Cordless phones are often
painful to install and troubleshoot. Making them work right is time consuming, expensive and frustrating.
Sometimes we just can't make them work right.
Diagnosing why the cordless phone
doesn't work isn't straightforward, mainly because we don't have
diagnostic tools (like we do for wired phones). The cellular companies
have plenty of dead spots and they have the tools to diagnose the
problem (a van full of radio receivers and transmitters, and spectrum
analyzers). There are still plenty of cellular dead spots, mainly
because they can't find a place to put up another tower, or they don't
feel it's worth the expense.
In an office, factory or home, we have
all of the same problems that the cellular companies have without the
resources of a cellular company. These problems also affect Wi-Fi and
RFID applications. The problems are exactly the same, and
sometimes other stuff is the problem (interference).
This is what effects the RF signal:
- Frequency (lower frequencies
like 900mhz penetrate walls better, 1.9ghz DECT has the least
interference from other type of wireless devices, and 5.8ghz
doesn't penetrate walls well)
- Distance from base (antenna) to handheld
- Number of partitions (walls,
floors and ceilings)
- Material of partitions
(drywall, concrete, rebar, aluminum, steel)
- Stuff in the way (trees
outside, big metal equipment inside)
- Interference - Other devices
using the same frequencies (unlicensed devices all
share the same channels in the same frequency bands)
There is no question that using 900mhz
phones will give you the best penetration of walls and possibly the best
distance. I don't know why, but
900mhz isn't sexy, and it's not used much these days. Most manufacturers make the new 1.9ghz (DECT), 2.4ghz or 5.8ghz phones.
The newest frequency band used for
cordless phones in the US is 1900mhz (1.9ghz), usually called DECT
because of the digital standard used in the communications. DECT has
been used in Europe and Asia for some time. The FCC decided
to clear out the frequencies that were used for European DECT, and
allow those phones to be used here.
DECT is probably the best choice for basic home or
office cordless phones since there's no interference from baby
monitors or Wi-Fi on that band right now. 1900mhz doesn't penetrate
walls as well as 900mhz phones, but it's a lot better than the 2400mhz
(2.4ghz) band because there's no interference (and penetration is a little
900mhz phones share unlicensed
channels with other RF devices like baby monitors, wireless cameras,
RFID and other phones. Since 900mhz isn't sexy, there's not much stuff
using that band any more. While most of these unlicensed devices are
designed to detect which channels are in use and pick a different one,
some do a better job than others. Older cordless phones might not even
try, and jump on a channel and go. Some of them might have a channel
button, so you can manually change the channel during a conversation.
Not good in a business environment.
2.4ghz is the most crowded band... with
2.4ghz phones, Bluetooth and Wi-Fi being very popular. There's even 2.4ghz
wireless broadband using directional antennas from a tall tower
directed at homes and offices, and in some areas there's
free neighborhood Wi-Fi where the 2.4ghz Wi-Fi signal is all over the place.
What's worse, some newer Wi-Fi devices
"bond" together more than one channel so they'll go faster
That's a nice idea but since there are a limited number of channels,
that can really cause interference with other 2.4ghz non Wi-Fi
devices, or even a Wi-Fi device at the business next-door. Cordless
phones can kill the Wi-Fi network, the Wi-Fi network can kill the
cordless phones, and it's pretty hard to know what's really going on.
If you use a 2.4ghz cordless phone with
a Bluetooth headset (which is also 2.4ghz), and you have a Wi-Fi B
router (2.4ghz) for the Internet, and maybe 2.4ghz baby monitor or
wireless camera, none of these things are going to work well!
It's even worse when a neighbor has this stuff in their home or
office, and it's screwing up your wireless devices.
If you use a Wi-Fi 802.11N
router, which works on 2.4ghz and 5ghz, and Wi-Fi N cards
for your computers, you can usually tell the router to just use the
5ghz band which will avoid interference with 2.4ghz phones and RFID
equipment. Older W-Fi B wireless cards in laptops won't work in
that situation (the 2.4ghz band was included in N routers
to make them compatible with the older, slower B cards). If there are no guests on the wireless network
that have to use B, this is a good way to
The blue lines on the graph indicate occasional transmissions and
their signal strength. The red lines indicate constant
transmissions. In the above illustration, it's probably an
audio device like a cordless phone, wireless speaker or audio baby
monitor. It would clobber any Wi-Fi device using Channel 1!
The screen shot below shows a 2.4 ghz device, like a wireless security camera
or wireless baby monitor, with a camera that needs a lot of bandwidth.
