Fullscreen HTML5Med Res (??MB)HTML4

Understanding the world of CB radio Have you wondered about becoming involved with CB radio? Perhaps you are thinking about buying a CB radio for that next country trip. If so, this article for you. It gives the background and history of CB radio and talks about the 2 71\.1Hz and UHF bands. By HERB ZALLNER CB Radio as we know it today had its origins in the late 1950s, in the USA. On 11th September, 1958, the FCC inaugurated a "Class D" service, allocating 23 channels between 26.965MHz and 27.255MHz. The service was designed to be used for specific purposes, none of which related to hobbyist use. Interest in the new service soon grew and within 12 months, over 40,000 operators had been licensed. This service ran until 1971 when it was dissolved and users were allocated other more specific services. In 1973, the USA was in the grip of an oil crisis. Fuel supplies were scarce and a 55mph speed limit was brought to bear. For "truckers", who had al16 SILICON CHIP ready been subjected to a price and wage freeze at a time of rocketing costs, the speed limit was the last straw and they went on strike. Millions of Americans saw news bulletins showing truck drivers with 2way radios organising their blockades of tollways and interstate highways. Motorists bought CB sets to hear the truckers telling one another, after· the strike was over, where scarce pet_rol was available and where highway patrol cars could be found. Citizen's Band radio had been born. By 1976, the FCC found it impossible to police the number of licensees and "pirates" occupying the CB service and decided to lift most restrictions, including one which had previ- ously prevented hobby use of the band. The result was incredible. Within the next eight months, one million licenses were granted and another million were granted within the next three months. The US CB band contained 23 channels in the 2 7MHz band and allowed 4 watts of AM power. The transceivers used a method of frequency generation called crystal synthesis or "crystal plexing", which utilised 12 or 14 crystals and three oscillators to cleverly create both transmit and receive frequencies. This was a great saving in cost over the previous crystal controlled sets , which had used 46 crystals. At last, affordable transceivers were Above: the Uniden Pro 810e is an AM/ SSB base station for the 27MHz CB band. Its features include separate volume, squelch, RF gain & clarifier controls, a noise blanker switch, a 7W audio amplifier, a PA facility plus external speaker provision, and an illuminated signal/RF meter. (Dick Smith Electronics). Table 1: 27MHz CB Channels 18-CH Set 1 2 3 4 5 Designed for in-car use, the Uniden PRO 640e is a top-of-the-line AM/SSB-CB radio. Among its many features are digital readout of channel number; a LED bargraph for signal strength, RF output & SWR; & direct access to emergency channel 9. It covers all 40 channels in the 27MHz band on AM, LSB & USB. (Dick Smith Electronics). available to the general public and by 1977 several organisations had made submissions to the Australian government fo r the intro duction of an official CB band. In the meantime, this did not prevent the sale an d consequential illegal use of tens of thousands of CB transceivers using the US 23-channel system while the various submissions w ere under review. A further complication arose in 1976 when the USA service was expanded to 40 channels to cater for increased demand. Finally, the Australian governm ent decided to implement a compromise 18-channel system proposed by Dick Smith as the best alternative for local conditions. This channel system was designed to allow the maximum number of channels without causing interference to existing services. Table 1 shows the 18 and 40-channel frequency allocations. After several years of successful operation of the 18 channel system , Australia followed the USA and implemented the same 40 channels in the 27MHz band. SSB operation by this time was allowed and despite the regulatory restriction of" communications only within Australia", the tantalis- ing possibility of communicating with another country added more appeal to users of the service. CB became an outlet for social communications, allowing users to communicate with others at no cost (other than the initial licensing fees) and without th e burden of the technical examination required of amateur operators. After all, most enthusiasts claimed that the radio spectrum was a national resource and that they should not be denied the right to use it for social means. The service also provided low-cost communications