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Power Density
From the radar equation, power density at the target is given by:
Pd = PT GT
4π r2
Where:
Pd = Power density in W/m2
PT = Transmitter output power in Watts
GT = Antenna gain as a multiple of input power
r = Range to target in metres
From the Rad24 radio specifications:
Power output is 1mW Peak
Chip antenna peak gain is 3dBi or 2 times the input power
Measurement range is 20cm or 0.2m
Pd = 1x10-3 X 2
12.568 X 0.22
Pd = 3.978x10-3 W/m2
Pd at 20cm range is 3.978mW/m2
Dividing this by 10,000 to express power density in W/cm2 gives:
397.8nW/cm2
This is the peak power density assuming the RF output is 1mW Continuous Wave; multiply this figure by the duty
cycle and the average power density is reduced proportionately. Further, this calculation uses the peak gain of
the chip antenna stated as 3dBi in the manufacturers data sheet, in practice this gain is rarely achieved being
nearer to 1 to 1.5dBi.
RF Exposure Limits
Power density at the Rad24 Antenna is well below the Whole Body Average SAR (Specific Absorption Rate) of
80mW/Kg exposure limit given at ANSI/IEEE C95.1-2005 and OET Bulletin 65 Edition 97-01 dated August 1997.
Under the terms of FCC CFR Title 47 Volume 1 Part 2.1091 and Part 2.1093 this equipment is categorically
excluded from routine environmental evaluation for RF exposure.
Article 3(1) of Directive 2004/40/EC of the European Parliament and of the Council dated 29 April 2004 (The
Physical Agents Directive) gives an Exposure limit for Whole Body Average SAR as 400mW/Kg. Rad24 Peak ERP is
not more than 4mW assuming a 6dB antenna.
Antenna Installation
Internal Chip Antenna
There must be no metal objects within 7mm of the antennas long edge and 20mm from the short edges. See
diagram below
87
Mantracourt Electronics Limited T24 Technical Manual
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