All material on this site (c) Peter Parker VK3YE
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 FM broadcast bands. 477 MHz is between the VHF and UHF 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.
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. A basic 40 channel 27 MHz AM only set is pictured below. 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, 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 since the 1990s as most users moved to UHF CB, amateur radio, mobile phones, IRC internet chat or simply gave it away.
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.
27 MHz AM activity has declined enormously in the last 20 years. 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. The biggest challenge may be finding new equipment to buy, though second hand CB sets are cheaply available from amateur radio junk sales. 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!
All currently-available 27 MHz CB radios operate on the following standard 40 channels:
1 26.965 21 27.215
2 26.975 22 27.225
3 26.985 23 27.245
4 27.005 24 27.235
5 27.015 25 27.255
6 27.025 26 27.265
7 27.035 27 27.275
8 27.055 28 27.285
9 27.065 29 27.295
10 27.075 30 27.305
11 27.085 31 27.315
12 27.105 32 27.325
13 27.115 33 27.335
14 27.125 34 27.345
15 27.135 35 27.355
16 27.155 36 27.365
17 27.165 37 27.375
18 27.175 38 27.385
19 27.185 39 27.395
20 27.205 40 27.405
Notes on channel allocations:
1.Several channels are set aside for special uses.These are:
Channel 8 Road Channel (AM)
Channel 9 Emergency Channel (AM)
Channel 11 Call Channel(AM)
Channel 16 Call Channel(SSB)
Channel 35 Unofficial Call Channel (SSB)
2.Most AM activity is between channels 1 and 15, and most SSB is between 16 and 40. Most SSB operators use lower sideband (LSB).
3. Channels are mostly spaced at 10 kHz intervals, except some lower channels, which are 20 kHz apart. This is to make room for non-CB uses on 26.995, 27.045, 27.095, 27.145 & 27.195 MHz. These frequencies are used for low-power walkie-talkies, baby monitors, garage door openers and remote control toys.
4. Channel 8, the 'road channel' is commonly used by truck drivers. Never operate on Channel 9 except to call for help or respond to a distress call. Channels 11 and 16 are call channels on which you establish initial contact and then move to another channel.
5. 27.240 MHz was allocated to handphones (walkie talkies) prior to the legalisation of CB radio in the 1970s.
6. Many crystal-controlled handheld CBs (available up to the 1980s) were supplied with crystals for Channel 14.
7. Early CB transceivers had 18 or 23 channels. 18 channels was the first Australian system while the Americans used 23 channels. Australia eventually adopted the expanded American 40 channel system which included all the previous 23 channels. Channel numbers on the 18 and 23/40 systems are different, though an 18 channel set will still communicate with a 23 or 40 channel radio on most lower channels.
With the trend to UHF, these days it can be hard to find 27 MHz equipment in the electronic stores. That which is still available are usually mobile transceivers for in-car mounting. However mobile transceivers can also be used at home with a power supply and base station antenna.
Base station and handheld transceivers also used to be available.Base radios were poor value as they were often just a mobile radio in a bigger case with inbuilt power supply.Due to their price tag they disappeared from the market. 27 MHz handhelds became obsolete when UHF handhelds became cheap and, with the help of repeaters, could achieve quite long distance communication without unwieldy telescopic antennas.
Early CB radios used electronic components called crystals to set their operating channel.Because crystals were expensive (and two were needed for each channel), early transceivers only operated on a few channels. However, by the time CB was legalised, vehicle-mounted radios were using banks of crystals and elaborate frequency mixing techniques to cover the full 18 or 23 channel band. This was still expensive, so phase-locked loop (PLL) frequency synthesisers were soon developed to allow many channels to be generated from a single crystal. Apart from the cheaper handheld transceivers, almost every CB radio made since 1980 uses a PLL synthesiser.
The main choice for the buyer is whether to spend more for an AM/SSB set or buy a set that does AM only.SSB, or single sideband, is better for longer distances, and/or when signals are weak. SSB also cuts through interference better. The more serious hobby user operates on SSB for these reasons. On the other hand, if your only use for CB is for car-to-car communications up to about 5 kilometres, an AM-only set is all you need.
27 MHz CB transceivers normally have the following controls:
Channel select: allows you to switch between channels 1-40.This may either be a rotary knob or up/down buttons.
On/off/volume: same function as on a transistor radio
Squelch or mute: Adjust at point where noise stops.This allows silent monitoring of channel. If someone talks the squelch is 'broken' and you will hear their voice. Disable the mute (by adjusting for hiss) if signals are weak.
