Getting the Best Range from your
CB, FRS, GMRS or MURS walkie-talkie
Perhaps the most
surprising discovery - both in theory and in testing - is
that the power of the transmitting radio has very little
impact on its effective range.
A radio that is four
times more powerful than another one may in fact offer no
greater working range!
Part 2 of a 5 part series - click for Parts
FRS radios are advertised as
having a range of 'up to two miles'. I have typically
experienced 0.25 - 0.5 miles. Disappointing, but usable.
And then I read an
advertisement for an 'up to seven miles' GMRS radio. Wow. It had
four times the power of the FRS radio, was newer technology, and
seemed very promising.
Care to guess what its actual
tested range was? Hint : Very much less. But manufacturers can
promote these almost impossible range claims due to the
complexity of what determines the working range of a radio.
Oh - the actual range I get
from these radios? I'll tell you in
Marketing Hype vs Actual
Perhaps conveniently for
sellers of two-way radios, the actual effective range between
two radios can vary enormously depending on many different
A cynic might think this is why radios that give less than one mile of range are
promoted as having ranges ten or twenty times further!
Most of the factors
influencing range are out of our control, but there are several
factors that we can sometimes optimize. Here is a list of the
major issues that relate to effective radio range.
You'll get more range if you
get higher. Even something simple like holding the radio
above your head (and using an extension microphone) can make an
appreciable difference in range.
In some respects, radio
waves are similar to light from a light bulb (indeed, light is
just a higher frequency form of radiation that is otherwise
essentially identical to radio waves).
And so, with this in mind,
here's a quick rule of thumb. If you can see the person you're
trying to communicate with, you are probably within radio range,
no matter which type of radio you're using.
The idea situation would be
if the two of you were on boats on a smooth sea, with nothing
else between you. This would give you the best possible range,
and is probably the type of scenario that manufacturers have in
mind when they make their outrageous claims.
If there are things between
you and the other person, then, depending on the nature of these
obstructions, your ability to send a radio signal between you
will be reduced and perhaps eliminated.
Radio waves do not pass very
well through conductive metal. They don't much like high density
materials (eg concrete) either.
Sometimes all it takes is to
move a few inches to change from a dead spot to a spot where you
have a clear signal. You might notice this with your car radio -
when tuned to a medium-weak signal, and while stopped in a line
of traffic, you'll often notice that just by moving a few feet
you can change from a bad signal to a good signal.
Radio waves don't like
traveling through the ground or water either. This means if you
and your friend are on opposite sides of a mountain, or if one
of you is in a tunnel, you're unlikely to be able to
Note that in some tunnels,
you might have cell phone and even FM/AM radio reception, but
this is because the tunnel has built in 'repeaters' that pipe
the radio signals from outside the tunnel and then rebroadcast
them inside the tunnel.
Biggest Obstruction of All -
People absorb radio waves.
This is the same concept that a microwave oven uses, but whereas
a microwave oven is focusing 1000 watts of energy into one or
two pounds of food, you are only absorbing a small percentage of
one or two watts, and you weigh perhaps 150-200 lbs.
Yes, that does mean that you
are being slowly cooked. But the watts of power per pound of
flesh is very much lower than in a microwave - perhaps 100,000
times less, and so most people believe radio radiation
to be relatively harmless. However, increasingly convincing
studies are suggesting that even low powered radios and cell
phones, if used for long periods of time and held close to you,
may cause cancers or other problems.
Which means there are two
reasons to avoid absorbing any more radio waves than you have
to. The first reason is for your health!
The second reason is
because, obviously, the more radio power you absorb, the less
that can be transmitted or received - the shorter the range your
radio will have.
Two simple things will
minimize the power you are absorbing. First, don't hold the
radio anywhere near its antenna. Secondly, don't have the radio
clipped to your belt - instead, hold it away from you (consider
using an extension microphone for best results). These two
things can make a big difference - in the worst case scenario,
you might be inadvertently absorbing as much as 80% of the radio
energy being radiated; in a best case scenario, you'll perhaps
be absorbing 10%-20%.
Another Big Obstruction - Your
If you are using a radio
inside a car, then the metal frame of the car shields a lot of
the radio signals from getting in from outside, and shields even
more of the signals you transmit from inside getting out again.
To get the best range in a
car, hold your radio with the antenna as close to a window as
possible so that it can 'see' out in as broad an area as
In theory, like a beam of
light, radio waves travel in a straight line. But, in practice,
lower frequency radio waves (like AM radio) actually curve
around the surface of the earth, which is why AM radio signals
can travel very much further than line of sight. CB radio
signals are almost too high a frequency to curve, but they do
have a little bit of curvature present. Other (higher frequency)
radio signals go in straight lines only.
There is another interesting
exception to the 'beam of light' principle. Some radio waves
reflect off the atmosphere and then 'bounce' back down to the
earth. The extent of the bounce can vary depending on the time
of day and the level of solar activity from the sun.
