Base Stations improve calls to mobiles.

A common question we hear at Radphone is “How far will my two way radios go?”
Unfortunately, this is a little like the old “How long is a piece of string?” question.
A number of factors affect the range of two way radios. Transmit power, antenna efficiency, height above ground and surrounding terrain are some of the factors to take into account.
If a base station is used, range is improved by the external antenna on the roof of the building. The higher the antenna, the better the range. (See the caveat to this further down).

Unfortunately, a standard base station will only improve base to mobile calls. Mobile to mobile communication isn’t helped at all. For this we need a repeater.

Repeaters improve overall radio coverage.

Motorola-SLR5500

In two way radio systems, poor mobile to mobile range is a fairly common problem. This can be due to either large obstructions or simply distance between radios.

A repeater is a type of base station which can be used to improve the coverage of a radio system.
It works by receiving a radio signal on one frequency and simultaneously re-transmitting the signal on another frequency.

Repeaters are useful in extending radio range. If mobiles are too far apart to receive each other, a repeater located in the centre of the coverage area will effectively, hop or bounce the signal.

Repeaters also work well at overcoming “line of sight” limitations.

If mobiles are seperated by an obstruction such as a hill or large building, the radio signal can be blocked.
Installing a repeater at the top of the obstruction allows mobiles to “see” the repeater’s antenna… and communicate through the repeater. The height of the repeater also gives a bonus of increased range.

The higher the repeater antenna, the further we can transmit.

Beware though, the relationship between antenna height and transmit range is not straightforward.

Doubling antenna height doesn’t double the range. (It increases range by about 30%).

So, even quadrupling antenna height wouldn’t double the range.

Now, imagine the scenario of a repeater antenna at the top of a 100 meter building…

To double the height of the antenna (above normal ground level) a pole of 100 meters would need to be installed on top of a 100 meter building. This costly, nearly impossible task is just not be viable for a 30% improvement in range.

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