`
`Electrical Engineering Tutorials: How Cordless Telephones Work
`
`1/23/20, 1(55 PM
`
`Diagram showing how the base unit and handset of the cordless phone talk to each other:
`Each color represents a different frequency.
`3. A Brief History
`Cordless phones first appeared around 1980. The earliest cordless phones operated at a frequency
`of 27 MHz. They had the following problems:
`limited range
`poor sound quality - noisy and ridden with static because walls and appliances interfered
`with the signals
`poor security - people could easily intercept signals from another cordless phone because
`of the limited number of channels
`In 1986, the Federal Communications Commission (FCC) granted the frequency range of 47-49 MHz
`for cordless phones, which improved their interference problem and reduced the power needed to run
`them. However, the phones still had a limited range and poor sound quality.
`Because the 43-50 MHz cordless phone frequency was becoming increasingly crowded, the FCC
`granted the frequency range of 900 MHz in 1990. This higher frequency allowed cordless phones to
`be clearer, broadcast a longer distance and choose from more channels. However, cordless phones
`were still quite expensive, about $400.
`In 1994, digital cordless phones in the 900 MHz frequency range were introduced. Digital signals
`allowed the phones to be more secure and decreased eavesdropping -- it was pretty easy to
`eavesdrop on analog cordless phone conversations. In 1995, digital spread spectrum (DSS) was
`introduced for cordless phones. This technology enabled the digital information to spread in pieces
`over several frequencies between the receiver and the base, thereby making it almost impossible to
`eavesdrop on the cordless conversations.
`In 1998, the FCC opened up the 2.4 GHz range for cordless phone use. This frequency has
`increased the distance over which a cordless phone can operate, and brought it out of the frequency
`range of most radio scanners, thereby further increasing security.
`4. Anatomy of a Cordless Telephone
`To illustrate the parts of a cordless telephone, we will show you the inside of this one from General
`Electric (GE). It was made in 1993 and operated in the 43-50 MHz range.
`
`http://aboashoor.blogspot.com/2010/12/how-cordless-telephones-work.html
`
`Page 2 of 12
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`Carucel Investments—Exhibit 2103
`IPR2019-01079: Unified Patents, Inc. v. Carucel Investments L.P.
`Page 2
`
`
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`Electrical Engineering Tutorials: How Cordless Telephones Work
`
`1/23/20, 1(55 PM
`
`GE cordless phone, including handset and base unit
`As mentioned above, all cordless phones have a base and a handset. Let's look at these parts
`individually.
`Base
`The base unit of the cordless phone is plugged into the telephone jack on your wall.
`
`Base unit components
`If you open up the base and expose the circuit board, you see several components that carry out the
`functions of the base:
`phone line interface - receives and sends telephone signals through the phone line
`radio
`
`amplifies signals to and from phone-line interface, user controls and speaker
`phone (if present)
`broadcasts and receives radio signals to and from the handset
`
`power - supplies low voltage power to the circuits and recharges the battery of the
`
`http://aboashoor.blogspot.com/2010/12/how-cordless-telephones-work.html
`
`Page 3 of 12
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`Carucel Investments—Exhibit 2103
`IPR2019-01079: Unified Patents, Inc. v. Carucel Investments L.P.
`Page 3
`
`
`
`Electrical Engineering Tutorials: How Cordless Telephones Work
`
`1/23/20, 1(55 PM
`
`handset
`
`Circuit board in the base of the GE cordless phone
`
`Phone Line Interface
`Phone line interface components do two things. First, they send the ringer signal to the bell (if it's on
`the base) or to the radio components for broadcast to the handset. This lets you know that you have
`an incoming call. Second, they receive and send small changes in the phone line's electrical current
`to and from the radio components of the base. When you talk, you cause small changes in the
`electrical current of the phone line, and these changes get sent to your caller. The same happens
`when the caller talks to you.
`Radio Components
`The radio components receive the electrical signals from the phone line interface and user controls
`(keypads, buttons). The radio components convert the signals to radio waves and broadcast them via
`the antenna. Radio components use quartz crystals to set the radio frequencies for sending and
`receiving. There are two quartz crystals, one for sending signals and one for receiving signals.
`Remember that the base and handset operate on a frequency pair that allows you to talk and listen at
`the same time (duplex). The radio components include an audio amplifier that increases the strength
`of the incoming electrical signals.
`Power Components
`A DC power cube transformer supplies the low voltage required by the electrical components on the
`circuit board. The power components on the circuit board work with the power cube to supply
`electrical current to re-charge the battery of the handset.
`In addition to the above components, some bases also have audio amplifiers to drive speakers for
`speaker phone features, keypads for dialing, liquid crystal displays (LCDs) for caller ID, light-emitting
`diodes (LEDs) for power/charging indicators, and solid state memory for answering machine or call-
`back features.
`Handset
`You can carry the handset with you throughout the house or outside within the range of
`the base transmitter. The handset has all of the equipment of a standard telephone
`(speaker, microphone, dialing keypad), plus the equipment of an FM radio
`transmitter/receiver.
`
`http://aboashoor.blogspot.com/2010/12/how-cordless-telephones-work.html
`
`Page 4 of 12
`
`Carucel Investments—Exhibit 2103
`IPR2019-01079: Unified Patents, Inc. v. Carucel Investments L.P.
`Page 4
`
`
`
`Electrical Engineering Tutorials: How Cordless Telephones Work
`
`1/23/20, 1(55 PM
`
`Block diagram of handset components
`When you open up the handset, you see these components:
`speaker - converts electrical signals into the sound that you hear
`microphone - picks up your voice and changes it to electrical signals
`keypad - input for dialing
`buzzer or ringer - lets you know that you have an incoming call
`radio components
`amplify electrical signals to and from microphone and speakers
`send and receive FM radio frequencies
`
`LCD or LED displays - indicator lights
`re-chargeable battery - supplies electrical power to handset
`
`Parts of the GE cordless phone's handset, showing the fronts
`of the circuit boards
`
`http://aboashoor.blogspot.com/2010/12/how-cordless-telephones-work.html
`
`Page 5 of 12
`
`Carucel Investments—Exhibit 2103
`IPR2019-01079: Unified Patents, Inc. v. Carucel Investments L.P.
`Page 5
`
`
`
`Electrical Engineering Tutorials: How Cordless Telephones Work
`
`1/23/20, 1(55 PM
`
`Parts of the GE cordless phone's handset, showing the backs of the
`circuit boards, the speaker, microphone, ringer and battery
`
`Speaker
`The speaker receives the electrical signals from the audio amplifier in the radio components and
`converts them into sound. When you remove the cover from the speaker, you see a large round
`permanent magnet with a hole in the middle and a deep groove surrounding the hole. Within this
`deep groove is a coil of fine copper wire that is attached to a thin plastic membrane. The plastic
`membrane covers the magnet and coil.
`
`Close-up view of the speaker in the GE cordless telephone
`handset
`
`http://aboashoor.blogspot.com/2010/12/how-cordless-telephones-work.html
`
`Page 6 of 12
`
`Carucel Investments—Exhibit 2103
`IPR2019-01079: Unified Patents, Inc. v. Carucel Investments L.P.
`Page 6
`
`
`
`Electrical Engineering Tutorials: How Cordless Telephones Work
`
`1/23/20, 1(55 PM
`
`Close-up of the speaker with the top removed
`
`Close-up of the speaker with the plastic membrane and attached coil lifted out.
`The large metal disc is the magnet.
`
`Close-up of the speaker's plastic membrane with attached wire coil
`To hear sounds, the following events happen:
`1. Electrical signals come from the radio components.
`2. The electrical signals travel in the coil of copper wire.
`3. The electrical signals induce magnetic currents in the coil of wire, thereby making it an
`electromagnet.
`4. The electromagnetic coil moves in and out of the groove within the permanent magnet.
`5. The coil moves the attached plastic membrane in and out at the same frequencies as the
`changes in electric currents.
`6. The movements of the membrane move air at the same frequencies, thereby creating sound
`
`http://aboashoor.blogspot.com/2010/12/how-cordless-telephones-work.html
`
`Page 7 of 12
`
`Carucel Investments—Exhibit 2103
`IPR2019-01079: Unified Patents, Inc. v. Carucel Investments L.P.
`Page 7
`
`
`
`Electrical Engineering Tutorials: How Cordless Telephones Work
`
`1/23/20, 1(55 PM
`
`waves that you can hear.
`Microphone
`The microphone changes the sound waves from your voice into electrical signals that are sent to the
`audio amplifier of the radio components. A microphone is essentially a speaker that works in reverse.
`When sound waves from your voice move the membrane, they make tiny electric currents either by
`moving a coil of wire within a magnet or by compressing the membrane against carbon dust (see How
`do microphones work? for details).
`
`Close-up of handset's keypad circuit board with attached
`microphone and buzzer
`
`Keypad
`The keypad allows you to dial a number. It transfers the pressure from your fingertip on the
`appropriate key into an electrical signal that it sends to the radio components. Below the rubber
`keypad is a circuit board with black conductive material under each button (shown above). The
`keypad works like a remote control. When you press a button, it makes a contact with the black
`material and changes its electrical conductance. The conductance sends an electrical signal to the
`radio components indicating that you have selected that number.
`Buzzer or Ringer
`When the radio components of the handset receive the ringer signal from the base, they send
`electrical signals to the buzzer. The buzzer changes those electrical signals into sound much like the
`speaker does. You hear the buzzer sound and know that someone is calling you. In some phones, the
`speaker is used to make the ringer sound and there is no need for a separate ringer.
`Duplex Example
`Base:
`44.32 MHz transmitter
`49.28 MHz receiver
`Handset:
`49.28 MHz transmitter
`44.32 MHz receiver
`Radio Components
`The radio components of the handset are like those of the base -- they convert electrical signals from
`the microphone into FM radio signals and broadcast them at the same frequency as the receiving
`crystal of the base unit. The radio components also receive radio signals at the same frequency as
`the broadcasting crystal from the base, convert them to electrical signals and send them to the
`speaker and/or buzzer (ringer).
`Remember that the base and handset operate on a duplex frequency pair that allows you to talk and
`listen at the same time.
`LCD or LED Displays
`Most handsets have one or more light-emitting diodes (LED) that indicate various things, such as
`when the phone has an open line or when the battery is low.
`
`http://aboashoor.blogspot.com/2010/12/how-cordless-telephones-work.html
`
`Page 8 of 12
`
`Carucel Investments—Exhibit 2103
`IPR2019-01079: Unified Patents, Inc. v. Carucel Investments L.P.
`Page 8
`
`
`
`Electrical Engineering Tutorials: How Cordless Telephones Work
`
`1/23/20, 1(55 PM
`
`LED indicator light on the handset of the GE cordless phone
`Some handsets have an LCD that can display numbers for caller ID features, similar to a cell phone.
`The LCD may be reflective or backlit so that you can see it when the room light is low.
`Battery
`The handset's battery supplies the power for all of the electrical components in the handset. All
`cordless phone handsets have a rechargeable battery (nickel-cadmium, nickel-metal hydride or
`lithium). When the battery runs low, an indicator light on the handset usually lights up or flashes. In
`some phones, a "beeping" sound may also indicate a low battery. You then recharge the battery on
`the base of the cordless phone.
`The GE cordless phone that we dissected was from 1993. Modern cordless phones have the same
`functions and much of the same hardware. However, many of the electronic circuits that were once
`achieved with transistors, resistors and capacitors have been replaced with integrated circuits. This
`advancement allows the handset to be either smaller with the same functions or the same size with
`more functions.
`In summary, a cordless phone is basically a combination of a telephone and an FM radio
`transmitter/receiver. Because it is a radio transmitter, it broadcasts signals over the open airways
`rather than specifically between the base and handset.
`
`Many cordless phone conversations can be easily picked up by
`radio scanners.
`Because of this open broadcast, It is possible for other people to listen to your phone conversation by
`using a radio scanner. So an important issue and feature to look for in a cordless phone is security --
`
`http://aboashoor.blogspot.com/2010/12/how-cordless-telephones-work.html
`
`Page 9 of 12
`
`Carucel Investments—Exhibit 2103
`IPR2019-01079: Unified Patents, Inc. v. Carucel Investments L.P.
`Page 9
`
`
`
`Electrical Engineering Tutorials: How Cordless Telephones Work
`
`1/23/20, 1(55 PM
`
`DSS offers the best protection against eavesdropping.
`5. Features
`Cordless phones have many of the same features as standard telephones, and there are many
`models, offering lots of different features.
`Major Features
`Remember that a cordless telephone is a combination of a telephone and a radio
`transmitter/receiver. Because it is a radio transmitter/receiver, you have the following issues that
`you do not have on a standard cord phone:
`range
`sound quality
`security
`The range is the distance that the handset can be from the base. The sound quality can be affected
`by the distance, the way the information in the radio signal is transmitted, and interfering structures
`such as walls and appliances. Security is an issue because the radio signals from both handset and
`receiver go over the open airways, where they can be picked up by other devices (other cordless
`phones, baby monitors, radio scanners).
`The above issues relate to the following features of your cordless phone:
`radio frequency
`analog vs. digital technology
`number of channels
`Frequency
`Because your cordless phone is a radio transmitter/receiver, it operates on various radio frequencies,
`which are set by the Federal Communications Commission (FCC) as with any other radio. Cordless
`phones operate over three major frequency bands (base and receiver use two closely related but
`separate frequencies within the band so that you can talk and listen at the same time):
`43-50 MHz
`900 MHz
`2.4 GHz
`5.8 GHz
`The 43-50 MHz band was common to early cordless telephones and is still available in low-cost
`models. Because of the low frequency, these phones have short ranges (about 1,000 ft / 330 m) and
`poorer sound quality (due to interference from structures and appliances). The 43-50 MHz phone
`signals can also be picked up easily on radio scanners and nearby baby monitors.
`The 900 MHz band (actually 900-928 MHz) is the most common frequency for cordless phones today.
