User's Manual

Trailblazer Installation and User Manual version 1.02 27
4.2.2 Calculating the EIRP of an External Antenna
The for all bands of frequency the output of the Trailblazer TB series radio is
calibrated at the factory to limit the peak power output to +17dBm.
Using this example one can calculate the following:
Note that the radio is calibrated for a maximum output power of +17dBm.
Subtract the interconnecting cable and lightning protection losses of 2dB = total
power arriving to antenna of 15dBm. Now add the 2.4 GHz panel antenna gain
of 18dBi and this will give the total Effective Isotropic Rated Power of 33dBm.
For 2.4 GHz, the FCC uses a “3 for 1” rule. The “3 for 1” FCC rule states that for
every 3dB above 6dB of antenna gain you must lower the maximum RF power
available to the antenna from +30dBm ( 1 watt) by 1dB. In this example the
antenna gain is (18 – 6) 12dBi above 6 or (12 / 3) or 4 times 3dB above 6dB.
Checking to see if the transmit power meets the rule is done by subtracting 4
from +30dB equaling +26dBm. This transmitter output RF power is set to
+17dBm so it is below the limit.
For 5.8 GHz, the FCC allows a maximum EIRP of 50dBm. This would mean that
an antenna with a gain of 33dBi would be acceptable with no cable losses.
For 4.9 GHz, the FCC allows a maximum EIRP of 42dBm. If you had no losses in
between the radio and were using the supplied 22 dBi gain panel antenna you
would have an ERP of 39dBm which is under the maximum of 42.
Following this guideline ensures compliance with the maximum transmitter ERP
allowed with the antenna provided as a system.
4.2.3 RF Safety Hazard Warning
Due to the substantial energy radiated from these antennas, it is imperative that
they never be mounted such that the antenna or the cabinet containing the
antenna will be closer than 2 Meters (6.7 Feet) to any persons.