By Jason Reilly.....

 

An often asked question heard on the CB bands by newcomers to the hobby goes something like “what is best: UHF or 27MHz CB, and what mode - AM, FM or SSB?” The answer is not as simple as you might think. It’s a matter of ‘horses for courses’; what might be best for you, might not suit your buddy down the road.

 

 

The 27MHz CB service:

 

Equipment for 27MHz can generally be bought cheaper than that for UHF. At the cheap end of the scale, you can buy an AM only 27MHz CB, which would be fine for chatting between parties located not too far apart, such as within your surrounding suburbs, or between cars or trucks travelling together on the road. In fact, channel 8 AM is recognised as the ‘road’ channel, but tends not to be used these days. AM (Amplitude Modulation) here refers to the method your voice is ‘impressed’ onto the radio waves. The big drawback of AM is that it is very susceptible to noise, and is not a very efficient way of transmitting your voice; only one eighth of the power of your transmitted radio signal is actually used to carry your voice to the other end. The bonus for AM is that it is simple and cheap, and sets can be made quite small. Expect to pay about $80 to $130 new depending on the features & quality you want, down to between about $10 and $50 for a second hand unit.

 

 

If you want to overcome these drawbacks, you would buy a 27MHz CB with SSB (Single Side Band) as well as AM. Single side band is a different, more efficient way of transmitting your voice. It is less susceptible to noise than AM, and regulations governing the allowable output power of CB radios allow a higher output power using SSB, thus allowing a longer reach for your signal. The drawbacks of SSB is that the equipment is not as compact, more expensive, and the voice quality while very understandable, has a slightly unnatural quality to it.

 

 

Antennae for 27MHz are, generally speaking, considerably larger then their UHF counterparts.

 

 

Under normal conditions, you can expect about a 10 to 15 km range for your AM only CB between base stations, and up to 80 km for SSB mode between base stations.  Roughly divide by three these distances for communication between mobiles There is a condition known as ‘skip’ which will allow your 27MHz signal to travel much farther distances, perhaps many thousands of kilometres. Every eleven years or so, the sun goes through a cycle of producing sunspots, which charge the ionosphere, causing it to become somewhat reflective to 27MHz CB signals, but not for UHF signals. The 27MHz signals travel from your antenna up to the reflective ionosphere and ‘bounce’ off it back to earth some hundreds or thousands of kilometres away. During such conditions the channels become very crowded, not only from people looking to contact people from long distances, but from other people who are just talking between themselves in their own area - also thousands of kilometres away!

 

 

You will be paying between $180 and $300 for a new SSB 27MHz CB again dependant on features and quality, and $40 to $150 or maybe a tad more for second hand units.

 

 

The UHF CB Service:

 

 

UHF CB equipment is generally more expensive, but not tremendously so. Unlike 27MHz equipment, UHF CB comes in one flavour only: FM.  Frequency Modulation, or FM, is a very crisp, clear and efficient way of transmitting your signal, and suffers less from the effects of noise than does AM or SSB.

 

 

The higher frequency, and thus, shorter wavelength of UHF CB (477MHz at about 0.6 meters' wavelength as opposed to 27MHz at about 11 metre's wavelength) means shorter, more convenient sized antennae which can lead to building practical antennae that offer ‘gain’ and much less atmospheric and man-made noise. On the other side of the coin, UHF signals do tend to suffer more attenuation, that is, the signal becoming weaker, when passing through buildings, trees, or passing over difficult terrain.

 

 

UHF signals also do not ‘skip’ or bounce off the ionosphere and thus do not regularly travel the large distances that 27MHz signals can.  Interestingly, there is an entirely different atmospheric condition that can cause UHF signals to travel further than they normally would, called tropospheric ducting.

 

 

Generally, UHF CB has a range of about 100 km between two well located base stations, or about 15 km between mobiles, however these distances will vary given the height of and terrain between two stations, much more so than 27MHz stations. The voice quality is excellent, even better than the telephone at times, and the quality is maintained almost to the fringes of coverage, rather than the slow but progressive increase in noise and general degradation of AM and SSB on 27MHz CB.

