Private Mobile Radio (PMR) or as it is sometimes called Professional Mobile Radio is widely used for businesses as a very convenient way of communicating. It typically refers to sophisticated radio trunking services that provide two-way mobile radio communications for mobile users to connect to PMR voice telephony and data networks. There are a wide variety of such systems, for example:
- personal radios used within a large factory, and perhaps interfaced to the telephone system
- radios fitted to fleets of vehicles such as taxis and delivery vans.
- hand-held radios used by a family exploring the countryside, sometimes called walkie-talkies, which typically use a short-range two-way radio protocol called PMR 446.
PMR offers a two-way communications service that permits users to talk over a short distance on a simple local system or wide-area, even nation-wide on a more complex system, without incurring any costs on the calls made – no matter how many or for how long.
Based in Barbados in the West Indies, Mobile & Marine Systems are one of the Caribbean’s leading professional private mobile radio communication solution suppliers and radio systems integrators, backed by more than 25 years of experience within the regions. We are authorised sales, support and service agents / dealers for Icom and for Tait Electronics. As radio systems integrators we operate throughout the Caribbean (Anguilla, Antigua, Aruba, Bahamas, Barbados, Cayman Islands, Cuba, Dominica, Dominican Republic, Grenada, Guadeloupe, Haiti, Jamaica, Martinique, Montserrat, Netherlands Antilles, Puerto Rico, St. Kitts & Nevis, St. Lucia, St. Vincent & the Grenadines, Trinidad & Tobago, Turks & Caicos, Virgin Islands plus Belize, Colombia, Costa Rica, French Guiana, Guatemala, Guyana, Honduras, Nicaragua, Panama, Suriname and Venezuela).
The following information is provided to give you some background information about Private Mobile Radio (PMR) and explain some of the terms and jargon you might find in product descriptions. Please Contact Mobile & Marine Systems – Barbados if you require more advice.
Background to Private Mobile Radio (PMR)
PMR is the oldest form of mobile communications – it has been in use for over 70 years. It is used by many taxi and courier firms, security guards and utility companies. Many rural businesses choose the PMR option, because they find that they simply do not have mobile phone coverage, or they are in an area where the network frequently goes down.
PMR is particularly well suited to operations requiring the passing of frequent short voice or data messages from a central point to individuals or groups of personnel.
Initially the PMR systems consisted of a base station with a number of mobile stations. Communication used a single frequency, with simplex push to talk transmissions. As pressure rose on the frequency allocations, often frequencies had to be shared. As the systems almost invariably used frequency modulation, squelch was employed so that the audio from the received was only switched on when a signal was present. Developments of this known as DTMF (dual tone multiple frequency) and CTCSS (continuous tone, coded squelch system) were used to enable only the required users to hear the call.
These systems were only able to communicate over relatively short distances. They used a single central base station to communicate with all the mobile stations. This considerably reduced their coverage area. To overcome this a system known as trunking was devised whereby several transmitters could be used and the signal was “trunked” to the correct station. Several systems are available for this but the one that has gained by far the widest use is specified as MPT 1327.
Mobile and portable radio is an effective solution to the communication needs of many businesses, factories, hospitals and service companies. The simplest radio systems consist of a number of hand portable radios communicating between each other. This services the most basic requirement for many users such as hotels, security, construction sites, warehouses and events organisers.
The real value of a radio solution comes from integrating the radios with the other communications services. An example is the interconnection of the radio systems with a company telephone system – enabling mobile personnel with hand portable radios to place and receive telephone calls.
Similarly office personnel on the telephone system can call mobile personnel whilst they move around the works site. Another example is providing desktop controllers with direct access to the radio network.
Office based personnel in regular contact with radio users can have their own radio controller providing facilities such as radio channel monitor, channel change and emergency call, as well as placing and receiving calls with radio users.
What determines the range of the radio?
The power of the radio is one of the main factors in determining range. Hand-portable radios are limited to 5 Watts ERP (radiated power from the aerial), whereas the power allowed from some mobile (vehicle-mounted) radios is 25 Watts ERP. Height is another important factor, as the higher the antenna, the further the radio waves can travel unobstructed.
Under ideal conditions, a PMR radio signal may be received up to 3km away; a professional hand-held up to 5km; and a vehicle-mounted up to several tens of kilometres. With the addition of a repeater system, the coverage can be extended to an entire country!
Frequency: VHF or UHF?
Typically PMR users are licensed for VHF (Very High Frequency, normally 133MHz-170MHz) or UHF (Ultra High Frequency, normally 430MHz-470MHz). Generally speaking, the lower the frequency, the greater the range of transmission. This does not mean that VHF is automatically the best choice, because VHF signals do not penetrate buildings as well as UHF, which is therefore more suited to urban areas.
Choosing between UHF and VHF for your system can be very difficult and even the experts get it wrong sometimes. We can help you make a choice and if necessary visit you to try out both systems before you buy.
Avoiding interference: CTCSS/DCS tones
To avoid radio users hearing messages that are not intended for them, the Radio Communications Agency will allocate specific frequencies to a business when it issues a licence. In addition to this, a system of sub-audible tones can be used to further restrict reception of messages.
CTCSS (Continuous Tone Coded Squelch System) is a fairly standard feature on all radios, but may be called something different by each manufacturer, e.g. Motorola call it Private Line, Kenwood call it Quiet Tone, etc. (DCS is the digital equivalent – Digital Code Squelch.) The CTCSS tone is carried, along with your voice, by the radio signal. The receiving radio is tuned to the same radio frequency as the transmitter, but will only “unmute” its speaker, allowing the message to be heard, if it can detect that the appropriate tone is present.
