Single-site communications involves the use of communications within an area covered by one base station site.

Applications: used within mines, construction projects, rail, farms and remote communities, allowing communication as part of a two-way radio system.

Single-site systems can be broken down into two categories: simplex and duplex systems.

Simplex systems

Simplex systems require no fixed infrastructure and are predominantly used for line-of-site communications over distances of 1km or less.

For short-distance communications, often the most effective solution is to use stand-alone personal and vehicle-mounted transceivers with no additional infrastructure. There are two broad categories of this style of communications: UHF CB Radio and Private Mobile Radio (PMR).

UHF CB Radio

UHF Citizen's Band Radio (CB) is a publicly-accessible set of radio channels (40 are provided for in Australia), and no user license is required for these systems.

Advantages:
• cheap and in plentiful supply
• no licensing requirements
• used extensively in mining, construction, agriculture and transport sectors

Disadvantages:
• No privacy
• Conversations are often interrupted by the general public, particularly in populated areas
• Low power used on transceivers (a requirement by law) leads to reduced range

Private Mobile Radio (PMR)

For more reliable, private communications, a commercial transceiver is recommended. As our mobiles use high-power transmitters and external antennas, communication between vehicles can generally be up to 5kms depending on terrain. Portable transceivers can also be used in this application.

A license is required for these transceivers which can be coordinated by Milpeak.

Advantages of PMR over UHF CB are:
• Privacy - the channel is not available on UHF CB transceivers and generally interference from the public does not occur on private channel
• Maximum power output for PMR transceivers is 25 Watts compared to 5 Watts on UHF CB

We sell several PMR solutions - please refer to the Simoco and Tetra pages in our Products section.

Duplex systems

Duplex systems require the use of a repeater base station to relay transmissions between users. The repeater is generally placed in a prominent location - either on a hill or using a high antenna mast. This gives all users the same range between users as the base station and increases the range of the system to up to 60kms depending on the repeater site location.

A duplex system is made up of two components - network infrastructure and terminals.

The basic premise of a duplex system is that the terminals (mobile and portable transceivers) operate on separate transmit and receive frequencies. A base station operates on the opposite frequencies such that all transmissions from a portable are received by a base station, and re-transmitted on the terminal’s receive frequency.

Network infrastructure

Network infrastructure for a single-site PMR system comprises of a base-station transceiver, building or enclosure, diplexer, power supply, antenna and mast.

The base station is the core component and is a much higher quality transceiver than a terminal. The transceiver is capable of duplex operation, i.e. it receives and transmits at the same time. It also has superior specifications compared to a terminal as its performance is often the limiting factor for the quality of the entire system. A base station is also often placed in a site where many other base station transceivers are co-located and hence must be of high quality to minimise interference between repeaters.

For single-site analogue applications, Milpeak recommends the TRB9200 transceiver. The base station has all the features required for not only single site systems but also for integration within larger multi-site systems.

Refer to the TRB9200 PDF brochure for more information .

For a single site where there are no other systems sharing the same site, a duplexer is employed to allow a single antenna to be used for both transmit and receive functions of the repeater. The duplexer chosen is a site specific driven decision due to engineering considerations such as the sharing of existing infrastructure. For sites with no other base stations housed, Milpeak uses RFI supplied duplexers such as outlined in this brochure.

The antenna is key to achieving the coverage requirements of the network. For sites where equal coverage is required in all directions, (e.g. a mine site where the repeater is mounted in the middle of the site), an omni-directional antenna is deployed. For coverage in particular directions, (e.g. along a haul road or a railway), directional antennas can be used to limit coverage and interference from areas not around the road, and to maximise the range along the road. We use and recommend RFI manufactured antennas such as these brochures on Collinear and Yagi antennas. .

Generally, a 12VDC supply is required for most PMR repeater transceivers. Where there is mains power, a simple power supply is employed to convert from mains power to 12VDC. It is good practise to use a power supply that includes a back up battery to allow the repeater to remain functional during mains power outages. For sites where mains power is not economical, solar and wind-generated supplies are used.

There are many choices available for housing repeaters, including;

• Existing radio sites - these can often be used on a rental basis if not owned by the client. Consideration is required in these instances to minimise interference, manage power supply usage, investigate possible sharing of antenna infrastructure and when antennas are being installed, outages of other systems must be coordinated.

• Stand-alone portable site - Milpeak and its sister company, Remcom Pty Ltd, provide a number of solutions ranging from light weight skid mount frames and trailers housing equipment, solar power, batteries and mast.

• Permanently-fixed equipment enclosure - a double-skinned metal enclosure is often used to house equipment and batteries at sites where a building is not warranted but the system is to be housed permanently. This is often used on haul roads and railways.

Engineering Considerations

The following points require consideration when designing and planning network infrastructure:

• Coverage analysis - masts and civil works associated with new base stations vastly out-weigh the costs of the radio equipment itself. Considerable savings can be found in the implementation costs of new radio base stations when good quality coverage analysis is performed during the design of a system. This enables the designed to specify only the hieght of mast required to achieve the requirements which leads to more efficient use of capital.

• Real Estate - If the site is not owned by the user's organisation, access to the site must be negotiated with the owner of the site.

• Power Supply Design - less of an issue with mains powered sites, but in solar powered sites, the design of the power supply is crucial in providing a robust system at the best price. Milpeak uses industry standard dimensioning tools and practises to dimension systems with the required availability at best price.

Terminals

The terminals used in duplex radio systems are the same as those used in simplex systems. The transceivers are programmed accordingly to use the split receive/transmit pair of frequencies used by the repeater and can also have simplex frequencies (often including UHF CB frequencies) programmed.

Depending on the functionality required, Milpeak recommends and stocks a large range of Simoco portables and mobile radios.