Personal Radio Communication
Services |
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These two walkie-talkie type radio handsets offer 22
combined GMRS and FRS channels and list for only $39.99.
Others can be found for even less.
Handheld two way
radios are today an incredible bargain, but only if they
work as you expect and need them too.
Part 1 of a 5 part series - click for Parts
One Two
Three
Four
Five |
CB radios experienced a sudden
burst of fame - or infamy - during the late 1970s, with the song
'Convoy' and a string of movies such as 'Smokey and the Bandit'.
Today, CB radio service is
largely defunct (other than for truckers), but new types of
radio services - notably FRS - provide similar or better service
for individuals and families wanting a convenient way to keep in
contact over relatively short distances.
In this first part of a new
series on personal radio services, we explain the different
types of radio service available to you. In the second part we
discuss the theory of what determines the effective range of
these radios. In the third part we test out CB, FRS and GMRS
radios and tell you which services give the best range and
convenience.
Typical Uses for these types of
radios
All these different types of
radio services are intended to be used for short range
communications - typically of no more than a mile or two. If you
are with other family members at a Shopping Mall, or at some
type of Outdoors Event, in theory these radios will enable you
to all keep in touch with each other.
The radios can also be
helpful if you are traveling with friends in two (or more) cars.
You can easily keep in contact if you get separated (as long as
not too much distance gets between you), and discuss where
you'll stop and plan for turns and get in the correct lane in
plenty of time.
These radio services are
unlimited and free (except for the need to buy an annual license
for GMRS) and work anywhere without the need to use cellphone
type external transmitting towers or other equipment. This can
make it very convenient whenever you want quick easy short range
communications.
With the possible exception
of CB, none of these services work over anything other than very
short range. CB sometimes reaches out as far as 10-15 miles (and
in special circumstances, can travel hundreds of miles).
What the Acronyms Mean
The four types of radio
service we're looking at are :
CB |
-
Citizens Band radio.
-
This is an AM service with 40
channels that operates at approximately 27 MHz.
-
Maximum power of 4 Watts. Can
have separate antenna (for better signal).
-
If operating in SSB mode can have 12 Watts of PEP (= slightly better
range).
-
Few handheld radios manufactured now
- mainly sets for in-car or at-home use. Handheld sets have
large aerials.
-
Can be used for
business or personal use. No license required.
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FRS |
-
Family Radio Service.
-
This is a low power FM service with
14 channels that operates at approximately 462.5 MHz and 467.5 MHz
(channel frequencies are in the mid-points between the GMRS
frequencies).
-
Maximum power of 0.5 Watts. No
separate antenna.
-
Cheapest type of radios. Only
handheld sets made.
-
Can be used for
business or personal use. No license required.
|
GMRS |
-
General Mobile Radio Service.
-
This is a higher powered FM service
with 8 duplex or 16 simplex channels (in theory, but usually only
the 8 lower frequency bands are used, the upper 8 are used to
transmit to repeaters) that operates at similar frequencies to FRS
(around 462.5MHZ plus a matched duplex channel around 467.5MHz).
-
Maximum power of 50 Watts. Can
have separate antenna.
-
Also can operate on seven of the frequencies (the 462.5MZ set) used
by FRS, with maximum power of 5 Watts (but FRS radios on the same
frequencies are limited to 0.5 Watts).
-
Advanced sets can be used with
relay/repeater stations to give greatly increased range.
-
For personal use
only, not for business use. FCC license required.
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MURS |
-
Multi-Use Radio Service.
-
This is the newest of the four
services, and is an FM service with five channels operating at
approximately 153 MHz.
-
Maximum power of 2 Watts. Can
have separate antenna.
-
Most expensive type of radios
(currently) but will probably come down in price as becomes more
popular.
-
For business and
personal use. No license required.
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Frequencies
It is interesting to compare
the frequencies of different types of other radio services so as
to see where the above set of frequencies are in relation to
other types of radio service.
(Note that 1 MHz means 1
megahertz and is one million cycles per second, and 1 GHz means
1 gigahertz and is one billion cycles per second.)
