2.4 GHz Cordless Phones
What are 2.4 Ghz Cordless Phones?
As the name suggests the 2.4 GHz cordless phones use frequency in 2.4 GHz range. FCC (Federal Communications Commission) has allocated the frequencies between 2.4 GHz and 2.4835 GHz, with a channel spacing of 5 MHz. for 2.4 GHz cordless phones.
The digital cordless phones in 2.4 GHz bands using digital spread spectrum (DSS) techniques provide larger range over analog phones. This is because the FCC allows DSS phones to transmit up to one watt of power while analog phones are limited to one milliwatt (0.001 watt). Thus DSS phone can transmit power one thousand times more than incase of analog phones using the same frequency. The DSS based phones claim to have range as large as upto 1 mile under suitable conditions.
A 2.4 cordless is considered to be more secure than phone in 900 MHz band as the frequency used is above the frequencies that can be picked up by most commercially available radio scanners.
Disadvantages Of 2.4 GHz Cordless Phones
The 2.4 GHz cordless phone frequencies are shared with Wi Fi or WLAN or 802.11b/g wireless networks. Two methods used for radio frequency modulation in 2.4 GHz cordless phones are frequency-hopping spread spectrum (FHSS) and direct-sequence spread spectrum (DSSS). Most phones use FHSS, where the frequencies hop one to another across the entire 2.4GHz spectrum. The phones using DSSS typically have a "channel" button on the phone allowing users to manually change the channel.
Wi Fi uses direct sequence spread spectrum (DSSS), which transmits within approximately one third of the 2.4 GHz spectrum. Thus there are chances that two systems may interfere with each other. It has been noticed that in few cases the cordless phone due to its high power can corrupt a WiFi transmission. Thus it will be safer not to use these phones in close proximity of WiFi devices. However, for the cordless phone is using DSSS the channel used by it may be configured so as not to overlap with Wi Fi, to eliminate interference.
Some phones such as the Panasonic GigaRange phones use two different bands for sending and receiving wireless signals. 2.4 GHz frequency is used for transmitting from the base to the handset, and uses a 900 MHz frequency is used for transmission from handset to the base. This allows duplex (two-way conversation) sound with virtually no echo and enhanced distance performance.
