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 cell phone freedom within the
privacy of their own homes. With some features, you can now
have three-way conversations, page someone within your house
or work with your hands while you talk on the phone.
Cordless phones have many of the same features as standard
telephones
and there are many models available. In this edition of How Stuff
Works, we will examine how these cordless telephones
work and why there are so many different types on the market
today!
To access all of the different parts of this article,
choose from the map below:
You may want to start with "How They Work" to learn the
basics about cordless phones. If you are thinking about buying
one, be sure to look at the Features
section to learn about all of the features you should keep in
mind to buy the right cordless phone for you.
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.
 Diagram showing how the base unit and handset
of the cordless phone talk to each other. Each color
represents a different
frequency.
|
To learn more about how cordless phones work click
here, or choose from the map below:
A Brief History of Cordless
Telephones
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.
To learn more about how cordless phones work click
here, or choose from the map below:
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.
 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.
To examine the parts of a cordless phone click
here, or choose from the map below:
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 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 (LCD) for caller ID, light-emitting
diodes (LED) for power/charging indicators, and solid
state memory for answering machine or call-back features.
To learn more about how cordless phones work click
here, or choose from the map below:
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.
 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
|
 Parts of the GE cordless phone's handset,
showing the backs of the circuit boards, the speaker,
microphone, ringer and
battery
|
To learn more about handsets click
here, or choose from the map below:
Handset Components
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
|
 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:
- Electrical signals come from the radio components.
- The electrical signals travel in the coil of copper
wire.
- The electrical signals induce magnetic currents in the
coil of wire, thereby making it an electromagnet.
- The electromagnetic coil moves in and out of the groove
within the permanent magnet.
- The coil moves the attached plastic membrane in and out
at the same frequencies as the changes in electric currents.
- The movements of the membrane move air at the same
frequencies, thereby creating sound
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 question
309 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.
Radio Components
Duplex ExampleBase:
- 44.32 MHz transmitter
- 49.28 MHz receiver
Handset:
- 49.28 MHz transmitter
- 44.32 MHz receiver
|
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.
 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 -- DSS
offers the best protection against eavesdropping.
To go on to the "Features" section click
here, or choose from the map below:
Features
Cordless
phones have many of the same features as standard telephones,
and there are many models, offering lots of different
features. In this section of How
Cordless Phones Work, we will examine the various features
on these portable telephones.
When you think about cordless phone features, consider the
following categories:
- major features of the phone - range, sound
quality, security
- convenience features of the phone - ease of use
- options in combination with the phone service -
making the most of your phone
To learn about features click
here, or choose from the map below:
Major Features
Remember that a cordless
telephone is a combination of a telephone and a
radio transmitter/receiver (see How
a Cordless Telephone Works for details). 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:
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
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 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. A
2.4 GHz cordless phone will be more expensive than a lower
frequency phone.
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 or 2.4 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 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 GHz
phones
To learn about convenience features click
here, or choose from the map below:
Convenience Features
Convenience features
make the cordless phone easier to use or more versatile; some
of these features are identical to those in standard cord
phones. Convenience features include the following:
- speaker phones
- pager/handset locator
- indicators
- redial
- one-touch dialing/programmable
- volume control
- mute/hold
- ringer in base
- keypad on base
- battery
- extra battery charger
- hands-free headset
- wall mount
Speaker Phones
Speaker
phones can be on the base and/or handset. Speaker phones have
a microphone that can pick up the sounds around them and a
speaker to broadcast incoming sounds. With a speaker phone,
more than one person can talk and listen to the call at the
same time. You can use a speaker phone for conferences or
family conversations.
Pager/Handset
Locator
With this feature, a button can be pressed
on either the handset or the base to find whichever part
you're missing. The button sends a radio signal to the other
unit, and when the other unit receives the radio signal it
sets off a beeper. This feature is most helpful in locating
the handset. For example, my 19 month old son frequently runs
off with our cordless handset and hides it somewhere. This
feature makes it easy to find the handset. In addition, this
feature can be used to page someone, or as an intercom. When I
am upstairs and my wife is downstairs, we can use this feature
to ask each other questions over the phone without having to
yell up or down the staircase, because my base unit has a
speaker phone.
Indicators
Indicators on
the handset can be combinations of beeping sounds, LCD messages and
flashing LED
lights that tell you when your battery is low and needs to be
recharged or when you are getting out of range of the phone's
base unit. On the base unit, the indicators can tell you when
the handset is done charging or off the hook.
Redial
With this feature,
the handset or base unit has a memory
chip that can store the last number called by the phone.
To redial the number, you just touch the button on the handset
and/or base and it dials that number through the phone line.
