Repeater Systems

The Problem

Simplex Radio Mode
Fig.1 - Simplex Radio Operation

Radios typically require line of sight to work correctly. Obstacles in that line of sight drastically reduces reception. The bigger or thicker the obstacle, the more it affects radio reception. The worst obstacles are lead lined buildings or roofs and solid rock, stone or concrete. Electro-magnetic waves simply cannot penetrate obstacles very well and every obstacle results in reduced reception.

Portable two way radios only typically broadcast at 4w on UHF and 5W on VHF.

The low power transmission combined with obstacles means that a large obstacle or several smaller obstacles will most likely inhibit the radio signal and stop the radio from successfully communicating with other radios.

See Fig.1 for an example of this.

The Solution

Simplex Radio Mode
Fig.2 - Radio Repeater (Half-Duplex) Operation

The solution to this problem is a simple one. Instead of the radios talking directly to one another, as per the Fig.1 diagram above, the radios all transmit to the "radio repeater mast" which in turn re-broadcasts the signal to the other radios.

Repeater antennas (masts) are usually mounted on the top of buildings and other high up places. And because every radio is within line of sight, there's no (or few) obstacles to block the signal.

As demonstrated in Fig.2, all radios can see the antenna and can communicate with it. And if there was one or two minor obstacles in the way, that would not be too much of a problem.

Fig.2 shows an antenna on a tower, but that's just for illustrative purposes. Typically an antenna on a 3-6m pole is placed on the highest point of a building, usually on the roof.

Nevertheless, as long as there aren't too many obstacles in the way, and the antenna is in a central position, most radios should be able to receive from, and transmit to, the repeater.