CB frequencies usually just
go through the atmosphere, but occasionally they will bounce
back. The strange result of this is that you might find that a
person 30 miles away is out of range (beyond regular range), but
a person 100 (or even 1000+) miles away is clearly in range, due
to a signal bouncing up and back down again.
This 'DX' or 'skip' feature
of CB radios is usually a nuisance rather than a help, because
all of a sudden, your channel might become crowded with unwanted
extra signals from hundreds or thousands of miles away, making
it difficult to communicate with your friends on the next block.
If there are other people
transmitting on the same frequency, or sometimes on an adjacent
frequency, then the worst case scenario is that you can't use
that frequency at all - their signal blocks out your signal.
When two people transmit on
the same AM frequency, the two signals interfere with each other
and usually all you hear is a high pitched squeal.
When two people transmit on
the same FM frequency, the stronger signal typically completely
obliterates the weaker signal.
It makes no difference who
started transmitting first. The laws of radio physics basically
say that two people can't use the same frequency at the same
time. Any time that you see what seems to be two people using
the same frequency at the same time (for example on a cell phone
when you can talk and listen simultaneously) what is happening
is that the cell phone is actually using two different
frequencies - a send frequency and a receive frequency. And the
person next to you - also using a cell phone - he is using
another two more frequencies.
Sometimes a person is
transmitting a very powerful signal on one frequency that is so
strong that it overwhelms your receiver, and some of its
transmission frequency 'spills over' into your receiving
frequency as well. This can be a problem with poorly tuned
equipment (or too powerful), and the only thing you can do is try and move to
another frequency further away from the interfering channel.
In addition to this obvious
interference, weak interference - from other people transmitting
a long way away - can also interfere with the clarity of your
signal, particularly as the range between your own radios
If you're hearing background
interference becoming stronger on the channel you are using,
simply switch to a different channel that might be less busy.
The chances are that your
radio has an automatic squelch function. This is not as good as
a manual squelch.
Squelch cuts out the
background noise that you would otherwise hear when there is
no-one transmitting on the radio. If you tune your AM radio to a
space between stations, you'll hear some 'static' or background
noise. A squelch control tells the radio 'ignore anything that
is just a weak background noise or meaningless static and don't
play those sounds through the speaker at all'.
This is great when it
correctly guesses what is unwanted meaningless static (to
ignore) and what is an important but very weak radio broadcast
(to play through the speaker). With a manual squelch control,
you can carefully balance this setting, but with an automatic
one, you will find that it is causing you to miss weak
Manual squelch controls
require more work on your part, but, if adjusted correctly, will
give you more range than an automatic squelch control.
Not all receivers are
equally sensitive to weak signals. The more sensitive a receiver
is, the better a job it will do of pulling in the weak signals
and making sense of them, presenting them to you as something
you can clearly hear and understand.
Choosing a radio with
excellent receiver sensitivity (and selectivity) is more
important than choosing one with high transmission power.
You'll get longer battery life with a lower powered but more
highly sensitive radio, and usually get better range, too.
This is illustrated dramatically in
part four of this series.
Receiver sensitivity is
usually measured, in a radio's specifications, in terms of
microvolts for so many dB of either signal/noise ratio (CB and
AM radios) or SINAD (FM radios such as MURS, FRS and GMRS). The
lower the number, the better.
Note that some radios don't
disclose their receiver sensitivity. It is a safe bet, in such
cases, that the receiver is not a very good one!
For a CB radio, you would
expect to see sensitivities no greater than 1.5 uV for 10dB of
S/N. A good receiver would have a sensitivity of less than 1.0
uV and a great receiver would have a sensitivity of less than
For MURS, FRS and GMRS, you
would expect to see sensitivities no greater than 0.5 uV for 12
dB SINAD. A good receiver would have a sensitivity of less than
0.3 uV and a great receiver would have a sensitivity of 0.2 uV.
The answer to this issue
surprises many people. For CB radios, more power usually gives you an
appreciable impact in terms of more range. But, for the higher
frequency radios, an increase in power has little or no impact
The reason for this is two
fold. Firstly, the maximum range of these radios is 'line of
sight'. To achieve this range, the radios do not need very much
power. More power will never get the radios to transmit further
than 'line of sight' and if moderate power (0.5 - 1 Watt) is
enough to achieve the maximum line of site range, any more power
The second reason is that,
depending on the type of antenna you are using, range is
proportional to somewhere between the square root and the cube
root of the power. In other words, if you double your
transmitting power, the best case scenario is that your range
will only increase 40%, and the worst case scenario is that it
will increase less than 25%. Increase power ten fold, and range
may not even double.
The third reason is that
many of the factors preventing radios from achieving their
maximum 'line of site' range are so major that even a ten fold
or twenty fold increase in the radio's transmitting power might
not have much impact. If much or all of the transmitting power
is being soaked up by a building or a hill (or by you!) then
increasing power will not solve that problem, it will merely
feed even more power into the building or hill or person.
In our testing (described
in parts three and four) we found that the design and quality of the unit was
more important than its power. You'll get better results with a
high quality low power unit than you will with a low quality
high power unit. And your batteries will last longer, too!
