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Maintaining Compliance at 900 MHz (U.S.A. and Canada Only)
The following table outlines the minimum lengths of
Antenna Gain | AntennaGain | Minimum Feedline | Power Level |
(dBd) | (dBi) | Length (Loss in dB) | at Minimum Length |
Unity (0 dB) | 2.15 dBi | 3 meters (1.0 dB) | +31.15 dBi |
3 dBd | 5.15 dBi | 3 meters (1.0 dB) | +34.15 dBi |
5 dBd | 7.15 dBi | 3.1 meters (1.2 dB) | +35.95 dBi |
How Much Output Power Can Be Used?(U.S.A. and Canada, 900 MHz systems)
900 MHz transceivers are normally supplied from the factory set for +30 dBm (1 Watt) RF power output; this is the maximum transmitter output power allowed under FCC and Industry Canada rules. The power must be decreased from this level if the antenna system gain exceeds 6 dBi. The allowable level is dependent on the antenna gain, feedline loss, and the transmitter output power setting.
In regions where ETSI standards apply, the maximum allowable RF output is generally limited to 100 mW (+20 dBm) on 2400 MHz.
Calculating System Gain
To determine the maximum allowable power setting of the radio, perform the following steps:
1.Determine the antenna system gain by subtracting the feedline loss (in dB) from the antenna gain (in dBi). For example, if the antenna gain is 10 dBi, and the feedline loss is 2 dB, the antenna system gain is 8 dB.
2.Subtract the antenna system gain from 36 dBm (the maximum allowable EIRP). The result indicates the maximum transmitter power (in dBm) allowed under the rules. In the example above, this is 28 dBm.
3.If the maximum transmitter power allowed is less than 30 dBm, reduce the transmit power accordingly using the radio menu system (Main Menu>Radio Configuration>RF Output Power Setpoint), or introduce additional feedline loss. The EIRP of the antenna system should never exceed 36 dBi.