for business people, even considering the lack of privacy and unpredictable communications range, a result of operating on the 27MHz band. In 1977, Philips Industries proposed a "personal radio" band utilising part of the UHF spectrum and using FM as the transmission mode in the 476477MHz range. It was envisaged that this would eventually replace the 2 7MHz band service and, in the meantime, ease congestion of the 27MHz band. It would also allow business users the same communications facilities as the 2 7MHz service while allowing some reuse of frequencies, as a result of the 10-25km "line of 6 7 8 9 10 11 12 13 14 15 16 17 18 40-CH Set Frequency 1 2 3 4 5 6 7 8 9 10 11 26.965 26.975 26.985 27.005 27.015 27.025 27.035 27.055 27.065 27.075 27.085 27.095 27.105 27.115 27.125 27.135 27.155 27.165 27.175 27. 185 27.195 27.205 27.215 27.225 27.255 27.235 27.245 27.265 27.275 27.285 27.295 27.305 27.315 27.325 27.335 27.345 27.355 27.365 27.375 27.385 27.395 27.405 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 sight" coverage achievable with a UHF transceiver. In the same year, Philips introduced their "FM320" 40-channel UHF personal (CB) radio transceiver which , despite its high price, was an instant success. Subsequently, in November 1979, Philips also installed the first UHF CB repeater at Lysterfield in the foothills of the Dandenong ranges. Approved under an experimental JULY 1992 17 Retailing for around the $450 mark, the Pearce-Simpson UF-2020 UHF CB has microprocessor control to provide scanning & a range of other specialised functions. The front panel can be mounted remotely, so that the main body of the rig can be located anywhere within the vehicle. license issued by the DOC, this allowed enhanced coverage beyond the normal simplex limitations of a UHF transceiver, thereby adding considerable appeal to the UHF service. Thereafter followed an enormous influx of imported UHF transceivers and the formation of various CB clubs, which subsequently installed UHF repeaters all over Australia. In many cases, UHF CB became a viable alternative to commercial 2-way radio, although this was not the intention of licensing authorities. Table 2 lists the channel frequencies in the UHF CB band. Today, there are over 400,000 licensed CB operators in Australia, proof of the success of the service. Both the 2 7MHz and UHF bands coexist, serving hobbyists and commercial users alike. Emergency monitor- ing services exist in most country towns and outback travellers use CB radio for communications, as do farmers, truck drivers, commercial users and many country police officers! Selecting a CB set The price of a CB transceiver ranges from less than $50 for a basic AM transceiver to several hundred dollars for a sophisticated SSB or UHF "rig". Don't make a rush decision when buying equipment; your purchase deserves some consideration. If the intended application is city use only, UHF offers FM clarity and repeater enhanced operation. Small antennas can be used and there are plenty of mobile transceivers from which to choose. If the application involves outback communications, then an AM/SSB The Uniden Sundowner is typical of CB radios designed for the UHF band. It covers all 40 channels, features digital readout of channel number & features duplex switching for operation through a repeater station. (Dick Smith Electronics). 18 SILfCON CHTP transceiver, able to take advantage of the 27MHz propagation or "skip" conditions, is the best choice. After all, when calling for help, the larger the audience, the better! Also, a longer antenna can more easily be tolerated when driving in the country, as there are less obstructions to interfere with a 3-metre whip than in the city. Base stations are available in both 27MHz and UHF, although the 27MHz models are somewhat better presented and often include SWR and output power metering, in addition to an inbuilt 240V AC power supply. Having selected a suitable transceiver, a suitable antenna must be chosen. The most popular 2 7MHz mobile antenna is the helical whip. By winding a quarter wavelength of wire on a fibreglass whip, antenna makers have been able to achieve reasonable matching, radiation pattern and mechanical flexibility. Both ground dependent and independent antennas are available. If the antenna is to be mounted on a metallic car body, a ground dependent antenna is necessary. If the mounting position is such that a good groundplane cannot be achieved (critical if the antenna radiation pattern is to provide any gain), then a ground independent antenna should be used. Typical mounting locations for a ground independent antenna would be the rear bumper, mirror mounts or the bullbar of a motor vehicle. Base station users are well catered for, with high gain (9dBd) collinear antennas and directional Yagi antennas available for UHF users. 