About Radio Repeaters/Signal Boosters
Extending the range of your cell phone
or two-way radio
A radio repeater can
greatly increase the effective range of a radio or cell
As amazing as radio devices
are, they all have finite range, and sooner or later, we'll find
the device we're relying on has lost its signal.
At times like that, and whether
it be with Wi-Fi, walkie-talkies, or cell phones, some type of
signal booster, extender, or repeater will probably add to the
effective range of your device. In such cases, a
repeater/booster/extender might quite literally be a life-saver.
Elsewhere we review specific
products for a laptop's Wi-fi signal and for most cell phones; this page here gives you background about how the
devices work. Understanding their operation can help you
choose the best devices and then use them to best advantage.
What a Radio Repeater Does
In its simplest form, a
radio (or television or any other type of signal) repeater
simply takes a weak/distant radio signal, amplifies it, and
rebroadcasts it again.
This means that the
effective range of a device is increased.
Repeaters can do much more
than this, and there are some complexities in what they do and
how they do it, so please continue reading through this
The Growing Need for Radio
There are many reasons why
radio repeaters are increasingly necessary.
1. An evolution to
higher frequency services with shorter range and less signal
Way back in the early days
of radio, frequencies were very much lower than they are today.
These lower frequency
signals had greater range and penetration. They could penetrate
buildings, and they could curve around the earth's surface,
be bounced off the atmosphere and back down to ground again.
A good example of such
signals are those found on regular AM radio (frequencies in the
0.5 - 1.5 Mhz range) and those used in shortwave broadcasting
(2.3 - 25.8 MHz), much amateur radio, and commercial HF (high
frequency) radio transmitters (frequencies in the general range
of 3 MHz - 30 MHz).
As you may know from your
own experiences, AM radio stations can have a range of 100 miles
and more, and if you've ever listened to shortwave radio
stations, you'll know they can sometimes reach all the way
around the world.
And, as you also know, you can generally pick signals up inside a
house as well as outside.
By comparison, think now of
an FM radio station (88 - 108 MHz, in the VHF frequency band) or
a television station (ranging widely from 54 - 806 MHz).
As you know, their range is much shorter, and the quality of the
signal is much more sensitive to whether you are trying to
receive it inside or out (think rabbit ears vs an outside
antenna for your television set).
As radio technology
improved, the frequency of radio transmissions steadily
increased. There were (and still are) a number of valid
reasons for this. Higher frequencies have more 'bandwidth'
to carry more information in a signal, whether this information
be better quality stereo audio (ie in FM radio) or high
television (compared to low definition black and white), or data
at increasing speeds (eg with a cell phone).
In addition, as lower frequencies
became 'used up' - in the sense of all available frequencies
being allocated for various different uses, there literally was
nowhere to go except 'up', going to higher and higher
frequencies, which typically have a range limited to 'line of
sight' only and which are increasingly sensitive to all types of
obstruction between the transmitter and receiver.
These days frequencies are
in use all the way up to about 6.0 GHz, even on such low-cost
and seeming low-tech devices as cordless phones (some of which
use a 5.8 GHz frequency).
As an aside, there is sort
of an upper limit to how high radio frequencies can go. At
a certain point (around about perhaps 300 GHz), they start to
evolve from being radio frequencies to infra-red frequencies,
and their range and ability to penetrate objects drops down to
an impractical level (put a piece of paper in front of your
infra-red remote control to see what I mean).
2. Congested radio waves
require stations to share frequencies more ways by becoming less
powerful, with shorter ranges
One of the key concepts of
making modern cell phone service a viable concept is by limiting
the size of each 'cell'. In the early days of analog cell
phone service, a cell might be some miles in diameter, and only
capable of handling (say) 50 calls simultaneously. It was
quite common for one's phone to have to switch to a more distant
cell (with a poorer quality signal), or not to be able to get
service at all, due to congestion in the cell you were in.
Nowadays, think of
situations such as a ball game or large convention, where you
might have 50,000 - 100,000 people, all with cell phones, and
all packed together tightly in a radius of perhaps a quarter mile. That is an
extraordinary density of users, and they all expect reliable
service and the ability to make and receive calls.
Part of the solution has
been to make each cell very much smaller. Now you can have
very tiny cells with coverage of perhaps only 100 yards (or even
compared to other cells that might extend 10 miles.
3. A growing demand for 100%
These days cell phones are
displacing regular wired phones, and in general are becoming
increasingly central and essential to our every-day life.