Human hearing |
20 Hz - 20kHz (0.00002 - 0.02 MHz) |
AM |
AM radio stations broadcast between 0.5
and 1.5 MHz. |
Shortwave radio |
Most long distance shortwave radio is
in the 2.3 - 30 MHz range, and broadcast in AM |
FM |
FM radio stations
broadcast between 88 and 108 MHz. |
Weather
Service |
The seven
weather service radio channels broadcast around 162 MHz. |
TV |
Channels 2-6 operate
between 55 - 88 MHz.
Channels 7-13 operate between 175 - 215 MHz.
Channels 14 - 83 operate between 471 - 890 MHz.
|
Cordless Phones |
Most cordless phones these days work on
either 900 MHz or 2.4 GHz (= 2400 MHz). Older phones work on
lower frequencies. New phones are now being
released that work on 5.8 GHz |
GPS Navigation Service |
GPS satellites broadcast a signal on
two frequencies, 1575.42 MHz (L1) and 1227.6 MHz (L2). |
Cell Phone |
Cell phone services
operate between 800 - 900 MHz and between 1800 - 1900 MHz.
New '3G' cell phones work around the 2200 MHz frequency.
|
Satellite phone service |
Satellite phone
service uses L band frequencies around 1.62 GHz. |
Satellite radio - XM Radio and
Sirius |
Satellite radio uses a narrow band of
frequencies around 2.3GHz, which is part of the 'S band'. |
Wi-Fi
Bluetooth
Microwave ovens |
2.4 GHz (= 2400 MHz).
Also used by some cordless phones. |
Satellite tv |
C band satellites - using the older big
dishes, use 3-7 - 4.2 GHz.
Ku band satellite systems - the new digital systems with small fixed
dishes - use 10.7 - 12.5 GHz. |
Police Radar Guns |
Police radar guns operate in three
frequency bands :
X band is
the oldest, and is about 10.5 GHz. It is also used by many other
devices such as motion detectors for automatic doors and burglar
alarms.
K band is 24 - 24.25 GHz and is the most common band in use.
Ka band is the newest frequency band and is less commonly found.
It ranges from 33.4 - 36 GHz. |
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Public and Not so Public Radio
Services
In simple terms, there are
four main types of radio services that people use :
- Services that require
the operator to pass an exam (eg ham radio licenses)
- Services restricted to
business users only
- Services open to the
general public (and which may or may not also allow business
use) for which an annual license needs to be purchased (but
no exams need be passed - all you do is fill out a form and
pay a fee)
- Services open to the
general public (and which may or may not also allow business
use) for which no licensing is required and for which no
annual fee needs to be paid
For the purpose of these
articles, we will ignore the first two categories. Thee four
services we are reviewing are either type 3 (GMRS) or type 4
(the other three).
If you have other needs -
for example, if you have a boat or plane, then other types of
radio communications may be better for you (and sometimes might
be mandatory).
Because these four types of
radio service are public, anyone with a radio tuned to the same
channel can listen in on what you are saying.
A worse feature is that you have to share that channel with
other users, too. Sometimes, and in some places, some channels
will be very busy with lots of people using the channel (and
often for incredibly stupid things, or so it seems to other
people impatiently waiting to use the same channel) and it can
be almost impossible for you to use it yourself.
It is also a nuisance when
you're trying to carefully listen out for a radio transmission
from a friend, and instead you're all the time hearing other
broadcasts from other people.
For this reason, it is good
to have an agreed arrangement so that if the channel you
normally use is busy with other users, you have a planned
alternate channel you know to go and use instead. Some radios
also let you monitor two channels simultaneously, making it
easier to catch calls from your friends, whichever channel they
are using.
Privacy Codes
A partial solution to the
annoyance of lots of other people talking on the same channel is
the use of so-called privacy codes - known as CTCSS or DCS
(Continuous Tone Coded Squelch System or Digital Coded Squelch,
if you must know!). This enables you to tell your receiver only
to listen to particular transmissions, and to ignore all others.
There are 38 different CTCSS codes and 83 different DCS codes
available for each radio channel, making it easy for you to
assign a code to the people you want to talk with that probably
no-one else will be using at the same time.
