MPE

FCC ID: XAYWHD310V2

RF Exposure Info

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FCCID_1819455

EUT: WZRDnet Report No: 0048-120702-01
Model: WHD-310(V)2 FCC ID: XAYWHD310V2 & IC:9521A-WHD310V2

7.3. SAR & MAXIMUM PERMISSIBLE EXPOSURE

For portable devices (47 CFR §2.1093), RF evaluation must be based on specific absorption rate
(SAR) limits. Human exposure to RF emissions from mobile devices (47 CFR §2.1091) can be
evaluated with respect to Maximum Permissible Exposure (MPE) limits for field strength or power
density or with respect to SAR limits, whichever is most appropriate.

The EUT, WHD-310(V)2 is a portable product, SAR is required not MPE. However, since the
power is 76.6 mWatts x 0.197 < 60/f(in GHz). The SAR is exempted per FCC and IC
requirements.

Page 18 of 65
Advanced Compliance Laboratory, Inc. 6 Randolph Way, Hillsborough, NJ 08844, tel:(908) 927 9288

EUT: WZRDnet Report No: 0048-120702-01
Model: WHD-310(V)2 FCC ID: XAYWHD310V2 & IC:9521A-WHD310V2

CALCULATIONS

Given
E = (30 * P * G) / d
and
S = E ^ 2 / 3770
where
E = Field Strength in Volts/meter
P = Power in Watts
G = Numeric antenna gain
d = Distance in meters
S = Power Density in milliwatts/square centimeter

Combining equations and rearranging the terms to express the distance as a function of the remaining
variables yields:
d = ((30 * P * G) / (3770 * S))

Changing to units of Power to mW and Distance to cm, using: P
(mW) = P (W) / 1000 and
d (cm) =100 * d (m)
yields
d = 100 * ((30 * (P / 1000) * G) / (3770 * S))
d = 0.282 * (P * G / S)
where
d = distance in cm
P = Power in mW
G = Numeric antenna gain
S = Power Density in mW/cm^2

Substituting the logarithmic form of power and gain using: P
(mW) = 10 ^ (P (dBm) / 10) and
G (numeric) = 10 ^ (G (dBi) / 10)
yields
d = 0.282 * 10 ^ ((P + G) / 20) / S Equation (1)
S = 0.0795 * 10 ^ ((P + G)/10)/ d^2 Equation (2)
where
d = MPE distance in cm
P = Power in dBm
G = Antenna Gain in dBi
S = Power Density Limit in mW/cm^2

Page 20 of 65
Advanced Compliance Laboratory, Inc. 6 Randolph Way, Hillsborough, NJ 08844, tel:(908) 927 9288

EUT: WZRDnet Report No: 0048-120702-01
Model: WHD-310(V)2 FCC ID: XAYWHD310V2 & IC:9521A-WHD310V2

Equation (1) and the measured peak power is used to calculate the MPE distance.
Equation (2) and the measured peak power is used to calculate the Power density.

LIMITS

From §1.1310 Table 1 (B),
for Public S = 1.0 mW/cm2
for Professional, S = 5.0 mW/cm2

RESULTS

No non-compliance noted:

For this EUT, Max. P (pk)= 18.84 dBm, Max G= 2.0 dBi, and d=20cm

Plug all three items into equation (2), and yields,

Power Density Output Antenna Power
Limit Power Gain Density
(mW/cm2) (dBm) (dBi) (mW/cm2)
1.0/5.0 18.84 2.0 0.02

NOTE: For mobile or fixed location transmitters, the minimum separation distance is 20 cm, even if
calculations indicate that the MPE distance would be less.

Page 21 of 65
Advanced Compliance Laboratory, Inc. 6 Randolph Way, Hillsborough, NJ 08844, tel:(908) 927 9288

Document Created: 2012-10-06 11:26:57
Document Modified: 2012-10-06 11:26:57

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