One-Touch Dialing/Programmable
Like with the redial feature, the handset or base
unit has a memory chip that is capable of storing several
numbers, usually 13 to 18. Each number can be activated at the
touch of a key. This feature is convenient when you cannot
remember a number, are outside or away from a phone book or
need to dial an emergency number in a hurry.
Volume Control
This
feature adjusts the sensitivity of the speaker, ringer and/or
microphone so that you can hear and be heard by the caller. It
is especially useful for conference calls on speaker phones.
Mute/Hold
With this
feature, a switch temporarily disconnects the microphone of
the handset and/or base unit. You can talk to someone else
nearby without your caller hearing your conversation.
Ringer in Base
With this
feature, you can tell when you have an incoming call even if
the handset is not nearby.
Keypad in Base
This
feature allows you to dial from the base to make a call even
if you do not have the handset nearby. It is almost always
found in combination with a speaker phone on the base. This
feature keeps the phone usable when you have temporarily lost
the handset (or your child has hidden it somewhere).
 Photo of a cordless phone base unit with
keypad and speaker phone
|
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. 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.
Extra Battery
Charger
Some cordless phone base units come with a
charger port for an extra battery. This allows one battery to
be charged while the other is in use in the handset. When the
battery in the handset dies, you swap it with the fresh
battery from the base and recharge the dead battery. This
feature allows the handset to be away from the base unit
pretty much all of the time, and means that your handset won't
be out of commission while you recharge a battery.
Hands-Free Headset
Some
cordless phones come with a headset that plugs into a jack on
the handset, and the handset is usually clipped to a belt. The
headset has a microphone and speaker that receive input and
output from the radio components of the handset. With this
feature, you can talk on the cordless phone without holding
it. Your hands are free to do anything else while talking on
the phone, such as type on your computer, do dishes, work in
the garden or play with your children.
Wall Mount
The base units
of many cordless phones can be mounted on a wall so that they
do not take up desk, table or counter space. This feature also
has the advantage of keeping your base unit out of reach of
small children. For example, my son can reach the base unit of
my cordless phone, and his favorite activity is dialing
numbers when we are not looking.
To learn more about additional options click
here, or choose from the map below:
Options
These optional features are usually
available on the cordless phone, but, for the most part, they
need to match your telephone service. Such options include the
following:
- answering machine
- caller ID
- call-waiting
- two-line service
Answering Machine
This is
the one optional feature that does not require a change in
your phone service. Many cordless phones have an answering
machine in the base unit. Modern answering machines are
foregoing the traditional microcassette
tapes in favor of solid-state
memory. With solid-state memory, there are no moving parts
and they can store 15 to 30 minutes worth of messages. Some
machines also allow you to access your messages remotely with
the handset or another phone.
Caller ID
This feature
allows you to know who is calling you before you answer the
phone. The number is displayed on the LCD of the
handset and/or base unit. You must have the caller ID feature
provided by your telephone company for this feature to work on
your cordless phone. There is usually an extra charge for this
service on your monthly phone bill.
Call-Waiting
If you are
talking to one person and someone else calls you, call-waiting
allows you to put the first person on hold and respond to the
second caller or vice versa. Some newer cordless phones allow
you to do this, but you must have the call-waiting service
provided by your telephone company. Again, there is an extra
charge on your monthly phone bill for this service.
Two-Line Service
This
feature allows two phone lines to come into the same cordless
phone. Some of these phones have two different handsets, while
others use one handset to change between phone lines. This
feature has the advantage of using one phone for two lines
(personal line and business line, for instance) rather than
having two different phones. Like the other optional features,
you must have two phone lines installed in your house by your
telephone service provider for this option to work.
In summary, consider the following aspects when looking for
a cordless phone:
- frequency - related to range and security
- analog vs. digital - related to clear sound and
security (DSS
is the most secure!)
- convenience features and options - what you want
in a phone to make it easy to use or to fit your individual
needs
Choose from the map below:
When You Shop
We've created a Cordless
Telephone Feature Comparison chart for you to use as you
research various models. Take it to the store with you and
fill in the blanks for each model you are interested in. You
may also want to keep an additional copy near your desk as you
research models on the Internet.
The feature comparison chart is available to you as a PDF.
You will need the free Adobe
Acrobat Reader to view it.
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.
 Many cordless phone conversations can be
easily picked up by radio scanners
|
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.
Where to Buy
Popular Cordless
Telephones
Here are some of the best-selling
cordless telephone models listed for comparison.
Manufacturers
FAQ
- In the age of cellular phones, why should I buy a
cordless phone?