And - perhaps paradoxically
- the better that cell phones get, and the more reliable they
become, complete with ever-growing coverage, the more we expect
and demand of them. At the same time, the smaller the
phone, the smaller its antenna, and the less effective/efficient
it becomes at sending and receiving calls.
When cell phones were still
somewhat experimental, we were more forgiving of them, of their poor
quality, and of the dropped calls we used to suffer. Now we expect - we demand
- 24/7 perfect coverage, and everywhere.
4. Other devices need
repeaters and boosters too - Wi-fi
Wi-fi service is another
part of modern life that is increasingly being taken for
granted, but which is very range challenged. The standard
Wi-fi specification anticipates a range of about 100 ft or even
slightly less indoors, depending on how many obstructions such
as walls are between the router and the device.
Furthermore, as Wi-fi signal
strength weakens, its data speed reduces. That was once
not a problem, when the internet speed it was connecting to was
perhaps only 500kb/sec or so, but now that internet speeds
beyond the Wi-fi router are much higher, a slow Wi-fi speed can
materially impact on our internet experience.
5. Still more devices -
GMRS and other amateur radio services
GMRS radio service has
become affordable and commonplace, and the FCC seems likely to
remove the requirement to license GMRS radios - a requirement that
99% of GMRS radio owners have been ignoring for some years now
Unfortunately, the FCC is
also probably going to reduce the power that portable GMRS
radios can have down from 5 watts to only 2 watts.
GMRS radio is designed to
work with repeaters. Perhaps the latest FCC changes will
accelerate a need for repeaters here too.
Simple Range Boosting Without a
The simplest way to boost
the range of any device is to replace its internal antenna with
an external antenna. The external antenna may be a more
efficient antenna, better able to send stronger and receive
weaker signals; it might be directional, sending and receiving
more strongly in a particular direction; and/or it might be in a
better location than the antenna on the device itself.
This is of course not a
repeater per se, because it is not rebroadcasting anything.
It is simply an external antenna, or perhaps described as a
'signal booster' or 'range extender'. But if it gives you
the extra reception you need, who cares what it is called!
How a Cell Phone
Repeater/Signal Booster Works
In its simplest form, a
true repeater/signal booster (as compared to the simple enhanced
antenna discussed above) simply receives a weak radio signal and
then retransmits it more strongly, enabling the signal to travel
There is actually a lot more
to the process than this first one sentence description, so
let's look at in step by step form.
needs to have a better aerial/antenna than the devices it will
be repeating/boosting the signal for. If it is no better
at receiving a signal than the device it is repeating the signal
for, it would not add any extra
range or value, because it will fail to receive a usable signal
at the same time the unit is is supposed to help does too.
So the first key ingredient
of any type of repeater/booster system is a good antenna to
receive signals from the far away station.
1. Receiving a Distant
The first part of providing
a repeater or signal booster service is to be able to better
receive the distant signal than the device it is supposed to be
augmenting. If you think about it, you'll realize the
essential nature of this - if the so-called repeater has no more
receiving range than the device that will rely on it, then it
too will stop receiving at the same range from the distant
transmitter, and therefore it will provide much less practical
benefit than if it had a better receiver capability than that
belonging to the boosted unit.
The ability of a unit to
receive radio signals is a function of two different features.
The first is the antenna, and second is the electronic
receiver/tuner/amplifier that 'pulls' a signal off the antenna.
1.1 Antenna issues
A 'better' antenna may be
one that is in a better location (especially one that is
outdoors and up higher with better line of sight to the distant
A 'better' antenna may be
one that is more exactly 'tuned' to work best with the frequency
of the signal desired to be received and boosted. This
tuning is achieved by making it an optimum 'electrical' length
to match the wavelength of the signal being received.
Different antenna styles have different ideal electrical
lengths, and the electrical length is not necessarily the same
as the physical length - coils somewhere along the antenna can
vary its apparent electrical length without requiring its
physical length to be the same (but the most efficient antenna
design is with straight wire rather than with coils and other
devices to 'cheat' the system).
Every antenna has an ideal
frequency which it works best at, and a series of multiples of
that frequency where it also works somewhat well, but for all
other frequencies, it is increasingly less optimized. It
is somewhat of an oversimplification to say 'in general, longer
antennas are better than shorter ones' - particularly in cases
where the wave length of the radio signal is very short to start
with (because an antenna never benefits from being longer in
length than the wavelength of the signal it receives).
A CB radio uses frequencies
with wave lengths of around 35 ft, a FRS/GMRS radio uses
frequencies that have about 2' wave lengths, cell phones use
either 12" or 6" radio waves, and Wi-Fi service uses 5" radio
waves. So longer antennas can be a helpful factor with CB
and FRS/GMRS radios, but cell phones and Wi-Fi
repeaters/boosters don't necessarily need a longer antenna.
But there is another - third - factor in antenna design which
might be relevant.
Thirdly, a 'better' antenna
may be one that is directional, so that it picks up signals most
sensitively in the direction that the distant station is
located. On the face of it, directional antennas would
seem only possible with a stationary repeater station, but even
mobile repeaters (eg on vehicles) can have a certain type of
directional enhancement on their antennas - they can be
'focused' so that they receive and transmit not in an even
sphere (or hemisphere) but rather in more of a cylindrical
manner so that the antenna 'listens' primarily straight out from
the antenna, rather than wasting some of its capability by
listening straight up and at other improbable angles - most
signals come from transmitters that tend to be more or less
horizontally distant from the receiver, rather than at sharp
angles up and down.
Directional antennas can
readily double or treble the range at which they send or receive
1.2 Receiver issues
The second aspect of
receiving a signal relates to the electronics which receive and
amplify the signal from the antenna.
A good receiver is very
sensitive - it only needs to detect a very weak signal in order
to be able to do something with it, and needs to have a low
noise amplifier so its own electronic processing of a weak
signal doesn't overwhelm the signal with extra background noise.
A good receiver can also be
very selective, so when it is tuned to a specific frequency, it
only receives that exact frequency and doesn't have any
spill-over signal from nearby frequencies interfering.
Good receivers can have 50%
or more of increased sensitivity compared to not so good
receivers; and can have two or more times less noise and much
2. Retransmitting the
Distant Signal to the Final Receiver
Most of the factors which
apply to receiving a signal now are flipped around and apply
again to retransmitting the signal.
In the case of transmitting,
the issues apply primarily to the amount of power the
transmitter has, although note that, depending on how
directional the antenna is for retransmitting the signal,
amplifier power is not necessarily the most important factor.
It might be necessary to increase the transmitting power by four
or even five times in order to double the range of the signal,
and even the most ridiculously powerful signal will still be
blocked by major obstructions.
As with the receiver,
probably the most important factor is the design and location of
the transmitting antenna.
3. Receiving the reply
from the Final Receiver
Of course, the repeater
station also needs to be able to clearly receive a reply from
the final receiver, and all the same issues apply to this as
applied in point (1) above.
4. Retransmitting the
Final Receiver's reply to the Original Distant Station
And now, the last part of
the 'round trip' of a conversation or data exchange, the
repeater must be able to send the final receiver's response back
to the original distant station, with the same issues as in
point (2) above applying.
Some Special Situations where
Repeaters Can be Used
In addition to the
simple/obvious situation where a repeater can be used to extend
the range and connectivity between two radios, there are some special
situations where perhaps a repeater might not first be thought
of but where they can be helpful.
If you have a line of sight
type radio signal/service, there might be a large obstruction
that prevents the signal/service from getting where it needs to
One example of this would be
an 'urban jungle' - the buildings in a downtown area would block
or interfere with the transmission/reception of a signal from
one side of town to the other, whereas a repeater, located at a
high vantage point - possibly even out of town, might have a
relatively clear unobstructed view of the downtown area.
In this sort of situation,
the total distance traveled by the signal might end up being
much longer, through the repeater, than directly by line of
sight, but you might get very much better quality as a result.
Into buildings or other
Have you ever received a
phone call while driving through a tunnel, or on a metro line?
Normal signals can't penetrate into a tunnel, so there have been
additional cell sites (repeaters) added to give you coverage in
the tunnel or other location.
A similar situation might be
in a building. If you can't get good reception inside your
house or office, maybe you need to have a repeater there, too.
You'd have one antenna on the building's roof - it would be high
up and outside the structure to get best range/reception.
You'd place the other
antenna inside the building, to rebroadcast inside the
house/office the signal received from outside.
The preceding was an example of a
split repeater, where one half of it is in one location and the
other half is in another location.
considered until now have implied that the two parts of the
repeater are in the same location, but there's no reason why the
two parts could not be some distance apart - either a few tens
of feet, or even many hundreds of miles, with a wired connection
running between the two antennas. That type of more
distant connection can often be found with radio and television
stations that are broadcasting into multiple areas.
Multiple Repeaters in a Chain
Sometimes you'll have
repeaters that repeat other repeaters. An example of this
is in a fiber optic cable, where the signal needs to be
amplified, boosted or repeated every few miles along the cable.
