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CB
radio is intended to provide short-range radio communication for almost any
purpose, business or personal. Equipment is inexpensive and there are no
license fees to pay. There are two types of CB equipment: HF 27 MHz and
UHF 477 MHz.
The
'megahertz' (MHz) refers to the radio frequency on which the equipment
operates. 27 MHz is between the 530 -
1602 kHz AM and 88 – 108 MHz broadcast bands.
477 MHz is between the VHF (eg 2, 7, 9 & 10) and UHF (eg SBS 28) TV
channels. Signals on different
frequencies behave differently, and thus affect the performance of
equipment.
The
differences between 27 MHz and UHF are explained below. Information is also provided on deciding
between the two and the limitations of CB communication.
27MHz AM/SSB (aka 'CB')
History
27 MHz
CB started in the United States in the 1950s and spread worldwide in the
1970s. Australia legalised CB in the
late 1970s, following a vigorous campaign by truck drivers and others who
wanted cheap, local communications for personal or business purposes. The government initially allocated 18
channels for CB. Operators had to
obtain a government call sign, pay an annual licence fee and use type-approved
equipment. However unlike amateur radio, no
technical examination was required.
In
Australia 27 MHz CB was planned as a temporary allocation, with users to move
to UHF in five years. However it proved so popular that the band was extended
to its current 40 channels in 1982. If
you hear an inexperienced person talk about 'CB' the chances are that they are
referring to 27 MHz.
Most CB
operators did not bother with licensing.
Provided you did not cause interference, used illegal amplifiers or make
a nuisance of yourself, the chance of being caught by Department of
Communications inspectors was slim. The
cost of policing was probably higher than revenue foregone. This was recognised in 1994, when the
government abolished CB licence fees.
However operators must still use their equipment in accordance with the
CB class licence, a copy of which is available on the Australian Communications and Media Authority website.
Though usage of 27 MHz CB has fallen dramatically in the last decade, it remains the cheapest method of
basic local communications, especially in hilly areas. 27 MHz activity peaked in the 1970s, remained fairly popular
in the 1980s, and declined in the 1990s as most users moved to UHF CB, amateur radio, mobile phones, IRC internet chat
or simply gave it away.
Capabilities
27 MHz is
capable of both local and interstate communication. However the latter
cannot be relied upon. What 27 MHz can do depends on the
transmission mode (AM or SSB), with SSB providing better results when
signals
are weak and/or over long distances.
Locally,
expect communication distances of between 5 and 15 kilometres on AM. Actual range achieved will depend on antenna
efficiency, terrain and interference levels.
Well-equipped home stations will do better than a mobile station. On SSB, distances of between 15 and 30
kilometres are common, with 3000 km sometimes possible under favourable
conditions. Good conditions are often
called 'skip', so-called because the signal bounces ('skips') off the
ionosphere on its way to the other station. Long-distance
propagation is most common in December/January each year and throughout the
year during times of high sunspot activity.
In the last decade or so 27 MHz AM activity has declined enormously. These days, you'll have
no problem finding a vacant channel; even in major cities it is common to flick through them all
and hear nothing. Major retailers have stopped selling 27 MHz radios, so you will need to find one of the
few specialised communications shops, haunt the pawn shops or peruse the local
classifieds to find equipment for sale. Nevertheless AM remains suitable for
groups desiring cheap car-to-car communications amongst themselves. If your interest
is more recreational, you'll do much better if you get a set with SSB (ie LSB and USB settings) as
well as AM. SSB maintains a significant 'hobby' following, with many operators erecting large
beam antennas to allow interstate communications. CB is a public medium so be prepared to hear all types on the
air!
477MHz UHF FM (aka 'UHF')
History
Like 27
MHz, UHF CB also started in the 1970s.
However unlike 27 MHz, UHF CB is unique to Australia. The 40 UHF channels were set up as an
alternative to 27 MHz when government policy was that access to 27 MHz would
only be temporary. Early UHF sets were
expensive and not always reliable. The
line-of-sight characteristics of UHF made it poor in hilly areas. As a result, UHF CB grew slowly for the
first few years of its life.
Farmers
were the first group to adopt UHF CB from the early 1980s. Farmers were soon joined by truck drivers
and rural businesses wishing to take advantage of UHF's crisp, clear
signals. UHF is also popular amongst
travellers on major highways throughout Australia, as it provides a useful
means of calling for help or passing on road or weather warnings. In
the cities UHF activity is a mixture of general chit-chat and business
communications.
The
main reason for UHF's growth was the spread of repeater stations and improved
(and cheaper) equipment. UHF CB has
been so successful that it is now more active than 27 MHz in most places.
Capability
UHF CB
uses the FM transmission mode. UHF gives clear, crisp local communication
without the long-distance interference sometimes heard on 27 MHz. UHF is
also less susceptible to power line noise than 27 MHz. Its main disadvantage is that it performs
poorly in hilly and forested areas due to its 'line of sight'
characteristics. Typical direct
(simplex) car-to-car ranges of UHF vary between about 5 kilometres in urban
areas to 20 kilometres or more in open countryside. However if located on a hilltop, distances of 50 kilometres are
common, even with low-powered handheld equipment.
UHF
really comes into its own when repeater stations are used. Repeaters are installed on hilltops and
retransmit signals received on one channel onto another channel. They are
set up by community groups or commercial organisations but can freely be used
by everyone. Distances of 50 to 100 kilometres are commonly achieved via
repeaters, even if mobile or handheld transceivers are used. Most urban and rural areas are served by at
least one repeater. To listen for the
repeaters in your area, search for signals between channels 1 and 8. Those channels are busy most of the time are
likely to be repeaters.
CB Radio History
