| A cordless telephone is an electronic | | | | range. Even the best of the cordless |
| telephone that comprises of a wireless | | | | telephones fail to match the audio quality |
| handset and a base unit. Communication is | | | | that a high quality phone wired to a good |
| carried out between the handset and the base | | | | telephone line provides. |
| using radio waves. The wireless handset can | | | | |
| be operated only within a fixed range from | | | | Sidetone (echo of voice heard in the speaker |
| its base unit. The range of operation is | | | | of the receiver), disturbing constant |
| generally within 100 meters. The base unit | | | | background noise that is due to the cordless |
| needs electricity to power it. Batteries are | | | | system, and inability to obtain a full |
| used to power the cordless handset. Placing | | | | frequency response that is available in a |
| the cordless handset in the cradle in the | | | | wired phone are few of the reasons for a |
| base unit recharges these batteries. A period | | | | not-so-good audio quality. Rare exceptions, |
| of 12 to 24 hours is required for recharging | | | | obviously, always exist that sound |
| the batteries. | | | | unbelievably similar to a wired telephone. |
| | | | But even these are considered as `fluke` by |
| With features like cell handover, data | | | | most industry standards. |
| transfer and international roaming (on a | | | | |
| limited scale), the once clear-cut line | | | | Higher frequency is now being used in other |
| between mobile telephones and cordless | | | | home products like the microwave oven, Baby |
| telephones has now been blended by the modern | | | | monitor, Bluetooth, wireless LAN, etc. Thus, |
| cordless telephone standards. | | | | cordless telephones using higher frequency |
| | | | may face interference from signals from these |
| Frequency bands have been assigned in each | | | | devices. |
| country for cordless telephones. | | | | |
| Advertisements by manufacturers claiming that | | | | Eavesdropping is a constant security threat |
| there is an improvement in audio range and | | | | for analog telephones. Any one with a radio |
| quality with higher frequency are a common | | | | scanner and within range can pick up these |
| sight. But that is not the case. Actually, | | | | signals and listen to conversations. Modern |
| higher frequencies have been seen to exhibit | | | | digital technology is thus being used to take |
| worse propagation in ideal case. There is | | | | care of this kind of unauthorized access. |
| also a tendency for the path loss to increase | | | | |
| with higher frequencies. Locally varying | | | | DSS (Digital Spread Spectrum) makes use of |
| factors such as antenna quality, signal | | | | frequency hopping, i.e. spreading up of audio |
| strength, the modulation method being used | | | | signal over a wider range in a pseudorandom |
| and interference are more influential than | | | | fashion. DSS signal sounds like noise bursts |
| other factors. | | | | to a radio scanner or any other analog |
| | | | receiver. This signal makes sense only to |
| With Landline telephones working on a | | | | that base unit which has the same |
| bandwidth of about 3.6 kHz (a small fraction | | | | pseudorandom number generator as the cordless |
| of the frequency that a human ear can | | | | handset. Each time the cordless handset is |
| interpret), the transfer of audio is carried | | | | returned to its cradle, a new unique |
| out with an audio quality that is just enough | | | | generator is chosen from thousands of |
| for the parties to communicate each other. | | | | options. |
| Because of this limitation in the design of | | | | |
| the phone system itself, it is not possible | | | | DSS generates a signal spread that leads to a |
| to improve the audio quality beyond a | | | | kind of redundancy, which gives rise to |
| particular limit in cordless telephones. | | | | increased signal-to-noise ratio. It also |
| | | | leads to increase in signal range and |
| Most of the good-quality cordless telephones | | | | decreases interference susceptibility. It is |
| try transferring the audio signal with lowest | | | | easier to use this kind of wide-bandwidth |
| possible interference and greatest possible | | | | security option with higher frequency. |