An earlier voice cable
across the Atlantic had 22 repeaters, each boosting the signal
1,000,000 times in power. So the sound coming out one end
of the cable had been boosted, in total,
That's a lot of boosting.
Another type of multiple
repeater scenario is where a number of repeaters are all linked
together (probably by land-line). When any one of the
repeaters (or perhaps certain designated repeaters only) receive
an incoming signal to be rebroadcast, they send it to all the
other repeaters and all the repeaters rebroadcast it
This can be used to greatly
increase the effective coverage area of a wireless service.
An interesting specialized
application for a repeater is when it is used to take a radio
signal at one frequency and to then re-broadcast it at a very
Of course all repeated
signals have to be rebroadcast at a slightly different frequency
(otherwise you'd have the repeater end up receiving and
repeating itself in a nasty feedback loop, a bit like you can
get with a public address system sometimes), but typically this
is just a tiny bit different to the original frequency.
But sometimes you might have a repeater that is designed to
patch together two systems with a major difference in
frequencies that might be otherwise incompatible - eg a local
fire department and police department.
In such a case, one
department might operate around the 40 - 45 MHz frequency range
and the other around the 150 - 155 MHz range - a huge difference
that requires very different electronics and antennas in the
radios. And so a repeater would rebroadcast the
frequencies from one system over to the other system and back
again, allowing the two systems to be able to communicate.
Another example is where a
powerful longer range communication system in a car (eg police
car) communicates between the vehicle and a remote base station
(eg at the police headquarters or 911 center) and then a
separate repeater system rebroadcasts the signal at a different
frequency and lower power to a walkie-talkie type radio on the
policeman's belt, so when he is out of the car but not far away,
his low power portable radio can patch through the car's high
power not portable system and keep him in contact with his
application is for a repeater that connects between two
different types of protocol. An example of this would be a
repeater that converts between cellular radio and Wi-fi.
Yet another specialized
application is a repeater that rebroadcasts a secured Wi-fi
signal. You might use this in, for example, a hotel, where
you have to pay for each device you wish to connect to the
So rather than paying three
or four times to connect your laptop, your phone, your iPad, and
who knows what else to the internet, you simply connect your
laptop, either through an ethernet cable or via Wi-fi, and
rebroadcast the signal for your other devices to connect
review of the
excellent and free Connectify software for more information
on how this works.
Can Everything Be
Yes and no. There are
a couple of constraints to the boosting process, especially with
analog signals. Think of each boosting process as being
like taking a photocopy - first of the original, then a copy of
the copy, then a copy of the copy of the copy, and so on.
You lose some quality each time, and any dirt or dust or
imperfections on a copy get passed on to each subsequent copy
The same thing happens with
boosting radio signals. If the received signal is of poor
quality, with static and low clarity, you'll be boosting the
static and distortion right along with the signal.
Sometimes Repeaters Make No
For the sake of
completeness, there can be situations where using a repeater
doesn't improve the communication at all. For example, if
you have two people in two cars, driving along the same block,
but relaying a conversation between themselves through a
repeater station that is on a hill ten miles away, they would
probably find it easier and better to simply transmit directly
to each other rather than going through a repeater.
In addition, if you use a
repeater, you are taking up at least twice as much bandwidth
(something that is always in short supply) as you would if just
communicating directly. When communicating directly, at
the simplest 'simplex' type of communication, you have one
frequency that you use for alternately sending or receiving
communications (eg a pair of walkie-talkies where only one
person can be talking at a time, unlike a phone where both
people can be talking simultaneously).
In contrast, the simplest
repeater system uses two frequencies, and works so that the
originating station transmits on one frequency (F1) and receives
on a second frequency (F2). The repeater receives on F1
and transmits on F2.
And because a repeated
signal covers a larger area, one single person using it is
making the frequency busy for a greater number of other
Repeaters can be either
real-time streaming or 'store and forward' type repeaters.
All voice type repeaters are real-time streaming - they
immediately start re-transmitting the signal they receive, with
only perhaps 50 msec of delay for processing the signal.
Some types of data repeater
are store and forward.
A repeater can extend the
range of a radio signal, and can allow it to reach areas it
would not otherwise reach.
Things to look for in
choosing a repeater would encompass the antenna design, the
receiver sensitivity and noise, and the rebroadcast power of the
Please refer to our series on
real world radio range for CB/MURS/FRS/GMRS radios.
Here is a review of the
software that allows you to use your Windows laptop as a Wi-fi
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22 Sep 2010, last update
31 May 2012
You may freely reproduce or distribute this article for noncommercial purposes as long as you give credit to me
(David Rowell - KF7VVM) as original writer.