Perhaps the biggest advances in sound quality, range and security have been in the realm of the new digital cordless phones. Spread spectrum provides noise-free and error-free transmission for the clearest cordless sound. It also provides call security by guarding your conversations from being monitored by another cordless phone user or even a radio scanner.
When cordless phones first hit the market reception wasn't perfect, call security was questionable and range was limited. These phones worked over the same bandwidth that baby monitors and walkie-talkies use. This is why calls placed on these phones often suffered from poor reception and interference.
Cordless phone makers began to counter this problem with phones that operate on efficient, frequencies like 900MHz and 2.4GHz.
The newest, 5.8GHz, is short on call traffic and long on power and speed. Because calls made with 5.8GHz have less traffic to contend with, call clarity and security continue to improve.
All cordless phones use FM frequencies, but there is a difference in sound quality between models. In addition to the new digital technology, having switchable channels can greatly influence your phone's sound quality.
Appliances and other electronic devices can produce radio interference, so many phones can transmit on more than one channel. Better cordless phones have as many as 100 channels. If there is interference on one channel you can switch to another channel to reduce interference. Many new phones switch channels automatically.
Most cordless handsets can be carried anywhere around the house or yard. The maximum rated distance is 1,000' for older cordless phones and up to 7,000' for 900MHz. Some 2.4GHZ, and 5.8GHz phones may be able to reach even further away.
Various environmental factors can reduce the effective range of your cordless phone. Electrical appliances produce radio interference that can reduce the range of the phone. If you are trying to use your phone outside of your home, variations in terrain can also affect the signal from your handset to your receiver. Aluminum siding and wire mesh in walls and floors can also reduce, or block, the range.
The phone industry has come up with several technologies to prevent eavesdropping on cordless phones:
Transmissions are scrambled between the handset and the base, making the conversation unintelligible to people listening in.
This turns the analog (sound) transmission into a digital signal. When the transmission gets to the base, it is turned back into an analog signal. If anyone listens in on the signal, they hear what sounds like a fax machine.
Digital Spread Spectrum
Digital Spread Spectrum provides the most security. Not only is the transmission digital, but the signal is divided between different frequencies. Since most radio scanners only use narrow frequency bands, they never receive the entire content of the phone's digital transmission.