ANL: Automatic Noise Limiter. Reduces noise from receiver when monitoring. Few of these switches actually did much good and those that appeared to work sometimes just muffled out the high tones.
PA: Public Address switch.With the addition of an external speaker you can use the CB as a PA system.
RF Gain: Reduces the receive sensitivity.Handy to avoid overload from nearby CBers.
AM/LSB/USB: Selects between AM and SSB sideband (AM/SSB sets only). A sure-fire way to tell if the set you're thinking of buying has SSB or not.
Clarifier: Allows SSB signals to be tuned in better (AM/SSB sets only)
If your radio has a duplex switch, it is not a 27 MHz radio, but a UHF transceiver instead. Keep reading!
The general rule is the longer and higher the antenna, the better.
Mobile antennas are normally mounted on the roo bar, bonnet or in the centre of the roof.A roof-mounted antenna is better as it is higher and provides good reception in all directions. However tall roof-mounted antennas can snap if driven into a low garage or low overhanging trees. If a roof-mounted antenna is not possible, the next best choice is one mounted on the roo bar. As it is not mounted central relative to the car body (antenna groundplane) it will do better in some directions than other. Nevertheless it will still work well, with thousands being in use every day.
An antenna length of 1.5 metres or better is recommended unless you need only very short-range communication or have limited clearance. You can buy base-mounted springs to make the antenna more rugged, but this will necessitate re-tuning the antenna for optimum performance. Retuning is easy if the antenna has an adjustable sliding top section, otherwise a few centimetres will need to be sawn off the top to compensate for adding the spring to the base.
Base station operators have a variety of antenna choices.
The cheapest antenna consists of a mobile antenna mounted on a metal roof, which acts as a groundplane.A common mistake made by beginners is to omit the ground plane, by simply mounting the whip on a pole. This will provide poor reception, will reduce transmitting range and cause a mismatch so that the radio cannot deliver its full transmit power. If the antenna is to be mounted on a pole, a groundplane can be fashioned from three or four 2.65 metre lengths of wire connected to the shield of the coaxial feedline at the antenna. These wires should extend approximately 45 degrees to the horizontal.Nylon fishing line or thin rope can be attached to plastic insulators to hold the groundplane wires in position. A groundplane made from a mobile whip will be a compromise, but will provide good short-distance communications.
For the operator wishing better performance, half-wavelength verticals are available. The most famous one was the legendary 'Stationmaster'. These are approximately 5.5 metres long. Unlike short mobile whips they are ground-independent and can be mounted on a pole.If mounted in the clear at roof height, a Stationmaster will provide good local and interstate communication in all directions. The performance possible and the absence of a groundplane make half-wave verticals excellent choices for the beginner.
More serious CB operators use a directional beam antenna. Beams look like giant TV antennas. They can be rotated to provide strong signals into a particular area and reject interference from other directions. If interstate signals are weak on a vertical, switching to a beam will often improve reception and allow communication. Because their elements are horizontal and most other antennas are vertical, beams are a poor choice for local communications.Their directionality is also a liability when speaking to several others in a group. This is why experienced operators have both a vertical and a beam and use an antenna switch to select between the two. Beams are good for the operator interested in long-distance communication.For others a vertical is probably a better choice.
Antennas are connected to the transceiver via special coaxial cable. The cable is similar to that used for TV antennas, but is rated at 50 ohm rather than 75 ohm. The type known as 'RG58' is adequate for mobile and base station installations. However if using long cable lengths (10 metres or more) in a base installation, the use of the thicker 'RG213' is suggested to reduce losses.
The following accessories are in common use and can enhance the efficiency of your 27 MHz CB station. To find most of them you'll need to either find a specialist communications shop, hunt around at hamfests, swapmeets or second hand shops or even make your own.
Power supply: A power supply is required if you wish to use your CB from home.It needs to provide aregulated voltage around 13.8 volts.It should have a capacity of 2 or 3 amps (continuous) minimum.Those who use supplies that are too small or are poorly regulated (eg a car battery charger) will find that their signal sounds distorted on air, with hum prevalent. A good tell-tale sign of this is the dial lights on your radio – if these dim significantly when you're talking, it means your power supply isn't up to the task. Some more technically inclined operators have successfully modified computer power supplies to use with CB equipment; if you can do it it's a dirt cheap way of powering your rig, provided you don't electrocute yourself first!
External speaker: Particularly helpful in noisy vehicles, or if you want better sound when using equipment at home. The connection is almost always a 3.5mm mono plug.
Noise-cancelling microphone: Again helpful if operating in a noisy environment. Reduces extraneous noise on your transmitted signal.
