One of the first questions potential users of the GRouter4 Wifi router ask is, “What range can I get?” The easy answer is: it depends. Which is true, but not very informative. Wireless range depends on a lot of factors so it is difficult to predict with high accuracy what range a given application will achieve. With some forethought and understanding, however, it is straightforward to predict if range is likely to be a problem.
The range that a given setup can obtain is largely determined by the transmit power, receiver sensitivity, and the transmission path losses or gains due to connectors, cables, and antennas and obstructions. Other important external factors influencing range are antenna height, wireless noise, and interference.
The GR4 router is based on the Digi WiME module. The relevant specifications for the module are as follows:
- Frequency Band = 802.11b 2.4 GHz
- Data Rate = up to 11 Mbps
- Transmit Power = 16 dBm
- Receiver Sensitivity = -82 dBm at 11 Mbps, -92 dBm at 1 Mbps
Adept ships the GR4 WiFi with a 2 dbi Omni Directional whip antenna. Adept offers a 5 dbi antenna option for significantly improved range, for those applications that need it. Adept can also provide 15 dbi directional antennas to increase range even further.
One way to get an estimate of the range possible is with a range calculator that is based on a mathematical model of the setup. There are several of these available on the web. One good one is at Antenna System Designer. (You must request a free log in account to use the calculator.) The mathematical model provides a theoretical range or ball park figure. If the theoretical range for a given set up is less than the range required then its not likely to work. If the theoretical range is well in excess of that required then there is a reasonable chance it will work. For marginal applications close to the theoretical range, only field testing will tell for sure.
Adept performed some field testing to verify what sort of real world ranges were possible with these units. Since most applications are for outdoor, building-to-building connectivity, the tests were performed outdoors. The tests consisted of two units in ad hoc mode with three different antenna configurations. The units were tested with clean line of sight in relatively uncluttered environments. Range was measured using gps with an accuracy of +- 5 meters. One unit was mounted about five meters above ground, the other about two meters. Between 100 and 200 packets per second were sent across the WiFi connection. The results are as follows:
In the first test, each unit had a 2 dbi omni whip antenna. At a range of 243 meters there was no degradation in packet rate. At a range of 280 meters there was some degradation in packet rate (lost packets).
- In the next test, each unit had a 5 dbi omni whip antenna. At a range of 465 meters there was no degradation in packet rate. At a range of 736 meters there was some degradation in packet rate.
- In the last test, one unit had a 5 dbi omni whip antenna, the other unit had a 15 dbi directional antenna. At a range of 1242 meters there was no degradation in packet rate. It was not possible to get a clean line of sight for a longer range test to find the limiting range for this configuration.
- Indoors, the range is limited by walls and interference. A range of 50-300 feet is usually all one can expect with a 2 dbi antenna.