GE GFK-2489 user manual Calculating System Gain

6

For convenience, the table below lists several antenna system gains and shows the maximum allowable power setting of the radio. Note that a gain of 6 dB or less entitles you to operate the radio at full power output 30 dBm (1 Watt).

Antenna System Gain	Maximum Power
(Antenna Gain in dBi*	Setting	EIRP minus
Feedline Loss in dB†)	(in dBm)	(in dBm)
6 (or less)	30	36
8	28	36
10	26	36
12	24	36
14	22	36
16	20	36

*Most antenna manufacturers rate antenna gain in dBd in their literature. To convert to dBi, add 2.15 dB.

† Feedline loss varies by cable type and length, as shown previously.

How Much Output Power Can Be Used? (U.S.A. and Canada, 2400 MHz systems)

Non-ETSI 2400 MHz transceivers are normally supplied from the factory set for +27 dBm (0.5 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 0 dBi. The allowable level depends on the antenna gain, feed-line loss, and the transmitter output power setting. In regions where ETSI requirements apply, the maximum allowable RF output is generally limited to 100 mW (+20 dBm) on 2400 MHz. License-free operation on 900 MHz is not permitted.

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 27 dBm (the maximum allowable EIRP). The result indicates the maximum transmitter power (in dBm) allowed under the rules. In the example above, this is 19 dBm.

3.If the maximum transmitter power allowed is less than 27 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 27 dBi.

GFK-2489 Chapter 6 Installation 6-11