Typically there are 38 tones to choose from which means on a single frequency (eg 462.625Mhz) there could be up to 38 different users or user groups, each assigned to a different tone. Each group is able to have private conversations without the other groups being able to hear what they are saying. However, if any one group is having a conversation, no other group can transmit at the same time without blocking the signal because no matter which CTCSS tone they use, they are still using the same radio frequency.
On some licence-exempt PMR radios the tones are user selectable, giving effectively 38 individual channels on each radio frequency. PMR446 radios operate on 8 frequencies which are programmed into the radio when it leaves the factory. With 38 tones per frequency, you have up to 304 different combinations to eliminate interference.
Selective calling (SELCALLl) is the closest thing to privacy on radio. Normally a system enables single users to call other single users, on the same system, without any other users hearing what is being said.
With SELCALL individual units can be called from the Base. The called device will ring notifying the user that he is required. This is particularly useful where the driver is constantly out of the cab. When he returns a ring tone, or a flashing light, will indicate that the base was trying to make contact. The device can also be used to call the base. The display on the base will indicate the number of the device calling.
You can also define groups and sub-groups and program calls accordingly. Supervisors may have the functionality to call every user individually whereas the shop-floor staff may only have a group call facility.
It works in a similar way to CTCSS but uses 5 tones, sent when the transmit button is pressed, instead of a single continuous tone. The receiving radio is constantly looking for a signal on its frequency. When it sees that signal it checks to see if the CTCSS tone is present and correct, and then if programmed correctly checks to see if its 5 tone id is transmitted before it “unmutes”.
5-tone is normally used if the radio operators require extra privacy or if the over-all radio system is quite large encompassing different departments within a company. Each user can have his own ID and can be called if the radio has the correct features. These features may be used either from a contact list or a numeric keypad.
SELCALL systems are well-established with plenty of scope: most have a group call function to enable users to call all other users simultaneously, some utilise in-built timers to operate a lone-worker facility. You can call sub-groups, send status messages, use auto acknowledgement from the called radio, the list of features is endless. We can talk you through the details if you like the sound of a more private radio system.
Working with the telephone system: DTMF
DTMF (Dual Tone Multi Frequency) provides the tones you hear when you press a button on most telephones. It is the telephone equivalent of 5-tone signalling. In some organisations radios are required to work alongside and with the telephone system. It is quite simple to integrate a phone patch to a radio system, so that office workers are able to make internal telephone calls to workers who carry radios, and the workers can call the internal phones.
Most radios can receive DTMF to some extent and some can make pre-programmed calls, but only if you have a full numeric keypad can you really take full advantage of this system.
MPT 1327 Trunked Networks
A Trunked System is nothing other than the sharing of a pool of communication channels between many groups of users with each user having the exclusive use of a channel for the duration of their call. Conversations are kept between the two parties and not broadcast over the entire fleet.
Trunking is considered much more spectrally efficient because switching between multiple radio channels allows less blocking and provides service to more radios per channel. Consider that on a 20-channel conventional system, roughly 700-1,000 users can be served. In contrast, those 20 channels on a trunked, dispatch-type system can service between 2,000 and 2,500 users!
Some of the advantages of a trunked system are as follows:
- private one-to-one voice calls
- your fleet can be divided into different groups
- call diversion (call forwarding)
- status message call (a predetermined data message)
- calls from each device can be limited to calling preselected devices
- if an incoming device call is not answered the name of the calling party will be displayed so that the call can be returned
- text messages can be sent over the network using the data terminal.
Commercial Trunked Radio
The term “commercial trunked radio” was created by the International Mobile Telecommunications Association (IMTA) in an attempt to create a universal definition encompassingthe many names for the industry and to identify a specific kind of service. For example, commercial trunked radio is known as Specialized Mobile Radio (“SMR”) in the United States and is typically referred to as Trunked Radio Systems (“TRS”) in Asia and Public Access Mobile Radio (“PAMR”) in Europe.
Commercial trunked radio systems generally provide one-to-many and many-to-one mobile wireless voice communications services, often called mobile dispatch services. Although commercial trunked radio systems are traditionally characterised by this ability to offer one-to-many and many-to-one voice communications, today they offer much more, including data capacity and full access to the PSTN. Many systems also offer integrated services such as voice mail, data messages, faxes or data transfer.
Typical users include:
Electrical Suppliers and Distributors, Gas and Water Distributors, Bus Companies, Airport Authorities, Railways, Courier Services, Emergency Services, Construction Companies, Trucking and Fleet Management Companies, Hotels, Agriculture Industry, Health Services, Dispatch Companies, Taxi and Limousine Companies, Manufacturing Industry, Petroleum Industry, Service Technicians, Insurance Agents and Adjusters, Government Agencies, Real Estate, Security Services, Plumbing & Electrical Contractors, Concrete and Asphalt Companies.
APCO P25 radio systems
P25 stands for Project 25. Project 25 is the Project Name / Number, given to the joint development project to develop a public safety digital land mobile radio (LMR) standard. It is a joint project between the US federal government, the US Association of Public Safety Communications Officials (APCO) and the International Telecommunications Industry Association (TIA). Project 25 has been accepted as a national standard in the US and is designated TIA-102.
APCO P25 radio systems use what is called the Common Air Interface (CAI). This standard specifies the type and content of signals transmitted by compliant radios. One radio using CAI should be able to communicate with any other CAI radio, regardless of manufacturer.
Mobile & Marine Systems and PMR
Mobile & Marine Systems provide a comprehensive range of professional private mobile radio (pmr) and radio systems integration services for adding value to your portable communication needs. If you have questions, simply need more information, or, need to discuss specific requirements, please click on the Contact MMS button to e-mail us.