 

 

One important feature on UHF CB is the availability of repeaters - a device suitably located on a mountain or hilltop so that two UHF CB stations can relay their signals through the repeater and communicate much further than they normally.  With this arrangement, two mobiles some 100 or 200 km apart can communicate, and even further with base stations, but this again is entirely dependant on how well the repeater is located, and the location of the two mobile or base stations using the repeater.

 

 

Prices for new UHF CBs range from about $100 for small, low power handhelds, to $600 or more for feature-rich mobiles or handhelds with blisteringly hot performance and quality. Halve these prices for second hand units.

 

 

What is going to give me the greatest range?

 

Without doubt, a 27MHz SSB radio will offer you the greatest range when conditions are right for ‘skip’; your signal will typically travel some thousands of kilometres, but it is completely dependant on the conditions. One day, there may be no ‘skip’ at all, the next, the skip might be running well between Victoria and Queensland, the next day between Victoria and Western Australia. Then there will be long periods, sometimes for a few years, when conditions do not produce skip at all, or at least very infrequently. Without the benefit of ‘skip’ you can look at about 80 or maybe 100 km range between two well equipped SSB 27MHz base stations.

 

 

UHF CB offers very consistent clarity of communications across a local area, say out to 40 km, but can travel up to 100 or more km with well equipped and well positioned base stations. UHF CB is less affected by noise, both atmospheric and man-made, and this is a very attractive feature for many operators. Repeaters open up a whole new ball game, with crystal clear communications possible between stations using a repeater for perhaps 200 km.

 

 

27MHz AM CB is really only a very local service, and is greatly affected by noise, but the big advantage is that it is very cheap.

 

 

How about we compare, blow by blow, the pros and cons of UHF and 27MHz CB:

 

1. Cable losses at UHF CB are greater than at 27MHz, but countering this is that antennae at UHF tend to have higher gain than an equivalent sized 27MHz CB antenna.
    

2. 27MHz SSB is a very efficient way of transmitting your voice, but then again, so is the FM of UHF CB
    

3. The output power of a 27MHz SSB is 12 watts compared to 5 watts for UHF CB, but there is less atmospheric and man-made noise at UHF CB which tends to even things up a bit.
    

4. 27MHz CB signals travel through obstructions and tends to ‘bend’ around difficult terrain better than UHF CB, but UHF CB will bounce and reflect off large buildings and hence be heard a bit better deep within the ‘concrete canyons’ of a major city centre.

 

 

All in all, UHF CB and 27MHz CB tend to be reasonably equal - where one looses out, the other does better. That is until you add a repeater into the picture; this will extend communications into an area where neither UHF in simplex mode or 27 MHz SSB would have no hope of reaching.

 

 

So, what is right for me? UHF or 27MHz? AM, FM or SSB?

 

There is no simple answer to this question. You need to look at where you are operating from, who you want to talk to, what features you want, and of course what you want to spend. Other things to consider might be: are you allowed to erect outside antennae on your rental property; are you willing to have a less attractive looking outside antenna that offers some gain; or is there any other unusual requirement that would clearly indicate a preference of one type of CB service over another?

 

 

If you are looking for short range, cheap communications, then look no further than an AM only 27MHz CB. At the opposite end of the scale, for someone who wants to talk over huge distances as a hobby, then SSB 27MHz CB is the go. Those users who want clear, reliable, medium range communications would do well to look at UHF CB. For features like scanning, SelCall etc UHF CB is the best bet. If you have had bad experiences with interference to your neighbours TV, then UHF would be safest. Depending on your area, if you just want to pick up the microphone to chat and make friends, 27MHz seems to be more relaxed, but in some areas UHF can be just as informal. UHF also seems to have been adopted more readily in the country, even taking on the role of a medium range ‘bush telephone’ at times. 27MHz SSB CB would be best for those looking to communicate into or out of a deep valley, but don’t ignore UHF where a repeater may be even better, or there might be a hillside to bounce your signal off.

 

 

Some Pro's & Con's for you to think about: