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Communication

Communication is becoming popular with off roader’s of all types because it is available in a variety of types, and enables groups of vehicles to maintain contact and to allow organisers of events to co ordinate with each other.

Many types of radio communications are available, so what are they, and what should we look for before purchasing such equipment. Radio equipment generally falls into two distinct categories, these are public radio systems or networks and amateur radio types, the public radios are simply that, frequencies designated for public use; amateur equipment requires tests and licensing.

Public Mobile Radio, or PMR is divided into two types, these are citizens band equipment which is available cheaply, and often requires a fixed installation into a vehicle, and hand held radios which are battery operated or rechargeable.

Citizens Band CB

Citizens band radios became popular in America and other countries, it became popular in the UK in the late 1970’s, but was the older illegal AM equipment often imported and used illegally here in the UK, and often tracked by the authorities. Being so popular meant that Government could not keep up with the problems created by such systems, they were everywhere; in vehicles as mobile units, and in homes and workplaces as base stations, and caused many problems with household equipment.

Considering the numerous problems, and the inability to constantly track offenders, particularly mobile users; Government decided to offer a legal alternative to the old amplitude modulation (AM) sets. Frequency Modulation (FM) was that alternative, it eliminated many of the problems with the older televisions and radios of the time, as well as having potential to make Governments money as these had to be licensed.
FM sets had considerably fewer channels than the American AM sets; these were increased over the years, but can still become congested if there is a high usage rate in a particular area.

CB units can be used in any vehicle with a 12 volt supply, these are simply connected to an appropriate power point; or used as a base station in the home with a battery replacing power supply, and an appropriate antenna. Vehicular use means they are built into the vehicle in much the same way modern radio/CD players are, or mounted in a convenient place for the driver to reach while on the move. Choices of CB units are immense; it is a simple decision of which features you require, and the price you are willing to pay for any particular unit.
CB’s require additional items to allow them to be installed and set up within a vehicle; these are an external antenna, coaxial cable of the correct sort, connection plugs for the coaxial cable, and an SWR meter to adjust the antenna impedance to the CB.

Antenna’s come in two basic types, these are mobile and base station, the base station antenna is mounted and permanently fixed to the home, then connected by coaxial cable to the CB.

Mobile antenna’s are a different matter, they come in a variety of specifications, sizes, styles, and mountings; the main types are the permanently mounted types which attach to the vehicle at a suitable point and are left. Antennas work by connecting to a ground plane, this is basically a large earth which is made up with the steel of a vehicles body, the body is drilled and the antenna mounted. As long as the earth side of the antenna mounting connects directly to clean steel on the vehicle it can be connected to the CB, its SWR checked, and the antenna trimmed to correct the SWR; the actual aerial will then transmit or receive a signal.

Other forms of antenna are the mag mount, these are a self contained unit mounted on a magnet which simply attaches to any metal surface of the vehicle, other types of semi permanent antenna are the gutter mount which attach to the gutter of older vehicles. Magnetic mounts are fine for limited applications, they do get knocked off easily, and it is not uncommon for them to fly off vehicles as they travel at higher road speeds. Gutter mounts allow the gutter mounting bracket to remain attached, but the antenna can be quickly and easily removed when required, this may be when the vehicle is parked to prevent vandalism or when entering low or restricted height accesses.

Permanently mounted antenna are the safest, and the most efficient in terms of transmission and reception, mounting requires care as the position of the mounting determines the position of the best transmission or reception of signals. However the ground plane of the vehicle body can influence this to a large degree, ideally the best mounting place is in the middle of the roof as it assures an omni directional signal transmission and reception.
Mounting an antenna at the rear of the roof on the vehicles centreline will ensure the best transmission and reception will be towards, and from the front of the vehicle as the bulk of the ground plane surface metal is in front of the antenna.

What are the pro’s and cons:

CB offers a reasonable range and allows you to chat with other CB users while travelling on road as well as communications off road.

CB can be a cheap and flexible way to communicate if you operate off road within varying, or differing groups of people, just ensure you are all on the same channel, it is a universal medium in the UK.

Off road usage may damage the antenna, often it is when operating in wooded areas, or areas overgrown where it can constantly hit the antenna and throw out the SWR if the antenna becomes damaged, this will damage the CB itself. In winter conditions the ice or freezing water will accumulate on the antenna, this can overload the mounting, or it can throw out the SWR and blow the CB.

