One of the first questions potential users of the GR4 Wifi router ask is, “What range can I get?”
The easy answer is, “It depends.”
While it’s true, it’s 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 whether range is likely to present 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, antennas, and obstructions. Other important external factors influencing range are antenna: height, wireless noise, and interference.
The GR4 852 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 = 39.8 mW
- 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. For an extra charge, Adept can also provide higher dbi antennas to increase range.
One way to get an estimate of the possible range 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 Connect802. (You have to 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, it’s 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 give a reliable answer.
Adept performed some field tests to verify what sort of real world ranges were possible with these units. Since most applications are for outdoor, building to building, connections, the tests were performed outdoors. The tests consisted of two units in ad hoc mode with 3 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 5 meters above ground, the other about 2 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.
To say the least we were pleasantly surprised by the range we could get with just the standard 2 dbi antennas.
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.