Andrew ION-B Series, User Manual

Page: 168 / 181

168 ION-B User Manual
This equation includes the following factors:
• G is the antenna gain (in dB) compared to isotropic radiating antennas;
• P is the RF power that is present at the antenna connector (in W);
• L is the total loss (in dB) between the TFAx remote unit output port and the antenna input
port;
• S is the maximum allowed power density in air (in W/m 2 ). Its values should be calculated
according to the limit exposures to time-variations and magnetic fi elds. The reference values
are reported in the ICNIRP guidelines, unless otherwise specifi ed by specifi c regulations.
(please note that, if regulations only defi ne the maximum electrical and magnetic fi eld strengths,
the allowed power density is able to be be obtained by:
S= E
2
/377= B
2
·377
where 377 is the characteristic’s impedance of the empty space).
Example 1.
A Medium Power TFAM 18/20P must distribute mobile signals through a directional
antenna, fed by a 2-metre length RG223 cable (no splitters used). The antenna gain is 7 dB and
the ION-B system distributes one GSM 1800 MHz carrier and one UMTS 2100 MHz carrier.
The maximum allowed power density we have to comply with is:
S = 10 W m -2
(typical ICNIRP reference level for general public exposure to time-varied electric and magnetic
fi elds).
By reading the relevant notes for the TFAM 18/20P remote unit, we know the overall output
power at the antenna port is able to be estimated as follows:
• 20 dBm ± 2 ( +22 dBm maximum, equivalent to 0.158 W) for the Cellular 850 MHz band
• 20 dBm ± 1.5 ( +21.5 dBm maximum, equivalent to 0.141 W) in the PCS 1900 MHz band.
• The total output power at the antenna port is therefore P = 0.158 + 0.141 = 0.299 W.
By reading the cable specs, we get that RG223 cable losses can be estimated at 0.55 dB/m.
Total losses between the TFAM 18/20P output port and the antenna input port can therefore be
estimated as follows:
L = 0.55 (dB/m) x 2 (m) = 1.1 dB
By replacing the above values of G, L, P, S parameters inside the formula 6.1, we therefore get
the the following minimum safety distance from the antenna:
r
min
= { 10 · exp [ (7 - 1.1) / 10 ] · 0.299} / (4·π·10) } · exp (1/2) = 0.096 m
Example 2.
A Low Power TFAH85/19 through a directional antenna is used, fed by a 20 -metre
length ½” cable, with a 2-way splitter. The antenna Gain is 7 dB and the ION-B system distributes
one Cellular 850 MHz carrier and one PCS 1900 MHz carrier.