Andrew ION-B Series - Page 169

169MN024-010
The maximum allowed power density we have to comply with is:
S = 50 W·m
2
(typical ICNIRP reference level for occupational exposure to time-varied electric and magnetic
fi elds)
By reading the ION-B notes, we know that the output power per carrier at the TFAM antenna
port is
• 30 dBm ± 2 ( +32 dBm maximum, equivalent to 1.202 W) for the Cellular 850 MHz band
• 30 dBm ± 2 ( +32 dBm maximum, equivalent to 1.202 W) for the PCS 1900 MHz band
The ½” cable losses are 0.07 dB/m in the 900 MHz band, and 0.11 dB/m in the 2100 MHz band.
The splitter insertion losses are 3.5 dB. The total losses between the TFAH85/19 output port and
the antenna input ports can therefore be estimated as follows:
L
850MHz
= 0.07 (dB/m) x 20 (m) + 3.5 = 4.9 dB for Cellular 850 MHz signals
L
1900MHz
= 0.10 (dB/m) x 20 (m) + 3.5 = 5.5 dB for PCS 1900 MHz signals
The term “10 exp (G-L/10) P” which appears inside the formula 6.1 should therefore be
calculated seperately for each frequency, and then added in order to calculate the
composite contribution:
P
850MHz, ant
= 10 exp [(7-4.9)/10]· 1.202 = 1.949 W
P
1900MHz, ant
= 10 exp [(7-5.5)/10]· 1.202 = 1.698 W
P
composite
= P
850MHz, ant
+ P
1900MHz,ant
= 3.647 W
By dividing the total power through (4·π·S) and taking the square root according to the formula
6.1, we therefore get the the following minimum safety distances from the antenna:
r
min
= { P
composite
/(4·π·50)} · exp (1/2) = 0.02 m
Example 3. There is a Medium Power TFAM91/18/20 which is connected to an omnidirectional
antenna through a 10-metre length RG223 cable (no splitters used). The antenna Gain is 7 dB
and the ION-B system distributes two GSM900 carriers, two GSM1800carriers, and one UMTS2100
carrier.
The maximum allowed electrical fi eld strength is:
E = 6 V m
(typical Italian reference level for exposure to time-varied electric and magnetic fi elds). The
corresponding value of the maximum allowed power density is:
S = E
2
/377 = 0.1 W/m
2
By reading the relevant notes for the TFAM 91/18/20 remote unit, the overall output power at
the TFAM antenna port can be estimated as follows:
• 20 dBm ± 2 ( +22 dBm maximum, equivalent to 0.158 W) for the Cellular 910 MHz:
• 21 dBm ± 2 ( +23 dBm maximum, equivalent to 0.200 W) for the GSM1800)