Do you need a CB radio?

First, a history lesson...

Citizens’ Band (CB) radio has been with us in Australia since the early 1970s. Originally 27MHz frequency, CB radio in Australia transitioned to 477MHz UHF in the late 1970s, with 40-channel bandwidth.

In 2011, the demand for more channels gave rise to 80-channel, Narrow Band CB. At the same time, the number of repeater channels was doubled. This channel expansion wasn’t done by increasing the bandwidth to accommodate more channels, but by reducing channel spacing.

Forty-channel, Wide Band sets have a channel spacing of 25kHz and transmit a signal that is 16kHz wide (8kHz either side of the channel). When there were only 40 channels this was fine, as there was 25kHz between channels, providing a 9kHz buffer.

However, when the 80-channel band was introduced, this changed. Because bandwidth remained the same, but accommodated twice as many channels, there was only 12.5kHz between the old and new channels.

Backdown on UHF ban

To avoid prolonging perceived interference conflict between the two systems, the Australian Communications and Media Authority (ACMA) planned to phase out approval for 40-channel UHF radios in July 2017. However, in February of that year, the scheduled ban was removed.

Retail sales of new 40-channel radios ended, but existing radios were allowed to work in bandwidth being increasingly dominated by new 80-channel sets.

The reason for ACMA’s backdown was due to vocal complaint from owners of thousands of 40-channel radio owners on farms and in trucks, caravans and businesses throughout Australia. Many UHF CB users were upset by the original decision to make 40-channel radios illegal and many more were completely unaware of the need for the change to 80-channel units.

Some trucking fleets said that upgrading to 80-channel radios would have cost them tens of thousands of dollars.

In February 2017 the manager of spectrum licensing policy at ACMA, Dominic Byrne, said the two systems were working well alongside each other, so the Authority had decided to remove the requirement for all users to upgrade to 80-channel UHF sets.

“Based on both some dialogue we’ve had with CB users and some monitoring of the CB channels we’ve been doing … we don’t think that there’s any harm from the continued operation of the 40-channel units,” he said.

Channel integration in the real world

We’ve checked out the mixed use of 40-channel and 80-channel radios in convoy testing and have had varied results.

In some cases there were only speaker volume issues, as well as the narrower choice of channels that both radio types could use, but in other cases we had considerable interference and static when the 40-channel units transmitted to 80-channel sets.

When a signal on one channel extended up 8kHz and another signal on an adjacent channel extended down 8kHz the channel between those two could be swamped by signals from both sides.

The situation seemed to be exacerbated by people not having appropriate aerials for the terrain or using old handheld radios for vehicle to vehicle talk.

As we’ve seen, when the Wide Band 40-channel network was expanded to 80-channel Narrow Band this was achieved by ‘squeezing’ the 40 additional channels in between the existing ones. It wasn’t a case of the existing 40 getting 40 more stacked on the end.

Channels 41 to 80 are located halfway between each of the original channels, so channel 41 is between channels one and two. The original 40 Wide Band channels are part of the Narrow Band network, but retain their original frequencies.

When a NB radio receives a transmission from a WB radio on the same channel, the audio may sound loud and speech can be distorted. When a WB radio receives a transmission from a NB radio on the same channel, the audio may be quieter compared to a WB radio’s transmission.

When using a WB radio on channel 10 and a NB radio is using channel 49 or 50, which are adjacent to channel 10, the WB radio may hear the NB radio as distorted and off frequency, where a quality NB radio may not open its squelch to the WB radio.

Aerials: Bigger isn’t always better

Of course size matters, but it’s a common misconception that a tall CB aerial gives the longest reception and transmission range in all situations. Certainly a tall aerial works better than a shorter one in open, flat country, but it’s not as effective as the shorter aerial in hilly or undulating terrain. How can that be?

Aerial efficiency is defined by ‘gain’. Gain is an electromagnetic term that describes how well an antenna converts electrical power into radio waves in a specific direction when transmitting and the reverse function when receiving.

Gain is measured in ‘decibels’ (dB), which is somewhat confusing, because noise-level measuring and audio equipment also use decibels as a unit of measure. However, dB is a general unit that can be applied to nearly any force with amplitude or power and isn’t reserved exclusively to describe the loudness of sound.

Gain, in the case of aerials, is measured in comparison with an ‘isotropic’ aerial, which is a theoretical aerial, having the same intensity of radiation and reception in all directions. So, an antenna with 0dB would evenly transmit and receive radio waves to and from all directions, like a perfect sphere.

Such an aerial would have great coverage in all directions, but would not have much range.