Vehicular CB units are fixed, to use them you have to be in the vehicle, or standing next to it

CB operates on FM in the UK, it does limit its applications in many countries as it is illegal, many countries require its removal before entering their country.

CB can be prone to interference from a variety of sources, these are mainly large transmitters or overhead power cables.

PMR

PMR stands for Public Mobile Radio, the Government have allocated frequencies for use by low powered mobile transceivers (two way radio) these require no knowledge, licensing, or testing; simply purchase and use.

PMR sets are usually hand held units, this form of two way radio is becoming widespread within many industries for cheap and instant communications, they are used in a variety of applications ranging from security to crane operations. Such technologies have seen PMR units become affordable to many industries, these have embraced them, leading to even more being purchased and the obvious price drops; this means they are now affordable for home users.

PMR radios operate on eight main frequencies, these are sub divided into many channels or sub-frequencies, they have varying ranges of operation, the main ones are 3Km, 5Km, and 8Km operating ranges in ideal conditions. Some are basic battery operated units using dry batteries, others are rechargeable units with either rechargeable individual batteries, or rechargeable battery packs, most are packed with more features than CB, and are fully portable.
Many designs and styles are available with a considerable amount of features, there are outdoor units which are waterproof, and many different colours are available for the vain among us, there are hand held CB’s as well but these tend to be poor.

Basic PMR units operate from dry batteries and have very few features, they operate on the eight basic channels, so are of limited use. For off roading, as always get the most channels and longest operating ranges and time rechargeable units you can afford, you may find it beneficial to add a few accessories as well, these would include an in car charger for continual use.

Pro’s and Cons

PMR has a shorter range than a CB with an externally vehicular mounted antenna.

PMR battery life can vary, rechargeable units offer the option to purchase chargers designed purely for vehicular use.

PMR units are portable so they can be carried by members of a group leaving the vehicles, this is advantageous when scouting in front, or when guiding vehicles over tricky terrain; they are a great asset when winching under difficult circumstances.

PMR units are available in multiple units, a four pack is available for less than a CB when its antenna and coaxial cable are considered, meaning one multi pack of four rechargeable units will service four vehicles instead of one vehicle.

Small antenna’s are available for vehicular use, these are mainly magnetic or gutter mounted types, and can quickly be installed and left on a vehicle for greater operating ranges, yet quickly be detached and the portable antenna connected when leaving a vehicle.

No damage will occur from external antenna’s while off roading, many simply leave the standard antenna on the unit and use it as it is.

When awkward recoveries are attempted such as a snatch recovery of a stranded vehicle, the watcher can communicate with both vehicles, so safety is a significant issue when attempting such recoveries.

Legislation

Many people understand the laws regarding mobile communications equipment such as mobile phones while travelling in a motor vehicle, it is illegal to use them; many do not understand the laws regarding CB or PMR equipment.

PMR is exempt from these laws, it is perfectly legal to use both PMR two way radio, and CB equipment while driving, this exemption exists as emergency vehicles and operatives such as Police, fire, and ambulances have to use two way, or PMR radios. Should you be unlucky enough to be stopped by the Police you will need to show them the equipment to prove it is a PMR radio and not a mobile phone.

Operating Range

Operating ranges of both CB and PMR will be reduced significantly in built up areas such as towns or cities, or in hilly off road terrain, this must be considered when using both systems. Generally the PMR has the edge over CB systems in clarity as it uses more modern technologies in its construction, CB has a slight edge when used among large steel constructions, but for off road communication over the short ranges encountered, there is little difference.

My Opinion

It must be emphasised that this is purely my own opinion based upon using both systems.

My preferred choice is PMR, this is due to its extra flexibility over CB, both perform well for vehicular communication over short distances, but the portable nature of PMR units are more beneficial over a wider range of off roading applications. I personally have an eight pack of top range PMR radios, these are obviously rechargeable, and I have invested a little extra in the in car chargers, this means for our average group of four vehicles, we each have a spare unit.
Less fixed antenna damage with PMR swings it for me, and I have found the 8Km range is more than adequate for our requirements, and if we leave the vehicles any passengers can have a unit in the vehicle also.

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