Antenna switch: Ideal if two or more antennas are available and convenient switching between them is desired.
SWR meter: Allows antenna tests to be done – one that is correctly installed and tuned should indicate 1.5:1 or better. Some instruments can also measure the transmitter's power output.
Dummy load: Useful if doing power measurement tests.
You may hear people talking about 'power mikes' and linear amplifiers. These devices are illegal and can interfere with radio and TV reception. For this reason they are not sold by reputable dealers.
To see if the equipment is working, try calling for a 'radio check' on Channel 8 or 11 AM or 16 or 35 LSB. Or find a busy channel and say 'breaker' to join a conversation.Do this just after someone finishes their transmission so you do not cause interference and have a chance to be heard by both sides of the conversation. Introduce yourself, give your town or suburb and ask for a radio check. Also tell the other station how strong they are to you.There is no restriction on what you may talk about on CB radio.
Signal strengths are given in several different ways on the CB band.This is because of different operator preferences and differences between equipment.If you're are 'ten over' or 'twenty over' it means you're a very strong signal. The 'over' bit refers to being over S9, which is the maximum reading on a signal strength meter. Cheaper sets only have three or four LED lights to indicate strength. A report of 3 lights out of 4 is a fairly strong signal. Others simply say 'loud and clear' or 'full scale' to indicate a solid signal.
CB is not like a telephone. With a telephone you can interrupt people in mid-sentence.CB is what is known as half-duplex, where only one person can talk at a time. This is why it is very stupid to interrupt someone while they are talking.They won't hear you! Only start talking when they've finished. When two people do talk at once, listeners will hear an annoying tone (on AM), or two voices on SSB. In both cases the strongest signal will be intelligible, though if two signals are about equal strength, it will be hard to make any of them out.
Now that there are now no official government-issued callsigns, most people just make up their own. Just don't pick the same as someone else's; otherwise an on-air argument may ensue!Callsigns can either be catchy words or combinations of letters or numbers. The latter are particularly popular on SSB where operators often use callsigns issued by a CB club. A few people still use their old official callsign, especially on SSB, even though it no longer has legal status.
The vocabulary used on 27 MHz is a mixture of 1970s American trucker lingo, jargon borrowed from amateur radio and plain (and sometimes coarse) language. After a while listening it should be possible to work out what it all means.
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 but increased in popularity when equipment got cheaper. Modern UHF CB radios now have 80 channels though old 40 channel radios are still legal to use.
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.
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.
1 476.425 21 476.925
41 476.4375 * *
2 476.450 22 476.950
42 476.4625 * *
3 476.475 23 476.975
43 476.4875 * *
4 476.500 24 477.000
44 476.5125 64 477.0125
5 476.525 25 477.025
45 476.5625 65 477.0375
6 476.550 26 477.050
46 476.5625 66 477.0625
7 476.575 27 477.075
47 476.5875 67 477.0875
8 476.600 28 477.100
48 476.6125 68 477.1125
9 476.625 29 477.125
49 476.6375 69 477.1375
10 476.650 30 477.150
50 476.6625 70 477.1625
11 476.675 31 477.175
51 476.6875 71 477.1875
12 476.700 32 477.200
52 476.7125 72 477.2125
13 476.725 33 477.225
53 476.7875 73 477.2375
14 476.750 34 477.250
54 476.7875 74 477.2625
15 476.775 35 477.275
55 476.7875 75 477.2375
16 476.800 36 477.300
56 476.8125 76 477.3125
17 476.825 37 477.325
57 476.8375 77 477.3375
18 476.850 38 477.350
58 476.8625 78 477.3625
19 476.875 38 477.375
59 476.8875 79 477.3825
20 476.900 40 477.400
60 476.9125 80 477.4125
Notes on channel allocations:
1.Several channels are set aside for special uses.These are:
Channel 5 Emergency Channel
Channel 11 &nsbp; Call Channel
Channel 40 Road Channel
2.Channels 22 and 23 are used for telemetry and remote control purposed. The ACMA advises that voice communications on these channels is prohibited.
3. Repeaters transmit between channels 1-8 and receive between channels 31 and 38. Channels 41 - 48 and 71 - 78 are also allocated to repeaters. Avoid these channels for non-repeater (simplex) communications. Repeaters operating on Channel 5/35 may be used for emergency communication only. If you are near the station you are talking to, you should move from the repeater to a simplex channel (see note 5) to leave the repeater free for others who cannot communicate direct.
4. Though Channel 11 is officially the call channel, most people use repeaters for this purpose instead. Many truck drivers use Channel 40.
5.The following channels are suggested for general simplex communication:9, 10, 12-21, 23-30, 39, 49-60, 64-70, 79 & 80.
