Installation Notes - Icom IC-PW2 Instruction Manual

INSTALLATION NOTES

For amateur base station installations it is
recommended that the forwards clearance in front of
the antenna array is calculated relative to the EIRP
(Effective Isotropic Radiated Power). The clearance
height below the antenna array can be determined in
most cases from the RF power at the antenna input
terminals.
As different exposure limits have been recommended
for different frequencies, a relative table shows a
guideline for installation considerations.
Below 30 MHz, the recommended limits are specified
in terms of V/m or A/m fields as they are likely to fall
within the near-field region. Similarly, the antennas
may be physically short in terms of electrical length
and that the installation will require some antenna
matching device which can create local, high intensity
magnetic fields. Analysis of such MF installations
is best considered in association with published
guidance notes such as the FCC OET Bulletin 65
Edition 97-01 and its annexes relative to amateur
transmitter installations.
The EC recommended limits are almost identical to
the FCC specified 'uncontrolled' limits and tables exist
that show pre-calculated safe distances for different
antenna types for different frequency bands. Further
information can be found at https://www.arrl.org/.
• Typical amateur radio installation
Exposure distance assumes that the predominant
radiation pattern is forwards and that radiation
vertically downwards is at unity gain (sidelobe
suppression is equal to main lobe gain). This is true
of almost every gain antenna today. Exposed persons
are assumed to be beneath the antenna array and
have a typical height of 1.8 m.
The figures assume the worst case emission of
constant carrier.
For the bands 10 MHz and higher the following power
density limits have been recommended:
10–144 MHz 2 W/sq m
EIRP clearance heights by frequency band:
1 Watts 2.1 m
10 Watts 2.8 m
25 Watts 3.4 m
100 Watts 5 m
1000 Watts 12 m
Forward clearance, EIRP by frequency band:
100 Watts 2 m
1000 Watts 6.5 m
10,000 Watts 20 m
100,000 Watts 65 m
In all cases any possible risk depends on the
transmitter being activated for long periods. (actual
recommendation limits are specified as an average
during 6 minutes) Normally the transmitter is not
active for long periods of time. Some radio licenses
will require that a timer circuit automatically cuts the
transmitter after 1–2 minutes etc.
Similarly some types of emission, i.e., SSB, CW, AM
etc. have a lower 'average' output power and the
assessed risk is even lower.
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