Again, the red indicates that it's transmitting constantly:
Many wireless devices (like cameras and wireless speakers) have a switch to let
you choose maybe one of three "channels" to prevent interference. When you
switch to a different channel, the above interference would move to some other
Wi-Fi channel. As you can see it's really clobbering Channel 11 here!
All Wi-Fi access points and routers will let you change the 2.4 or 5.0 ghz
channels that it uses. Sometimes they make a good guess themselves, but if
things are going downhill you may need to set the channel yourself.
Note that there are only three Wi-Fi 2.4 ghz channels that don't overlap with
another channel, even though there are 11 channels. Channel 1, 6 and 11 are the
only ones that don't overlap. Sometimes you've just gotta do what you've gotta
do at a particular premise, so you could choose 3, 8 or whatever if it gives you
The $199 USB Wi-Spy is a Spectrum Analyzer just looking at RF (radio
receiver), not specifically Wi-Fi. You still need the Wi-Fi adapter in your
laptop to overlay the Wi-Fi channels.
If you use a DECT (1.9ghz) phone with a
Bluetooth headset (2.4ghz), and an N router (5ghz) and a 900mhz baby monitor,
you probably won't have any interference between the devices. If you're purchasing
cordless devices it can be well worth your time to think it through
before you buy the stuff, rather than spending time troubleshooting
and returning stuff afterwards.
If an office backs up or is next door to another
business, you could have interference from their wireless stuff that you
have no way of knowing about, unless you go next door to ask them about
wireless stuff they use. Having a next door neighbor with welding
machines that put out garbage over the entire frequency spectrum could
make you chase your tail for months. The phone lines for your business could
even be running right past those welding machines on the way to your
Engenius, the longest range US cordless phones
made, use the 900mhz band. Both the base station and handhelds have antenna
connectors to allow maximum coverage. Somehow, this manufacturer's
phones seem to have more transmit power than consumer cordless phones.
Some users plug the handsets into antennas in cars or trucks to be
able to answer phones while they drive around a large property.
HERE to see the 1-Line and 4-Line Engenius long range cordless phones
Most consumer phones don't have antenna
connectors, especially on the handsets. In most cases, a taller
antenna works better on the handset than a smaller antenna. If the
base station has an antenna connector, technically speaking you can
use an antenna splitter to mount two antennas - like on each side of a
concrete wall to cover two areas with one base station. Practically
speaking, you'd need to get a splitter for the correct frequency band,
use as little of the correct low-loss coax cable as possible, have the
right connectors on the cable (or adapters), and you still end up with
less than half the power to each antenna (due to losses in the
splitter and cable). Will it make a difference? Maybe, but it's
expensive to find out.
If you mount an antenna outside, you
definitely need a lightning protector between the antenna and base station. It would have to be
grounded well to help save the base station in a lighting storm.
Very high power cordless phones are
available in other countries, and some people illegally
sell them here in the US (usually marked "For Export").
Since most of them transmit on US amateur radio frequencies, you can
count on the FCC being notified of their illegal use almost immediately
(by an amateur), and a pretty big fine if they aren't shut off after
the FCC comes calling. If it transmits on some national defense
frequency or you interfere with aircraft communications, it could be
more than a fine.
Most cordless phones connect to a
standard analog phone line, or analog extension port. Some phone
system manufacturers have their own cordless phones made to plug into
a digital extension port, giving you some additional features that
work with that particular phone system. Those types of phones are
fairly tightly integrated to that particular phone system, which is
good. Some also offer a cell based approach, where you can put
multiple cell type base station sin the business for better coverage.
No matter what you do, there will be a
high cost of maintenance on these types of cordless phones. No other
cordless model/brand will work with that system, so you have to repair
or replace the cordless handsets with the same make/model. No matter
what, a cordless phone will never last as long as a desk phone - which
is seldom (if ever) dropped on a floor, sat on or stepped on. Even the
most careful employee will destroy many cordless phones over the life
of a desk phone, but the improved productivity should make up for that
additional maintenance expense.
One of the biggest problems with
selling your customers accessories for their phone system is that
the accessories can easily cost more than the KSU. Phone systems
have generally gotten so cheap that adding $1,000 worth of
accessories to make it work for the customer's application, whether
it's a cordless phone from the phone system's manufacturer or Loop
Current Regulators for each phone line, the customer can easily
think you're nuts or ripping them off for the accessories.
