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Introduction Two-way radios can be a convenient, cost-effective means of keeping in touch with members of your family - children, in particular - during outdoor pursuits, skiing, shopping trips, etc., or work colleagues, if you work in an area that is geographically large, such as an airport, school or large retail outlet. Two-way radios are typically one of two types, FRS - Family Radio Service - which requires no licence, or GMRS - General Mobile Radio Service - which do. The principle difference between the two services is that a licensed GMRS two-way radio can, theoretically at least, have a maximum power output of 50 watts - practically, however, between 1 watt and 5 watts total power output is more typical - whereas an FRS two-way radio is limited to a maximum output of ½ watt (and cannot be modified to increase power output). This means that a typical GMRS two-way radio may have a range of up to 5 miles, whereas a typical FRS twoway radio is only effective over roughly half that distance. Two-Way Radio Range Unsurprisingly, the more powerful a radio signal, the further the signal can travel through the air and the greater the range of the transmitter originating the signal. In other words, the range of a radio transmitter is directly proportional to its power, or wattage; a commercial radio station, for example, may broadcast at anything up to 50,000 watts, while a mobile, or base station, two-way radio may transmit at anything up to 100 watts and a handheld two-way radio is typically limited to single figures in terms of wattage. When evaluating the output power and potential range of two-way radios, however, it is important to understand the difference between peak, and constant, power output. Radio manufacturers are, understandably, keen to quote peak power output - because it is always the larger of the two possible figures - but remember that this is a theoretical, instantaneous measurement of output power under ideal conditions. It is unlikely that ideal, laboratory conditions can ever be reproduced in the real world, so constant power output is, by far, the more reliable guide to how you can expect a two-way radio to operate; a two-radio capable of a constant power output of, say, 1 watt, may actually perform better than one capable of a peak power output of 5 watts, for example. Peak power output does also not take into account, of course, intervening physical obstructions such as buildings, trees, or hills - between two-way radio handsets and these can profoundly influence the effective range of two-way radio communication. As a rule of thumb, over a flat, unobstructed landscape, a typical two-way radio transmitting at an output of 1 watt can be received, clearly, up to 1 mile away. Doubling the output power typically increases the range by roughly 33% - further increases can be gained by increasing the antennae height - but,
conversely, the presence of anything that can block a radio signal may reduce the range. Two-Way Radio Channel Frequency The technology employed in a two-way radio is very similar to that employed by standard AM, or FM, radios. The major difference, of course, is that a two-way radio allows you to speak, as well as listen; in other words, a two-way radio transmits, as well was receives, radio signals. A radio transmitter relies on alternating current that fluctuates, or oscillates, back and forth very rapidly up to 1,000,000 times per second - for the creation of radio waves, and it is the rate, or frequency, of the oscillation that determines the frequency of the radio waves, themselves. Every commercial radio station broadcasts on a specific frequency, or frequencies - measured in kilohertz (KHz) or megahertz (MHz) - and it is a similar story for two-way radios. Commercial twoway radios can typically broadcast on between 6 and 14 frequencies, or channels, in the VHF Very High Frequency - or UHF - Ultra High Frequency - bands. Essentially, VHF transmissions tend to have a longer range than UHF transmissions, all other things - output power, antenna size, etc. - being equal, while UHF transmissions have more penetrating power, and are more easily received inside buildings, dense forests, etc. The ability to change channel frequency is important insofar as it allows one pair, or group, of twoway radio users to carry on a conversation without interference from other users in the vicinity, and vice versa. Some two-way radios are supplied with privacy, or squelch, codes, which allow a twoway radio to receive only transmissions specifically intended for it, while rejecting all other transmissions, including those on the same channel frequency.
Mark R Taylor is a UK national with an interest in gadgets. Read more of his articles at Gadget Heaven.
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