Home

Phone System

More on Phones

Cordless Phones

More on Cordless

More on Cordless

More on Cordless

More on Cordless

How PBX Works

How PBX Works

 

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.

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.


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.

Features

Cordless phones have many of the same features as standard telephones, and there are many models, offering lots of different features.

Major Features
Reme

Duplex Example

Base:

.
44.32 MHz transmitter  .49.28 MHz receiver

Handset:

.
49.28 MHz transmitter .44.32 MHz receiver

mber 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 of cordless phone channels can vary as follows:
10 to 25 channels - 43-50 MHz phones, some inexpensive 900 MHz phones

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.

 
Keywords :- phone systems for small business,small business phone systems,small business telephone systems,virtual phone systems,small business telephone system,small business phone system,office telephone systems, pbx phone systems,telephone answering systems,business telephone systems,virtual phone system,internet phone systems,business telephone system,small office phone system,voip phone systems,multi line phone systems,office telephone system,office phone systems,business phone system uk,voip telephone systems,ip phone systems,business phone systems,office phone system uk,digital phone systems,voice over ip phone systems,office phone system,pbx phone system,internet phone system,voip phone system,automated phone systems,ip telephone systems,used phone system,phone system supplier,business phone system,telephone systems,cheap phone system,used phone systems,ip phone system,home phone systems,refurbished phone system,hotel phone system,pbx telephone system,phone system software,cisco phone system,best phone system,new phone system,centrex phone system,norstar telephone systems,panasonic telephone systems,automated phone system,voip telephone system,meridian telephone systems,nec phone systems,northstar phone system,nortel phone system,phone systems,cisco phone systems,home phone system,nortel norstar phone system,asterisk phone system,toshiba phone systems,used telephone systems,norstar phone systems,pc phone system,multi line phone system,panasonic phone systems,avaya phone systems,avaya phone system,norstar telephone system,wireless phone systems,norstar phone system,nortel phone systems,cordless phone systems,bruce municipal telephone system,
meridian phone system,telephone entry systems,meridian telephone system,phone system,ip telephone system,nortel telephone systems,merlin phone system,4 line phone system,wireless phone system,phone system installation,voice over ip telephone systems,2 line phone system,toshiba phone system,samsung phone system,partner phone system,mitel phone system,nortel telephone system,phone system repair,nec phone system,telephone answering system,panasonic phone system,telephone system,nec telephone systems,nortel meridian phone system,meridian phone systems,key telephone system,telephone entry system,panasonic telephone system,phone answering system,telephone headset system,4 line cordless phone system,phone systems toronto,digital phone system,expandable phone system,cordless phone system