Two Way Radios, How Far Do They Work?

A very common question we hear regarding 2 way radios is "How far will they work?" Unfortunately, this is a little like the old "how long is a piece of string?" question. A large number of factors affect the range of two way radios.

Transmit power, antenna efficiency, user height above ground and surrounding terrain are just some of these factors to take into account. The only practical comparison which we can make is in a mythical "ideal" situation, flat ground with no obstructions. As the most popular 2 way radio systems are the simplex, hand portable type, we'll discuss them first.

A good general guide is to expect a portable radio with 1 Watt transmit power on the flat (no obstructions) to provide around 1 mile of coverage. Doubling the transmitter power increases the range by about 1/3, so... At 2 watts we should get about 1.3 miles. At 4 watts the range may be around 1.7 miles.

As can be seen above, the link between transmit power and range is not as we might expect. We have to quadruple transmit power to gain less than twice the range! Note that here in the UK, portables are generally restricted to 5 Watts.

Although, it restricts the use of the radio somewhat, mobile radios permanently installed into vehicles will perform better. As the general restriction in the UK is 25 watts for mobiles, we end up with around 3 to 4 miles range, dependent on the antenna. Again, this assumes a simplex system, talking directly from one mobile to another.

If a base station is used within the system, it's range is improved by the installation of an external antenna on the roof of the building. The higher the antenna, the better the range. Again, the rule of thumb is very similar to the above... doubling the antenna height does not double the range! The range between mobiles is not affected unless the base station is a "repeater type" which enables mobile transmissions to "hop" between users. We get asked the same question time and time again. "How can I increase my range?"

As shown above, a LARGE increase in antenna height is needed (big cost implications). Or, a LARGE increase in transmit power. Here in the UK, OFCOM are the licensing authority and are unlikely to authorise this. Due to the lack of available frequencies, they tend to restrict coverage of radio systems to allow re-use of frequencies in adjacent geographical areas.