Both handheld and mobile equipment is available for UHF. Newer models cover all 80 channels and can be used with repeaters. Like 27 MHz there are now no base station transceivers available. Instead use a mobile transceiver connected to a 13.8 volt power supply and a base station antenna mounted outside.
All mobile transceivers put out the full five watt legal limit. Thus there is very little difference in communications range between more expensive and cheaper units.However the better units have extra features that can be useful. Examples include (1) ability to search all channels for activity without manually turning the channel selector (scanning), (2) a signal strength meter, (3) a frequency readout as well as channel number and (4) CTCSS tone squelch to reduce reception of unwanted signals.
Handheld transceivers vary more widely than mobile transceivers in both features and price tags.They are now the fastest selling part of the CB radio market, no doubt helped by falling prices that are only fraction of those only a few years ago.
The cheapest handhelds such as pictured above, cost $50 or less and are low-powered (500mW or so). They do not come with rechargeable batteries and cannot be connected to external antennas. If you need only short range communications, these units perform well.
Middle range UHF handhelds feature higher power outputs (1-2 watts) and/or come with rechargeable batteries and charging cradles. CTCSS subtone and voice operated transmit (VOX) are found on some models in this range. AA batteries are preferable over AAA for the longer battery life possible. These radios do not usually have removable antennas however.
Upper range handheld UHF transceivers cost up to about $400 and include most or all of the following:(1) 5 watt power output, (2) rechargeable battery pack and charger, (3) CTCSS subtone, (4) voice operated transmit (VOX), and (5) ability to connect external antenna and power. This last feature allows handheld transceivers to be operated from a car. However unless extensive use outside the car is planned, a car-mounted transceiver is easier to use and represents better value for money.
The following basic controls are found on most UHF CB transceivers:
Channel select: allows you to switch between channels. This may either be a rotary knob or up/down buttons.
On/off/volume: same function as on a transistor radio
Squelch or mute: Adjust at point where noise stops. This allows silent monitoring of channel. If someone talks the squelch is 'broken' and you will hear their voice. Disable the mute (by adjusting for hiss) if signals are weak.On handheld transceivers this function may be performed by a 'monitor' button, which unmutes the set when it is pressed.
Simplex/Duplex switch: If operating direct (no repeater) leave this switch in simplex position. To operate through a repeater select the appropriate repeater channel and switch to Duplex.
Scan: Allows the radio to search for activity across all 40 channels. The scanning will stop as soon as a busy channel is found.
Other controls you may find include CTCSS, memory, power output select and VOX.Mastery of these is not required for basic operation. The transceiver's instruction manual will explain how to use these more esoteric functions.
The antenna used has a large influence on transmitting and reception range.Larger antennas have more 'gain' than smaller antennas, so are superior for longer distance communication.Antenna gain is measured as a ratio (decibels or dB) compared to a standard reference antenna (usually called an 'isotropic radiator').The more the dB rating, the higher the gain.
Base station antennas may be verticals or beams.Verticals provide equal coverage to all points of the compass, whereas beams squirt most of the signal in one direction. Beams look like UHF TV antennas but are mounted so that their elements are vertical.Base station verticals exhibit gains of between 4.5 and 12 dB, while beams typically deliver between 10 and 15dB. This makes beams a better choice where signals are very weak. Unless communication in only one direction is required, beams should be fitted to a rotator so that they can be pointed in all directions.
Mobile antennas can be mounted on either the roo bar or roof, with a rooftop position being preferable. The centre is best, though one side of the roof will still give good results.Some antennas are 'ground independent'.This means that they can be mounted on a non-metal surface or metal pole. Antennas that are not ground independent should always be mounted on the car roof or bonnet. Antennas vary between about 16 cm and 1 metre or more in length. Again, longer antennas have more gain, with figures between 3 and 6dB being common. UHF antennas come pre-tuned, with no user adjustment (or 'SWRing') required. Base mounted springs should never be used on UHF as they will put detune the antenna.
The quality of feedline used on UHF is much more critical than on 27 MHz.The thin RG58 should only be used for short runs, such as in a mobile installation.RG58 can be used for a base station, but you could easily lose 75% of the signal before it gets to the antenna. This can easily negate the gain of your antenna and make your station perform little better than a hand-held transceiver. For this reason a proper base station installation uses RG213 (or better) cable, which is acceptable for runs up to about 15 metres. For longer lengths, or when ultimate performance is required, an even thicker cable called 9913 could be used instead.