In the case of a cordless phone - in many
cases the productivity increase will easily pay for the accessory, but
that's a hard thing for some customers to keep in mind when they're
writing the check. Today, with one person doing multiple jobs in many
cases (due to layoffs/the economy), increasing productivity may be the
only way for the company to survive, and a cordless phone may be a very
Whatever kind of phone you
buy, figure it will be discontinued pretty quickly. If it's a business
type phone, they'll have a longer life and they might be around on the
refurbished market for a while. If it's a consumer cordless phone or
system (like AT&T, V-Tech, Uniden, Panasonic, etc.), it will probably be
discontinued pretty quickly. If you need repair, replacement or an
additional handset for one of those consumer type cordless phones -
you're probably screwed. They seem to change consumer / retail models
every few minutes. Your choice at that point is ebay, or going with
the latest greatest system (that's probably not compatible with the
"Cell type" cordless phones
can be the only way to get cordless phones to work in a particular
facility. This lets you put
several base stations around the building / grounds, giving you a better chance
at covering the whole place.
Multiple base stations aren't always a
fix for bad reception. You have to place the base stations so they
have a clear shot, with as few partitions as possible between the base
and cordless handset.
You also have to figure out what the
floors and partitions are made of, and plan the placement of the base
stations so the radio signals will be able to reach the handset.
A solid metal wall or floor is enough
to stop RF cold. A concrete wall or floor with rebar, metal rods
running through the concrete to give it more strength, will stop most
of the RF.
Wooden studs and drywall stop some of
the RF. Metal studs and drywall stop more.
Big metal machines or metal warehouse
shelves between the base and handset will have a big effect on
coverage. Placement of the base station (if it has a built-in
antenna), or the antenna connected to the base station is critical in
most environments. Most antennas radiate a pattern that will let the
antenna be installed upside down from the ceiling. Some antennas are
made for ceiling mount. If you have multiple base stations, placement
of the antennas so they don't interfere with each other is important.
You may need directional antennas in some cases, which give you much
greater coverage in a fairly narrow path (handsets or base stations to
the side or rear won't see this antenna). They are particularly useful
It's probably sounding like a lot of
work to install cordless phones in an office or shop? It is. The labor
to find the right base station locations can be substantially more
than running the cable for a wired phone. It's all knowledge gained
from previous installations, and trial and error. No two premises will
be the same. There are different walls, floors, distances, and stuff
in the building. Making cordless devices work right is nowhere near as
easy as installing cabled phones or computers.
If you have to install cordless
equipment before all of the furnishings, fixtures, walls or equipment
is in-place, there's a pretty good chance you'll have to make some
changes after the customer moves in (which will be harder because all
the stuff is in the way). There's no way to anticipate the costs of
making the cordless stuff work. Some of the installations will be
easy. Some will be hard.
The hardest wireless problem to
troubleshoot is interference from other RF devices. You can see the
walls and equipment, but you can't see, smell, hear or feel RF.
There's a pretty good chance that the premise has some other wireless
stuff, and some of it can be on the same frequency band as the
equipment you just installed. Maybe your stuff is installed first, or
maybe the other stuff was installed first. It doesn't matter, because
now both sets of wireless equipment might not work.
Asking the customer what other wireless
devices they use would help, but in many cases the customer won't
remember the wireless cameras, RFID or Wi-Fi stuff that's in-use. The
customer can't see, smell, hear or feel the RF, either.
The only real solution to tracking down
RF interference on the same frequencies is a Spectrum
In many cases, the customer just
doesn't want to pay for the time it takes to install cordless phones
so they work right. They go out and buy phones at the Office Biggie
store, hopefully with a money back guarantee (which is good since it's
not a sure thing that they'll work). In a small office, that would
probably work OK and it's probably the only way to make cordless
phones affordable if you don't take productivity gains into
consideration - which is why they want cordless phones in the first
There's no way a phone system vendor can compete with the
Office Biggie stores selling consumer cordless phones. The only way to
install cordless stuff is T&M. You have to run the station cable
for the base, which might take several tries. Making yourself a two
hundred foot mod cord for testing from the nearest spare pair isn't a
bad idea. There's a small possibility it just won't work in that
particular premise no matter what you do.
customer can buy all-risk insurance coverage on the cordless phones
(like they offer for cellular phones), that's a good idea.
Just by virtue that
it's carried around, dropped and lost, no cordless phone will hold up
as well as a desktop phone in the long run, and some of them are very
expensive to repair or replace. Worse than that the
manufacturers often discontinue a model making repair or
replacement impossible. Maybe business insurance would pay for replacing it with
the current model?