More gain than 0dB is desirable to increase range and that’s why CB aerials are described variously as having 3dBi, 6dBi or 9dBi gain. The ‘i’ in the description is the comparison with ‘isotropic’.

The short and long story

However, as usual, there’s a catch. To increase aerial range the incoming and outgoing radio waves become limited in focus. The more gain and therefore, range, the smaller the area of coverage at that distance. The isotropic theoretical spherical coverage increases greatly in diameter, but narrows in height to a gradually flattening torus (donut) shape, with the aerial at its centre.

On flat terrain, that donut radio-wave coverage isn’t a problem, because the focus often reaches as far as the horizon, but the accompanying diagram shows the real-world limitations of high-gain 6dBi and 9dBi aerials in hilly country.

It’s clear that the narrower band produced by a high-gain aerial may pass over the top of another vehicle aerial, where a lower-gain aerial will contact it.

So, for optimum CB radio coverage in all conditions, you need a short aerial and a long one. A log truck driver, for example, may need a tall aerial on the run from the log dump back to mill, but require a shorter aerial when talking to the loader operator in hilly terrain.

One alternative is to opt for a ‘twin’ kit, such as Uniden’s or GME’s packs that come with a single coil-spring mounting and two screw-on aerials; a 725mm one with 3dBi gain and a longer, 1200mm one with 6.6dBi gain. You swap the aerials to suit the terrain, which is easy enough to do on a ute 'roo bar, but not so easy if your truck CB aerial is fitted at roof height.

Some truckies fit two aerials to their vehicles, spaced as far apart as possible, to avoid interference, using a switch to change between aerials. Oricom has taken that a step further, with a twin-aerial-specific CB radio that automatically switches between aerials, without user intervention.

Avoiding interruptions

Because of its citizens’ band nature, CB radio is ‘open’, meaning anything you broadcast or receive can be heard by any receiver on that channel. That’s a good thing, if you’re looking for important information or emergency assistance, but it’s often just a nuisance.

When we get into new road-test trucks these days we turn off the CB radio more often than not, because the rubbish that’s usually broadcast is annoying and distracting.

In tightly controlled radio environments, such as Marine Rescue and the VKS-737 HF network, voice traffic is much less and users are much more disciplined, with protocols that ensure some degree of privacy.

For the CB network, Continuous Tone-Coded Squelch System (CTCSS) doesn’t give you privacy, but can stop your vehicle to vehicle conversation being interrupted by outsiders.

CTCSS triggers an inaudible tone each time you transmit, recognised by a receiver that is switched to receive transmissions that start with that tone.

It doesn’t make your chat private, but it does cut out unwanted contributions and can be handy if you’re in a truck convoy and don’t want the four-wheelers involved.

Complicated radio rules

The popularity of CB radios means that nearly every bush-travel vehicle has one and this familiarity can breed contempt. There are strict laws governing the use of citizens’ band radios and hefty fines or jail time can apply for misuse.

For example, interfering with life and death broadcasts on the designated emergency channels five and 35 can be a very serious offence.

We’re indebted to Duoro, who operate the CB repeater station at the NSW mountain town of Kurrajong, for the accompanying illustration of channels that can be used for general talk communications and those that cannot.

That chart shows what looks like a random selection of channels you can use and those you can’t. Obviously, it would be easier for CB users if the usable channels were in a separate block, away from the channels that can’t be used, but that’s not how bandwidth operates, unfortunately.

You can use 43 channels: 9-30; 39 and 40; 49-70 and 79 and 80 for voice communications in simplex mode (talk and receive in one-voice-at-a-time succession) and 32 channels: 1-8,41-48, 31-38 and 71-78 for repeater-created duplex mode (telephone-like talking).

Repeaters are ground stations that receive and re-transmit voice signals, to overcome poor reception. To access duplex mode you select it on your radio and the display shows DUP, RPT or a repeater icon.

Using repeaters can be a boon in poor-reception areas and there are hundreds of them around Australia. You can search on-line for current CB UHF repeater locations.

Channel 10 is now the common 4WD communications channel.

Etiquette dictates that Channel 11 is a call channel only, so after making contact on that channel, you should move to another one for conversation.

Channel 18 is the preferred caravan communications channel.

Channels 22 and 23 are for data, Selcall and telemetry only.

Avoid using Channels 29 and 30 in some areas, because they’re used for information broadcasts.

Channel 40 is the truckies’ channel and is unfortunately often plagued by obscene language, making it off-limits to many travelling families who might otherwise like to exchange info with truck drivers.

Channels 61-63 are unallocated future channels that can’t be used.

The CB network is a blessing in this wide brown land and let’s hope that proper use stops the regulators from fiddling with it.

Also read:

How to stay connected in the Outback