NEW 5.8 GHz cordless phones: are they better than 2.4 GHz?
by Jim Hanks
Just when you thought you had a high-end cordless phone, the frequencies
got higher. But are the new 5.8 GHz phones better than 2.4 GHz and 900 MHz models?
Or is this just the latest marketing scheme? After reading this article, which
includes some technical background on cordless phones and the frequencies they
use, you will have a better idea of whether or not a 5.8 GHz phone is a wise
investment for your home or office.
Why higher frequencies can be better
Many people think that just because a phone uses a higher frequency its range
will be better. In reality, the physics of wireless technology is a little more
complicated. There are 3 main factors that affect the quality and strength of
a cordless phone's signal: traffic, how the frequency handles obstructions,
and output wattage.
Using a specific range of frequencies assigned by the Federal Communications
Commission (FCC), cordless phones send and receive calls with technology similar
to that of an FM radio. Unfortunately, many other devicesincluding cellular
phones, ham radios, walkie-talkies, baby monitors, and pagersare also
constantly transmitting wireless signals in the air around you. When any of
these devices uses the same frequency or bandwidth as your phone, interference
This is where the FCC plays an important role. In order to prevent interference,
the FCC determines which devices are allowed to transmit within specific ranges.
When a range reaches its traffic capacity, the FCC will usually open up another
range of frequencies for use.
Early generations of cordless phones used the 46-49 MHz bandwidths. Since anything
that emits low-band interference in this range, devices such as refrigerators,
TVs, and computers diminished the clarity and range of cordless conversations.
Additionally, baby monitors and low-band pagers also crowded these same frequencies.
So, as more people bought 46-49 MHz cordless phones and interference became
even more prevalent, the FCC opened up the 900 MHz range.
With their improved range and clarity, 900 MHz phones became a standard household
appliance and subsequent traffic increased. At their peak, 900 MHz phones often
allowed users to overhear conversations from their neighbors phone. Due
to this congestion, the FCC opened up yet another range of frequencies: the
2.4 GHz band. Though this frequency was new for phones, the 2.4 GHz band was
also being used for wireless LANs. Additionally, microwave ovens emit transmissions
in the 2.4 GHz band. Enter the 5.8 GHz band. As the most recently adopted cordless
phone frequency, the 5.8 GHz band offers the least interference.
How the frequency handles obstructions
When dealing with longer distances between a transmitter and a receiver, a lower
frequency will usually provide better range because the signal's wavelength
is longer and can travel around obstacles.1 This
is why analog cellular phones (which use the 800 MHz frequency band) often have
greater range than PCS systems (which use the 1900 MHz frequency band). If such
logic stands, one would assume that a cordless phone utilizing the 900 MHz band
would perform better than one using the 2.4 GHz (or 2400 MHz) band. Not so.
When a system is employed in a confined space such as an office or home, many
obstacles such as office equipment, walls, and doors obstruct the handset-to-base
path and prevent signals from circumnavigating barriers like they could in a
less densely occupied area. So what becomes important in these cluttered spaces
is a signal's ability to be deflected and then to find the reception antenna.
Low-frequency signals in the 46-49 MHz range have wavelengths of 18 feet, so
they must be repeatedly deflected to cover an area. As a result, these signals
will often lose their strength before finding the reception antenna. Because
signals in the 900 MHz range have wavelengths of only a few feet, it is easier
for them to quickly cover an area more completely.
If the above explanation confuses you, think about how a child would fill in
a square with a crayon: quick side-to-side movements within the square do the
job much faster than if the child were to wait until he or she hit an edge before
Wavelengths (or crayon strokes) for 2.4 GHz phones are even shorter than 900
MHz wavelengths and consequently cover a room quicker. Signals in the 5.8 GHz
band cover an area even faster.
To keep neighbors from constantly hearing each other's conversations, the FCC
initially limited the output wattage for cordless phones to just .001 watt.
But when digital and spread spectrum technologies (SSTs) made eavesdropping
a less valid concern by scrambling signals or dividing them across multiple
bandwidths, the allowable wattage for cordless phones was increased to 1 watt.
This action made for clearer calls and increased a cordless phones range
three- to fourfold. Meanwhile, the increased wattage covered up the fact that
higher-frequency signals require more power to transmit.
When 5.8 GHz phones were introduced, the allowable wattage was not increasedand
here is where the buyer must beware. Because transmitting signals at a higher
frequency requires more power, some 5.8 GHz phones use the new frequency only
for the base-to-handset transmission. Then, to make sure a handsets battery
has a reasonable life, handset-to-base transmissions are sent on the older 2.4
What's the bottom line?
Due to the multiple factors involved, the range and clarity of cordless phones
vary. In general, you can expect better clarity as you move from 46-49 MHz models
(which are overcrowded with baby monitors and walkie-talkies) to 900 MHz models
(which most homes use for cordless phones) to 2.4 GHz models. The primary benefit
of 5.8 GHz models is the avoidance of interference with 802.11b wLANs and microwaves.
If interference is your primary concern, make sure you purchase a fully 5.8
GHz phone.2 Otherwise, a dual transmission phone
will give you better battery life.
As for range, here are some average maximum distances for the different technologies.
Keep in mind that these numbers are very subjective and depend on factors such
as obstructions, frequency interference, transmission technology, and even weather.
The higher figure listed assumes ideal conditions are present.
46-49 MHz - 40 to 250 feet
900 MHz - 75 to 400 feet
900 MHz w/spread spectrum - 200 to 1500 feet
2.4 GHz w/spread spectrum - 300 to 2000 feet
5.8 GHz w/spread spectrum - 300 to 2000 feet
In addition to their other advantages, the 2.4 GHz and 5.8 GHz frequency bands
are above the range that most scanners can intercept, making it much more difficult
for eavesdroppers to listen to your conversations.
In the end, if you're willing to shell out a few extra dollars for a 2.4 GHz
phone, you'll get much better call clarity, better security, and increased range.
And if you covet the newest of the new, a 5.8 GHz phone will also avoid interference
with your microwave and wLAN.
1 An interesting note: The size of a signal's
wavelength also determines the required size for the antennae (both the base
station's and the handset's). The wavelengths of 46-49 MHz signals are 18
feet. In order to "catch" the signals, both the base station and
the handset need antennae that are 2-3 feet in size. When 900 MHz phones were
introduced, antennae were downsized to just 6 inches since the wavelength
of their signals was only a foot long. 2.4 GHz and 5.8 GHz phones are even
more portable and user-friendly, as their antennae are only a couple of inches
2 Although it will be some time until
it is introduced, a protocol using 5.8 GHz technology is in development. This
new protocol, 802.11a, will be able to send high-quality video. It will also
interfere with the new phones.