27MHz operators can utilise full length halfwave antennas and more adventurous operators have even been known to install rotatable Yagi antennas (quite an undertaking at this frequency)! Most CB antennas come equipped with coaxial cable, however the quality of the cable used for UHF installations is critically important. Coaxial cable used at UHF can be used at 27MHz but the reverse is not always true. the loss of signal through a low quality coaxial cable at 27MHz is of little consequence but at UHF it can reduce transmitter output power and receiver sensitivity by 50%. Likewise, coaxial connectors are important, as they provide impedance matching between the transceiver and the antenna. For UHF, premium qual- ity connectors must be used to minimise losses. Transceivers installed in motor vehicles require careful mounting and connection. Care must be taken to ensure that the transceiver is mounted securely, so that if an accident occurs, it remains mounted on the dashboard, where it cannot harm the occupants. Power connections should be made directly to the car battery, eliminating the possibility of vehicle accessory noise being fed to the transceiver. All CB transceivers sold these days are negative earth, allowing the chassis to be directly connected to the vehicle body. The suppression of ignition interference is of great importance to 27MHz users, who do not have the benefit of the intrinsic noise immunity afforded by FM. Ignition noise can either be radi- The "Sea Simba" is a 27MHz CB radio specifically designed for marine work. It has 10 channels, 5W output power, a loudhailer/PA, automatic noise limiting, and adjustable RF & mic. gain. (Hatadi Electronics). Designed for the serious operator, the Pearce-Simpson Super Cheetah MkIII boasts an in-built scanner, 40-channel AM/SSB operation & a noise blanker. It's sold by Jaycar Electronics. ated or conducted into a CB transceiver. The use of suppression spark plug leads, grounding the end of the vehicle exhaust system (which can act as an antenna, hung under the body of a car by rubber bands) and earthing the bonnet by bonding the hinges using copper braid, will generally eliminate radiated ignition noise. Direct connection to the vehicle battery is the best method to eliminate conducted noise. Licensing One license per transceiver is required for the operation or possession of a CB transceiver. Licenses are easily obtained from the Department of Transport and Communications by filling in the appropriate form (DOC5 7A) and payment of the appropriate fee. DOTAC will then issue a callsign and an operating guide. CB operation is permitted on a non interfering basis. This means that if interference is generated by a CB operator, DOTAC can request the operator to minimise interference by restricting operations until the technical reason for the interference can be determined and a cure implemented. In some states of Australia, it is an offence for drivers to use radio communications equipment while driving. Finally, all equipment must be type approved, in the case of 27MHz equipment to DOTAC specification ECR312 and for UHF, ECR250. As unapproved CB transceivers are prohibited imports, virtually none appear for sale on the Australian market. CB etiquette As any shortwave listener knows, CB and amateur operators have developed a "language" of their own. Table 3 shows what are called "10codes" and "Q" codes. The idea of using these codes was originally as an aid to communications in poor conditions. These days they are used more as jargon. As the CB bands can be shared by everyone, certain band plans have been devised to ensure that, for instance, SSB does not interfere with AM stations and so on. Basically, the 27MHz plan, part of which is law, states that only AM can be used from channels 1-14 and that SSB can only be used from channels 15-40. Also, certain channels have been dedicated for specific uses as follows: Table 2: UHF CB Channels Channel Frequency 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 476.425 476.450 476.475 476.500 476.525 476.550 476.575 476.600 476.625 476.650 476.675 476.700 476.725 476.750 476.775 476.800 476.825 476.850 476.875 476.900 476.925 476.950 476.975 477.000 477.025 477.050 477.075 477.100 477.125 477.150 477.175 477.200 477.225 477.250 477.275 477.300 477.325 477.350 477.375 477.400 34 35 36 37 38 39 40 Use Emergency Call channel