It is true that cell
phones offer greater mobility than cordless phones, but
cordless phones can give you communication freedom to move
around your house or neighborhood at a much cheaper cost. Cell
phone service is much more expensive than the basic
telephone service used by your cordless phone. In addition,
you do not have to purchase a separate plan to use a
cordless phone as you do with a cell phone.
- Is it difficult to set up a cordless
phone?
No, it's so simple! Here's how you set it up:
- Insert the small end jack of the power
cube transformer into the 9-volt DC jack of the phone.
- Insert the plug portion of the cube into the wall's
electrical outlet.
- Insert one end of the phone cord into the phone jack
of the phone.
- Insert the other end of the phone cord into the phone
jack outlet on the wall.
Lift up the handset, turn
it on and you should hear a dial
tone. You're ready to go!
- Is my cordless phone secure from
eavesdroppers?
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
when it comes to security, and DSS
offers the best protection. Low-end 43-50 MHz and 900 MHz
analog phones are not secure. 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.
- What is the best frequency for a cordless
phone?
Cordless phones operate over three major
frequency bands:
- 43-50 MHz
- 900 MHz
- 2.4 GHz
43-50 MHz band phones have short ranges (about
1,000 ft or 300 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 provides a greater range (5000 to 7000 ft /
1500 to 2100 m), better sound quality and has more channels.
However, 900-MHz signals can be picked up by most
commercially available radio scanners.
A 2.4 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; so
it is more secure than lower frequency models. A 2.4-GHz
cordless phone will be more expensive than lower frequency
phones.
Higher frequencies will provide greater range to your
phone and offer more channels for your phone to use.
- What's the difference between analog and
digital?
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 scanner.
Digital
technology allows the phone signals to sound clearer and
are more secure.
DSS digital technology spreads the digital information in
pieces over several frequencies between the receiver and the
base, thereby making it almost impossible to eavesdrop on
the cordless phone conversations. A cordless phone with DSS
is the most secure.
- How many channels should I have in my cordless
phone?
Each frequency band (43-50 MHz, 900 MHz or 2.4
GHz) can be subdivided into different increments or
channels. The base searches for a pair of frequencies
(channels) within that band 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. The number
of cordless phone channels can vary:
- 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
GHz phones
- How far can my cordless phone handset be away from
its base unit and still work?
The range of your
cordless phone's handset depends upon its radio frequency,
the type of signal (analog or digital) and the presence of
interference. Generally, the higher frequencies will have
more power to transmit and receive, and so will have a
greater range. Digital phones will have clearer sounds over
the same distances than analog phones. Interference from
structures, appliances or other electronic equipment will
affect the range. Under ideal conditions, you can expect the
following ranges:
- 43-50 MHz - about 1,000 ft / 330 m
- 900 MHz - 5,000 - 7,000 ft / 1,500 - 2,100 m
- 2.4 GHz - better range than 900 MHz, but
exactly how much better is not certain yet
If you
use your cordless phone frequently when you are outside or
taking a walk around the neighborhood, you may want to
consider one with an alarm or indicator that tells you when
you are out of the base unit's range.
- What type of battery is best for my cordless
phone?
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.
- Can I operate my cordless phone if I lose my
handset?
This depends upon whether your base unit has
a keypad and speaker phone built into it. The built-in
keypad in the base allows you to dial from the base to make
a call even if you do not have the handset nearby. It is
almost always found in combination with a speaker phone on
the base. This feature keeps the phone usable when you have
temporarily lost the handset.
- Can I have caller ID on my cordless
phone?
Yes, you can have caller ID on some models of
cordless phones. The caller's number is displayed on the LCD of the
handset and/or base unit. However, you must have the caller
ID feature provided by your telephone company for this
feature to work on your cordless phone. There is usually an
extra charge for this service on your monthly phone bill.
Some cordless phones can also have call-waiting or
multiple line services, but your telephone company must set
your house up with these services. Again, there are extra
charges on your monthly bill for these services.
- Can I mount my cordless phone base on a
wall?
The base units of many cordless phones can be
mounted on a wall so that they do not take up desk, table or
counter space. This feature also has the advantage of
keeping your base unit out of reach of small children (my
son can reach the base unit of my cordless phone and his
favorite activity is dialing numbers when we are not
looking).
Cool Facts
- Your cordless phone is a radio transmitter and receiver!
- Most baby monitors and walkie-talkies can pick up phone
conversations from 43-50 MHz cordless phones.
- Digital
spread spectrum (DSS) was invented by actress Hedy
Lamarr.
- Cordless phone components are getting smaller, which
means that more and more functions can be placed in phones
without making them any bigger.
- Memory
chips, instead of cassette
tapes, are now being used on cordless phone answering
machines.
Lots More Information!
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