Some thoughts on cordless technology
Radio Devices and waves
-- from our technology guru, David Cook
Cordless phones are radio devices. That is, they work on the same basic principles as AM and FM radios, walkie talkies, cellphones, and even NASA's systems for communicating to the space shuttle or to robot-controlled equipment on Mars. All radio devices depend on sending and/or receiving waves of the electromagnetic spectrum. This spectrum includes such diverse types of energy as X-rays, infrared light, visible light, radio waves, and many other types of radiation.
All electromagnetic waves have a frequency and wavelength associated with them. Frequency is expressed in Hertz, kilohertz (1000 Hertz), Megahertz (1,000,000 Hertz), GigaHertz (1 billion Hertz) or even larger denominations and is a measure of how many crests or valleys of the wave pass a given point each second. So, for example, in a 900 MHz phone, 900,000,000 crests or valleys pass a given point per second. Wavelength is a measure of the distance between crests or valleys and is inversely related to frequency. The higher the frequency, the shorter the wavelength. So you can actually refer to a particular radio wave system by either its frequency or its wavelength and you are conveying the same information. By convention, with cordless phones, we use frequency to divide them into categories.
Waves and range
If you waded through the above two paragraphs, you are probably wondering what the point of this is. The short answer is that frequency (or wavelength -- remember, they tell us the same thing) has a lot to do with effective range. It is probably intuitively obvious that power has something to do with it as well, but let's stick with the frequency issue for the mement.
When I was a kid, I used to be able to pick up far-away AM radio stations late at night. I lived in southern New Hampshire and could easily get New York, Philadelphia, Washington DC and often Chicago. Occasionally, I could even hear stations as far away as Phoeniz, AZ! How was this possible? Because AM radio operates at relatively low frequencies (the high end of the AM dial is only around 1 MHz (1,000,000 Hertz) which is 1/900th as high as a 900 MHz cordless phone, its waves are able to follow the curve of the Earth and travel for long distances.
Now, think about FM radio, which has frequencies in the 100 MHz range. It is unusual to pick up an FM radio station much more than 75 miles from its source.
As you travel up the frequency scale, the ability of radio waves to do anything other than travel in straight lines diminishes, making it harder and harder to communicate around obstacles or the curve of the earth. Microwave communications, for example, only works when the receiver and sender are within line of site of each other. This is why microwave dishes are usually located along abandoned railroad beds, on top of buildings, or mountains: the two dishes need to "see" each other. Please understand that this is not about the power of the signal - we can use microwave signals to send and receive from the moon, which is 240,000 miles away - but rather it is about the radio wave's ability to spread out, go around corners, and permeate an area. The higher the frequency, the worse this capability gets.
So what does this mean to cordless phones?
All things being equal, you can expect worse permormance from higher frequency phones than lower frequency phones inside a building, because the higher frequency waves have a harder time going around obstacles and around corners. This is not the whole picture, however. Higher frequency waves can carry a lot more information than lower frequency waves. This fact means that higher frequency phones can support features such as multiple handsets and signal encryption (for security). In addition, higher frequency waves can punch through some building materials better than lower-frequency waves. This means that, in some buildings, a 5.8 GHz phone will work better than a 2.4 GHz phone.
However, there is another consideration which applies uniquely to 2.4 GHz: because it is widely used in wireless computer networking, if you have both a 2.4 GHz cordless phone and a wireless network, they may interfere with each other. Interference is not guaranteed; if the cordless phone and the network can be set to operate on different channels from each other, then they will not interfere with each other. But this can be easier said than done: even though changing the channel on a wireless network is relatively simple, most cordless phones don't tell you which channel they are on, even if they do let you change it. In addition, your wireless network may work better on some channels than others and you may not wish to change the channel of the network from one which (in the absence of your cordless phone) gives the best reception. Our advice in general, is that, if you have a wireless network, you should avoid other 2.4 GHz products.
Why do we have all these different cordless phone frequencies in the first place?
Early cordless products operated down in the 40-50 MHz range, which was prone to noise, interference from many other wireless products (including CB radios, baby monitors,etc), and had no security. It did not take long for manufactuers to request a new frequency assignment, which resulted in what we consider to be the best performing cordless phones to date: the 900 MHz cordless phones. These phones had phenomenal range, but many also had digital spread spectrum security, which, for the first time, meant you could talk on a cordless phone without fear of being overheard.
For various reasons, including overcrowding of the 900 MHz band, manufacturers have continued to request newer and higher frequencies from the FCC. And, as these frequencies have gone up, cordless phones have developed useful new features such as multiple handset capability. The first such frequency to be assigned after 900 MHz was 2.4 GHz (remember that a gigahertz is a billion Hertz and 900 Mhz is about 0.9 GHz, so 2.4 GHz is about 2 and a half times the frequency of 900 MHz). And, as these higher frequencies were used in large numbers of consumer products, the lower 900 MHz band was abandoned so that now there are almost no 900 MHz cordless phones available. Consumers were told that the increase would result in greatly increased range and freedom from interference, but countless early adopters of 2.4 GHz were disappointed with it and preferred their old 900 MHz phones.
So the next increase was 5.8 GHz, more than twice the frequency of 2.4 GHz. The same claims were made for 5.8 GHz that had been made for 2.4 GHz. Customers have had mixed results with 5.8, but, at the very least, because of the lack of network intereference from the 5.8 GHz products, customers have generally had better results with them than with 2.4 GHz. However, some users have reported that 5.8GHz has less range than 2.4 GHz (which, of course, conforms to our discussion about frequency and range).
The most recent new frequency assignment to come to consumer cordless products is, for the first time, lower: 1.9 GHz, using an encryption technology related to that used by cellphones and referred to as DECT. We're quite excited by DECT, because it really seems to be a good balance between range and features. DECT products can have multiple handsets and security, but can also permeate an area with signal the way lower frequency products did. And their sound quality is the best I've heard so far.
So what do I buy?
To make a good choice of cordless phone technology, you need to be clear with yourself about what is most important to you, because some compromise will likely be needed.
5.8 GHz phones have proven to be secure, have good sound, and adequate range for normal-size houses and small business applications. 5.8 GHz is also where the majority of new phones and new features are to be found.
2.4 GHz has become the low-cost alternative to 5.8 GHz. The range is generally somewhat better than 5.8. However, if you have a 2.4 GHz wireless network, you may wish to avoid 2.4 GHz cordless phones. Also, if you take a look at our site, you'll notice that the majority of multi-handset cordless and nearly all 2-line cordless products are in the 5.8 GHz range, not 2.4 GHz.
If you want a very inexpensive basic cordless phone, 900 MHz has now become the low-cost product in cordless, although there are only a few products left on the market. You can see what we have by clicking on the 900 MHz cordless link at upper left on this page.
If super range is a must (usually in commercial installations or very large houses) you will want to check out the 900 MHz high-powerwed Engenius Longrange Cordless phone; this product supports up to 9 handsets and works well in large houses, warehouses, and other difficult commercial premises.