We did testing using two
identical dual power units (Motorola G223 GMRS radios) and compared their
range when using low power (0.5 watt) and high power (2 watts).
There was almost no difference in range whatsoever - perhaps the
higher power would sometimes provide an extra 1/10th of a mile
in range. Interestingly, these radios were regularly
out-performed by a low power 0.5 watt pair of FRS radios, which
confirms that receiver sensitivity and overall design are more
important than power by themselves!
Batteries and Voltage
The power that the unit is
capable of transmitting is a function of the square of the
battery voltage. Voltage is very important. If you are choosing
between regular alkaline batteries (at 1.5 volts each) and
Ni-Cad or NiMH batteries (at 1.2 volts each) you will get a 56%
increase in transmitted power with the alkaline batteries.
Sure, more power doesn't
always mean more range, but that is no reason to accept any less
than the most power your unit is capable of generating. Keep
your batteries fresh and fully charged.
The FCC limit a FRS radio to
only using its fixed small antenna built into the radio unit.
But the other three types of units are allowed to have external
Some models of GMRS and MURS
radios are designed for external antennas, while others do not.
Almost all CB radios are designed to allow for an external
You will get noticeably
better results and more range with an external antenna. Indeed,
you'll usually find that the single most important thing you can
do to improve your effective range for both transmitting and
receiving signals is to get a properly designed and properly
tuned antenna for your radio, and to locate it in the best
Of course if you're using a
radio as a portable unit while walking around, there isn't much
you can do about getting a better antenna, although sometimes
you can substitute the standard short (eg 3") antenna for a
longer (eg 6") antenna and that might give you some effective
The best opportunities for
an external antenna are if you are using the radio in a car or
in a fixed location (home or office). You can then locate an
antenna outside of the car (remember that the car shell stops a
lot of the radio waves from traveling in or out of the car) or
house/office (radio waves don't much like concrete, either!).
An antenna can also be
mounted higher up, so as to be clear of more obstacles and to
have better line-of-site to the other unit you are communicating
There are three more
benefits of an external antenna. First of all, it can sometimes
give you a 'ground' as well as an antenna (half of your radio
signal needs to go to a 'ground' - if you don't have one, then
that half is being effectively wasted).
Secondly, the external
antenna can be made the exact length to work best with the
frequency of your radio. Every radio frequency has a matching
wavelength size, and an antenna needs to be an exact percentage
of this size for maximum efficiency (usually about half the wave
length is ideal).
Thirdly, an external antenna
can be designed to concentrate the radio signal in certain
directions. Instead of allowing the signal to radiate in every
direction equally like a sphere, a good antenna will typically
make it radiate out in a flat circle. There is no need to send
signals straight up or straight down - the people you are
wanting to talk to are usually at the same level as you, just at
a distance away. By directing the signal only into the
horizontal, none of the signal is wasted, and you end up getting
as much as double the range as you would with a plain undirected
If you are planning on using
radios in cars, then you should get an external antenna. An
external antenna for a GMRS radio is a very small short thing -
it can be as little as six inches in height, and will probably have a magnetic
mount to simply stick to the roof of your car. Its wire can
be fed through the rubber around the car door jamb.
A CB radio antenna is much
larger - perhaps as much as 3 ft in length or more.
If you do get an external
antenna, you should use a SWR meter to complete the fine tuning
of the antenna, to ensure that it is best balanced and matched
to your transmitter. Most antennas are 'tunable' (usually by
slightly varying their length) and the difference between a
properly tuned and a badly tuned aerial can be as much as 50% in
terms of effective power lost.
Summary - How to Get the Best
More power is good, but not
the most important thing.
The biggest impact on range
will be the actual design of the radio - its receiver
sensitivity in particular, and how viciously its squelch cuts
out weak signals. Get a unit with manual squelch, if possible,
and with a very low number for its receiver sensitivity.
The other most important impact has
to do with your antenna. If it is possible to have an external
antenna (FRS radios are not allowed external antennas, the other
three types are) then this will make a positive difference. If
you are stuck with the built in antenna, try and hold the radio
as far away from you as possible (ie up in the air above your
head - use an external microphone) and, if in a vehicle or
building, as close to a window as possible where it can 'see' in
the direction of the person you're hoping to communicate with.
Rechargeable batteries are
wonderfully convenient, but if your radio is designed for using
the same number of either
regular alkaline or rechargeable batteries, you'll get more
range from the higher voltage alkaline batteries.
See also Parts 1, 3 4 & 5
Part 1 we explain the different types of personal radio
services available to you, and what they variously mean.
Part 3 we give you real world test results and help you
choose which is the best system for your needs.
Part 4 we
repeat the testing, this time using 'professional grade' radios
to determine just how much more performance you get from these
much more expensive radios.
Part 5 we
explain the confusing mismatch of channel number allocations to
different FRS/GMRS radios.
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18 July 2003, last update
19 Dec 2013
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.