`The higher frequency gives it a greater range (5,000 to 7,000 ft / 1,500 to 2,100 m) and better sound
`quality. However, 900 MHz signals can be picked up easily by most commercially available radio
`scanners.
`In 1998, the FCC opened up the 2.4 GHz range for cordless phone use. A 2.4 GHz or 5.8 GHz
`cordless phone can operate over a greater distance and is above the frequencies that can be picked
`up by most commercially available radio scanners; therefore, it is more secure than lower frequency
`models.
`Analog vs. Digital
`Analog technology is common in cordless telephones, especially in inexpensive models. Analog
`signals tend to be more noisy, or prone to interference with respect to sound quality. In addition,
`analog signals are easily picked up and interpreted by radio scanners.
`In contrast, digital technology, like that found in a CD, allows the phone signals to sound clearer.
`Furthermore, digital signals are more secure. In 1995, digital spread spectrum (DSS) was introduced
`for cordless phones. DSS spread the digital information in pieces over several frequencies between
`the receiver and the base, thereby making it almost impossible to eavesdrop on cordless phone
`conversations.
`Channels
`Each frequency band (43-50 MHz, 900 MHz, 2.4 GHz or 5.8 GHz) can be subdivided into different
`increments or channels. For example, on some models, when you're talking on your 900 MHz phone,
`the base searches for a pair of frequencies (channels) within that range, that is not already in use, in
`order to talk to the handset. So, if the base is capable of searching more increments, it can more
`easily find a frequency pair that is clear from interference, providing better sound quality. The number
`
`http://aboashoor.blogspot.com/2010/12/how-cordless-telephones-work.html
`
`Page 10 of 12
`
`Carucel Investments—Exhibit 2103
`IPR2019-01079: Unified Patents, Inc. v. Carucel Investments L.P.
`Page 10
`
`
`
`Electrical Engineering Tutorials: How Cordless Telephones Work
`
`1/23/20, 1(55 PM
`
`of cordless phone channels can vary as follows:
`10 to 25 channels - 43-50 MHz phones, some inexpensive 900 MHz phones
`20 to 60 channels - most 900 MHz phones
`50 to 100 channels - high-end 900 MHz and 2.4/5.8 GHz phones
`6. When You Shop
`Popular Cordless Telephones
`Here are some of the best-selling cordless telephone models listed for comparison.
`
`Panasonic KX TG2750S
`2.4 GHz with Call-waiting Caller
`ID
`
`AT&T 5840
`5.8GHz with DSS
`
`Panasonic KX-TG5050
`5.8 GHz with Caller ID
`
`Panasonic KX TG2730
`Multi-Talk 2.4GHz
`
`Look Out!
`When buying a cordless telephone, there are several things you should keep in mind to avoid buying
`one that won't meet all your needs. Here are some of the most important things to think about:
`Security, security, security!
`Because your cordless phone is a radio transmitter, it broadcasts signals over the open airways rather
`than specifically between the base and handset. Therefore, it is possible for other people to listen to
`your phone conversation by using a radio scanner. Digital phones are better than analog phones in
`this area, but DSS offers the best protection against eavesdropping. Low-end 43-50 MHz and 900
`MHz analog phones are not secure. In fact, most baby monitors can pick up phone conversations
`from 43-50 MHz cordless phones. 2.4 GHz analog phones are rare (most 2.4 GHz phones are
`digital), but offer some degree of protection because most commercially available radio scanners do
`not extend into this radio frequency.
`If your cordless phone does not have DSS, then your conversation is about as private as the writing
`on the back of a postcard. Use care when divulging private information over a cordless phone.
`Think about the type of battery in your cordless phone!
`All cordless phone handsets have a rechargeable battery (nickel-cadmium, nickel-metal hydride,
`lithium). Nickel-cadmium batteries are subject to a memory effect, so it is best to let them drain
`entirely before recharging them on the base. Nickel-metal hydride and lithium batteries have no
`memory effect.
`
`Posted by AbOaShOoR Software and Learning WebSite at 2:27 PM
`Labels: Cordless
`
`http://aboashoor.blogspot.com/2010/12/how-cordless-telephones-work.html
`
`Page 11 of 12
`
`Carucel Investments—Exhibit 2103
`IPR2019-01079: Unified Patents, Inc. v. Carucel Investments L.P.
`Page 11
`
`
`
`Electrical Engineering Tutorials: How Cordless Telephones Work
`
`1/23/20, 1(55 PM
`
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`http://aboashoor.blogspot.com/2010/12/how-cordless-telephones-work.html
`
`Page 12 of 12
`
`Carucel Investments—Exhibit 2103
`IPR2019-01079: Unified Patents, Inc. v. Carucel Investments L.P.
`Page 12
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`