INSTALLATION NOTES
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For amateur base station installations it is recommended
that the forward 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 http://www.arrl.org/.
•
Typical amateur radio installation
Exposure distance assumes that the predominant radiation
pattern is forward 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 a constant
carrier.
For the bands 10 MHz and higher the following power
density limits have been recommended:
10–50 MHz 2 W/sq m
Vertical clearance by EIRP output
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 by EIRP output
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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List of Country codes (ISO 3166-1)
Country
Codes
Country
Codes
1 Austria
AT
18 Liechtenstein
LI
2 Belgium
BE
19 Lithuania
LT
3 Bulgaria
BG
20 Luxembourg
LU
4 Croatia
HR
21 Malta
MT
5 Czech Republic
CZ
22 Netherlands
NL
6 Cyprus
CY
23 Norway
NO
7 Denmark
DK
24 Poland
PL
8 Estonia
EE
25 Portugal
PT
9 Finland
FI
26 Romania
RO
10 France
FR
27 Slovakia
SK
11 Germany
DE
28 Slovenia
SI
12 Greece
GR
29 Spain
ES
13 Hungary
HU
30 Sweden
SE
14 Iceland
IS
31 Switzerland
CH
15 Ireland
IE
32 Turkey
TR
16 Italy
IT
33 United Kingdom
GB
17 Latvia
LV
