May 2001
Change to I.WiLL 300-24 Access Point Manual
Please replace pages 19—20 of the I.WiLL 300-24 Access Point manual (Version 1.1 - 02/00) with the
attached replacement page. Information about EIRP has been clarified and corrected on the replacement
page.
MAY 2001
1
Calculating the Link Budget
Calculating EIRP (Effective Isotropic Radiated Power)
Unlike the Tx output
power of the
devices, EIRP is
subject to both
antenna gain and
cable losses.
EIRP is the power radiating from an antenna taking into account the output power from
the transmitter, the connector and cable losses, and the antenna gain. Because many
antennas can provide a directional gain, the effective radiated power can increase. Losses,
such as cable losses can subtract from this amount. You calculate the EIRP as follows:
Formula: EIRP = Tx Power (dBm) - Cable Losses (dBm) - Connector Losses
(dBm) + Antenna Gain (dB)
Note: The FCC regulatory body has set the peak EIRP limit to 400 mW for
multipoint and fixed point-to-point applications per FCC 01-158 with
a peak power output of 100 mW. Only the antenna with which the
equipment is authorized may be used per FCC 47 CFR 15.204(c).
Industry Canada RSS-139, Annex B specifies the maximum
transmitter output at +30dBm, with a maximum EIRP (Equivalent
Isotropically Radiated Power) at +36dBm for multi-point
configurations and a maximum EIRP of +53dBm only for licensed
point-to-point applications.
In accordance with ETS 300-328 for 2.4GHz RLANs, the maximum
EIRP shall not exceed +20dBm, with a maximum SPD (Spectral
Power Density) not exceeding +10dBm/MHz. Confirmation is
required with the relevant European national radio communications
local authority for deviations from this specification.
Note: All EIRP work must be completed by a professional installer.
Working with Antenna Gain
To ensure the best range and interference suppression, the external antenna should be
directional, focusing the radio energy in one direction (toward the other end of the link).
The direction can be azmuthal or a horizontal radiation angle. A directional antenna
focuses the RF energy to the intended station rather than omni-directionally. This reduces
interference from other systems that are operating at the same frequency.
Note: In some situations, you may want to use an omni-directional antenna in your
system design. For example, you would use an omni-directional antenna for a base station
with remote sites situated in a 360… path around it.
When you select an antenna, pay particular attention to the gain specification. When you
select an antenna for a remote station, select an antenna with a gain that provides at least
13dB Fade Margin.
Antenna gain is specified in either dBi or dBd. When an antenna is specified in dBd, add
2.14dB to the value to convert it to dBi.
Note: All antenna gain work must be completed by a professional installer.
Version 1.1 - 05/01 19
)
Determining the RF Link
Calculating Propagation Loss
The propagation loss is the attenuation (reduction) in RF signal energy as it travels
through space. In most wireless systems, losses through space are the major contributor to
signal attenuation. When you know the intended installation locations of the base and
remote stations, determine the physical line of sight distance and then calculate the RF
attenuation as follows:
Formula: Attenuation (dB) = 100dB + 20log(d
where:
d
= Distance in Kilometers
km
100dB = Pathloss Constant
Note: The FCC regulatory body has set the peak EIRP limit to 400 mW for
multipoint and fixed point-to-point applications per FCC 01-158 with
a peak power output of 100 mW. Only the antenna with which the
equipment is authorized may be used per FCC 47 CFR 15.204(c).
Industry Canada RSS-139, Annex B specifies the maximum
transmitter output at +30dBm, with a maximum EIRP (Equivalent
Isotropically Radiated Power) at +36dBm for multi-point
configurations and a maximum EIRP of +53dBm only for licensed
point-to-point applications.
Industry Canada RSS-139, Annex B specifies the maximum
transmitter output at +30dBm, with a maximum EIRP (Equivalent
Isotropically Radiated Power) at +36dBm for multi-point
configurations and a maximum EIRP of +53dBm only for licensed
point-to-point applications.
In accordance with ETS 300-328 for 2.4GHz RLANs, the maximum
EIRP shall not exceed +20dBm, with a maximum SPD (Spectral
Power Density) not exceeding +10dBm/MHz. Confirmation is
required with the relevant European national radiocommunications
local authority for deviations from this specification.
km
Note: All propagation loss work must be completed by a professional installer.
Working with the Fresnel Zone
It is essential to locate your antennas at maximum above-ground height to ensure the most
effective and reliable link. Achieving maximum above-ground antenna height means that:
¥ all ground-based obstructions are cleared from the line-of-sight path
¥ the Fresnel Zone is clear of obstructions
20 Version 1.1 - 05/01
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