Emergency Road channel Channel 8: AM only. This is the highway channel. It is used by truck drivers, travellers and base stations along main rqads to pass information relating to traffic conditions. Channel 9: AM only. This is used as the emergency channel and is monitored by rescue and volunteer groups around Australia, who have fast access to police, fire, ambulance and emergency services. Channel 11: AM only. This channel has been allocated "call channel" staJULY 1992 19 Table 3: The Language Of CB Radio 10.100 - rest stop; often interpreted as rest room stop! THE COMMON 10-CODF;S 10.1 - poor reception; have difficulty receiving you 10.2 - good reception; receiving you well 10.3 - this channel in use, stop transmitting 10.4 - acknowledgement; message received 10.5 - relay message 10.6 - I'm busy 10.7 - closing down (usually temporary close down) 10.8 - back on after closing down 10.9 - repeat what you just said, repeat last over 10.1 O - ready now, was busy 10.13 - please advise weather, road conditions 10.18 - anything for me? 10.20 - location (same as 0TH); often used as "hometwenty" or just "twenty" 10.21 - call by telephone 10.23 - standby (same as ORX) 10.27 - I am moving to channel. .. 10.28 - identify; what is your callsign (same as ORZ)? 10.32 - signal check; usually used to give signal reports 10.33 - emergency traffic at this station 10.34 - in trouble, need help 10.36 - correct time (you never get it!) 10.41 - go to channel ... (same as OSY to .. .) 10.44 - I have a message for ... 10.50 - break channel 10.77 - no contact, not receiving you, negative contact Looking for an economy handheld model? This unit from Dick Smith Electronics sells for around $100 & comes fitted for 1-channel operation. 20 SILICON CHIP 10.200 - police needed at... THE COMMON 'Q' CODES ORA - name or handle (what is your name; my name is ...) ORB - how far away are you? ORG - what channel am I on? ORL - busy (I am busy; are you busy... ) ORM - interference; generally from other stations ORN - natural or noise interference; static, car ignition etc ORP - low power (applies to those who have a high power/low power switch) ORT - going off the air; to stop transmitting ORU - nothing for you (or have you anything for me?) ORV - ready? - I'm ready! ORX - standby ORZ - what's your callsign? or who's calling? OSA - signal report (5 by 9, or 4 by 5 or whatever) OSB - fading or "flutter' on signal OSL - acknowledgement; same as "ten-four" and "roger". Used to affirm receipt of message or information. Hence, OSL cards OSO - contact OSP - to relay a message OSY - change channels or frequency 0TH - location (same as 10-20) OTR - correct time is ... tus and is used to establish initial contact. Once contact is established, operators are required to move to another channel to continue their conversation. Channel 16: LSB (lower sideband). This channel has been designated the "SSB call channel". Only LSB is used and once contact has been established, operators must move to another channel. Channel 35: LSB. Secondary SSB call channel, particularly for stations desiring long distance "DX" contacts. UHF operators have also dedicated specific channels for certain usage: Channel 5: UHF emergency channel. In mos.t capital cities, a repeater operates on this frequency (channel 5 receive, channel 35 transmit) to provide greater coverage of emergency services. Channel 11: UHF call channel. Channel 35: Secondary emergency channel. As well as being the input frequency for emergency repeaters, it can also be used for simplex emergency communications. Channel 40: UHF highway channel. In addition, UHF repeaters operate from channels 1-8 and 31-38 and can only be accessed using the duplex mode on UHF CB transceivers. As each channel is separated by 25kHz, this 30 channel "split", when using the repeater mode, equates to a fre quency difference of 750kHz. Good operating practice dictates that repeater users keep transmissions short. In fact, all UHF CB repeaters are fitted with a time-out function, which automatically switches the repeater transmitter off if the input signal is held up for too long. It is also good etiquette to always wait a few seconds after the audible repeater "tail" drops out before re-transmitting through a repeater. This gives other stations the opportunityto "break in", before they travel outside the range of the repeater. It is wise to check the input channel of the repeater during a conversation, just in case the other station can be heard at good signal strength. If this is the case, the stations should move to a simplex channel to leave the repeater free for others. SC