The following accessories are in common use and can enhance the efficiency of your base, mobile or handheld 477 MHz CB station. Because of the swing to UHF, they tend to be more widely available than 27 MHz accessories.
Power supply:A power supply is required if you wish to use your CB from home.It needs to provide aregulated voltage around 13.8 volts.It should have a capacity of 2-3 amps (continuous) minimum.Those who use supplies that are too small or are poorly regulated (eg a car battery charger) will find that their signal sounds distorted on air, with hum prevalent. A good tell-tale sign of this is the dial lights on your radio – if these dim significantly when you're talking, it means your power supply isn't up to the task.
External speaker: Particularly helpful in noisy vehicles, or if you want better sound when using equipment at home.The connection is almost always a 3.5mm mono plug.
Antenna switch: Ideal for switching between vertical and beam.
Speaker/microphones & headsets: Lets you operate the radio without having to hold it.Some headsets permit VOX operation with suitable equipped transceivers.
Battery eliminator: Allows handheld transceiver to operate from car cigarette lighter.
Leather case: Gives the radio some extra protection.
Drop-in charger cradle: Allows transceiver to be charged without needing to remove the batteries.
To see if the equipment is working, try calling for a 'radio check' on Channel 40. If you are near a major highway, you will get an answer about half the time. Alternatively with the transceiver set to duplex, listen for repeaters between channels 1 and 8. If you find a busy one, put in a 'breaker' as soon as the person has finished and ask for a 'radio check'. If all is well, someone will say that 'you're working' or are 'loud and clear'. If no one is using a repeater, ask for a 'radio check'. If you're triggering the repeater you will hear a brief hiss from the radio as soon as the microphone push to talk (PTT) button is released. Try this on all repeaters (except Channel 5) to establish which are available in your area.
Repeaters are intended mainly for mobile, handheld and other stations for which simplex communication is not normally possible. If you get talking to someone on a repeater, listen to see if they can be heard simplex. This is done by quickly switching to the repeater's input channel (mostly between between channels 31 and 38). If their signal is strong, suggest moving to a simplex channel, leaving the repeater to those who need it.
UHF simplex operation is similar to 27 MHz AM.Find a busy channel and say 'breaker' to join a conversation.Do this just after the person talking finishes their transmission. This is to avoid interference and to be heard by both sides of the conversation. Introduce yourself, give your approximate area (never a street or identifiable address if at home) and ask for a radio check. Also tell the other station how strong they are to you. There are no restrictions on what you may talk about on CB.
As with 27 MHz, UHF CB is not like a telephone where you can interrupt people mid-sentence. Only one person can talk at a time. If two people try to talk at once, the 'capture effect' of FM means that only the strongest station will be audible.
Some operators use callsigns on UHF, though these appear less common than on 27 MHz. People normally use their first name or just operate anonymously. Truckie-derived CB slang is rare on UHF, and people mostly use plain language.
A 27 MHz radio will not communicate to a UHF radio. For this reason it's important to consider equipment choices wisely, as most transceivers only cover a single band (the Uniden UH-099 being an exception).
The main decision for most people is 27 MHz or UHF. If choosing 27 MHz, you will need to decide between AM and AM/SSB. On UHF the choice is between mobile and handheld, and if handheld, the desired power level.
UHF CB is the best choice for most given current activity levels and trends. 27 MHz could be better if you need (a) the cheapest possible short-distance communications (b) communications in mountainous areas or (c) the possibility (and excitement) of long-distance SSB communication.
The low price of CB radio (especially compared to other two way radio systems) is attractive, but like everything that's cheap, there are limitations. The following are things that CB radio will not do:
Long-distance outback communications: If you stick to the main roads, a UHF CB is fine. But in very remote areas where long-distance coverage is required, it is next to useless.Instead buy or hire a satellite phone or HF transceiver for the VKS-737 Australian National Four Wheel Drive Radio Network or similar.
Reliable coverage over an entire metropolitan area: Five watts is too low to permit simplex city-wide communication via either 27 MHz or UHF CB. Metropolitan coverage is possible with UHF repeaters, but these can be busy, interfered with or turned off without warning. Rather than use CB, serious business users should discuss their needs with a specialist two-way radio company, which will be able to supply equipment and provide access to wide-coverage VHF or UHF repeaters.
Privacy: CB is a public medium with dozens listening at any one time. There is nothing to stop listeners from recording your voice and putting it on YouTube for entertainment, especially if you behave stupidly (search 'UHF CB' for numerous examples). Contrary to popular belief, CTCSS does not provide private communications.If private, interruption-free communication is desired, use a mobile phone instead.
A copy of the CB radio class licence is on the Australian Communications and Media Authority website