UHF CB
UHF CB is a class-licensed citizen's band radio service authorised by the governments of Australia, New Zealand, Vanuatu, and Malaysia in the UHF 477 MHz band. UHF CB provides 77 channels, including 32 channels (16 output, 16 input) allocated to repeater stations. It is similar in concept to 27 MHz CB Radio in the United States. Equipment. User equipment designs are similar to commercial land mobile two-way radio, except the maximum legal output power is 5 Watts. External antennas are permitted and commercially manufactured antennas have gains as high as 12 dB. Handheld transceivers (handy  talkies) are permitted and have transmit power from 500 mW to 5 W (full legal power) and are relatively cheap compared to full-sized transceivers. Operation in the band is restricted to modes F3E and G3E (FM or PM of analogue voice telephony) except for channels 22 and 23, which are data modes only. Licensing. Class licensing means that users do not have to apply for a licence or pay a licence fee; however, they must comply with the regulations of the class licence. It is illegal to use non-standard radios purchased from overseas because they interfere with licensed  land-mobile services. This includes overseas personal radio service devices because they do not share the same band plan, power output and channels as UHF CB. Care must be taken when importing radios from overseas to ensure they comply with local regulations. Approved radios are identified by an Australian standards "C Tick", usually found on the tag or sticker of the radio. Scan. Many UHF CB radios allow the user to scan channels to find a conversation. Several different scan modes may be provided: Open Scan scans all 80 channels to find an active conversation. Some radios allow skipping selected  channels when scanning. Group Scan scans a small number of selected channels. For example, a caravanner travelling around the country may choose to group scan Channel 40 (Road Channel), 18 (Caravan Channel) and 5 (Emergency Channel) so they will hear any conversations relating to their travels. Priority Scan allows selection of a "priority" channel whilst scanning a handful of selected channels. This could be useful in a convoy of cars where vehicles can set their own convoy channel as a priority channel whilst scanning the designated road channel for traffic updates, if a member from their convoy speaks, the radio  will always switch back to the priority channel even if someone is speaking on another channel. Selcall. Selective calling (Selcall) allows a radio to call another radio using a sequence of tones, usually presented to the user as a series of 5 numbers. UHF CB radios can be set to be completely silent until they receive a series of tones matching a pre-programmed sequence. Radios which have this feature usually indicate that a call has been received by emitting a number of beeps and by opening the squelch. The popularity of selcall has dropped since the introduction of CTCSS . CTCSS. Continuous tone coded squelch system (CTCSS) allows a group of radios set with the same tone to converse on a channel without hearing other radios using that channel. CTCSS can be used to silence a radio until another radio with the same tone transmits. This allows monitoring of a channel for transmissions from radios set with the same tone without hearing other conversations that use different or even no tone. The use of CTCSS is not permitted on UHF CB repeaters or the designated emergency channels. Repeaters. Repeaters extend the range of transmission by receiving and automatically rebroadcasting a  transmission using an antenna located in a high location, normally the top of a mountain, tall building or radio tower. Sometimes a transmission range of over 100 kilometres (60 miles) can be achieved through the use of a repeater. Repeaters are on channels 1–8 and 41–48 and the duplex button should be pressed to access the repeater. Signage. It is common practice to install signs at the rear of camper vans and caravans, worksites, roadworks, regional highways, national parks and heavy vehicle checking stations to advertise a UHF channel to communicate on. For example, during the widening of the M1  Pacific Motorway between Sydney and Newcastle, contractors installed "UHF 29" signs at the entry point to each worksite. Channel use. Legally restricted channels. The following channels are legislated as a part of the ACMA UHF CB Class Licence. Channels used by consensus. The following channels are not legislated as a part of the class licence however are used for the following purposes by consensus. Users should be aware that UHF CB channels 31 to 38 and 71 to 78 are the 'input' channels for repeaters. Users should avoid using these channels to avoid interfering with repeaters. If a repeater is  to be used, switch to 1–8 or 41–48 and press the duplex button. UHF CB band plan. Expansion to 80 channels. On 27 May 2011 the channel spacing on UHF CB was changed, allowing the band to expand from 40 channels to 80 channels. Due to data channels 22 and 23 occupying 25 kHz bandwidth, the expansion effectively allows the use of 77 channels, as channels 61, 62 and 63 are reserved. ACMA originally intended to make older 40 channel UHF radios on the 25kHz spacing illegal to use from June 2017. However, in February 2017, it reversed this decision  after determining that the two systems were working well alongside each other. Current UHF CB band plan (80 Channels). General chat channels are used in simplex mode, repeater channels must be used in duplex mode. If you are not using a repeater it is recommended to choose a "general chat" channel. New Zealand. New Zealand offers a similar PRS service. New Zealand's Personal Radio Service (PRS) and 26 MHz Citizens Band radio are very similar to Australia's UHF Citizens Band and 27 MHz Citizens Band services. The New Zealand Government's Ministry of Commerce introduced the UHF PRS  in 1996 to allow for freely available short-range wireless communications outside the 26 MHz CB band. The UHF (but not VHF) band was selected due to its ability to withstand atmospheric and groundwave interference unlike the existing 26 MHz allocation.