Although these codes are
sometimes referred to as 'privacy' codes, they are NOT privacy
codes. They don't stop anyone else from listening in on your
conversation. They only stop you from listening in on other
people's conversations! If someone else is on the same channel,
but without activating their CTCSS/DCS feature, they can still
hear everyone's conversations, no matter what type of coding
they are using.
There is also a potential
problem with these codes - you might not realize that someone
else is using the channel before trying to use the channel
yourself.
What Happens if Two People
Transmit at the Same Time
If two people transmit at
the same time on an AM (CB) radio frequency, people listening to
the channel will probably hear neither person. Instead, they'll
just hear a high pitched squeal caused by the two radio signals
interfering with each other.
If two people transmit
simultaneously on an FM (FRS GMRS MURS) radio, then usually the
stronger of the two signals will block the weaker signal. You'll
only hear the stronger signal, the quieter signal will be
rejected entirely.
Simplex or Duplex
Two way radios are either
simplex or duplex. A simplex service is one where you send and
receive (ie listen and talk) on the same frequency. A duplex
service is where you send (talk) on one frequency but receive
(listen) on a different frequency.
A duplex service has two
capabilities that a simplex service does not. Firstly, a duplex
service can be used so that you can simultaneously talk and
listen at the same time - just like on a telephone or cell
phone, which are duplex services.
Secondly, a duplex service
can be used with a repeater station. A repeater station is
usually situated somewhere with good coverage, and has an
excellent aerial system, sensitive receiver and high power
transmitter. It rebroadcasts signals that it receives, but on a
different frequency. The repeater gives much longer range
coverage.
All four radio services are
'simplex' systems, although GMRS can also be operated in duplex
mode (if you have a duplex capable radio set and access to a
repeater).
There are also some
inexpensive (about $20) very short range (about 100 yds) duplex
CB radio systems (basically they are two walkie-talkies
connected together so that one is transmitting on one channel,
and the second is listening on a different channel, and vice
versa on the other pair).
PTT or VOX
Most radios are PTT - Push
to Talk. In order to transmit, you have to push a button, and
then, when you have finished speaking, you release the button.
Some radios also have a VOX
feature. This is a Voice Operated Transmitter - the microphone
is listening and any time it hears sounds, it automatically
switched the radio to transmit.
A VOX feature seems to be
really clever and convenient, and sometimes there are situations
where you have both hands busy, but need to be able to use the
radio too. But, in practice, most of the time, these features do
not work well.
They either do not detect
your voice when you start to talk, or else, many other random
sounds also trigger the VOX circuit, with the result being that
your radio is transmitting unnecessary rubbish a lot of the
time, annoying other users of the channel, and using up your
batteries faster than necessary.
We recommend you do not use
the VOX feature on radios unless you're in a special situation
where it is essential.
Accessories
A useful accessory can be a
combination earpiece/microphone.
If you're using rechargeable
batteries (sometimes a good idea, but sometimes also a bad idea
- see part 2) then you'll want some sort of battery recharging
unit as well.
Using Special Words and Phrases
on the Radio
You don't need to start
using special 'CB-slang' when using these radios. The idea of
all these radio services (even, in theory, including CB, too!)
is that you use them only to talk to people that you already
know, and all you need do is speak normally, the same as when
chatting in person.
If you have GMRS radios, you
need to give your official call sign every 15 minutes or so, but
with the other radios, you don't need any special identifiers or
anything. Just talk any way you want to.
Read more in Parts 2, 3 4 &
5
In
Part 2 we discuss how it is that manufacturers can claim
ranges of 'up to seven miles' when the effective range - as
tested by us - is sometimes as little as one twentieth the
claimed range. Many factors influence maximum range - some we
can influence, most we can not. In particular, read the
startling truth about the importance of transmitter power to
give you more range.
In
Part 3 we report on real world test results of 'consumer
grade' radios and help you
choose which is the best system for your needs.
In
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.
In
Part 5 we
explain the confusing mismatch of channel number allocations to
different FRS/GMRS radios.
Related Articles, etc
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Originally published
27 June 2003, last update
20 Jul 2020
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.
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