RF Exposure MPE calculation

FCC ID: N7N-MC5728

RF Exposure Info

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FCCID_1374683

RF exposure calculations for Sierra Wireless EV-DO MINI-PCI Express card
CDMA when its antennas collocated with Qcom 802.11 b/g/n card antennas inside
Ambient X-4000-xxx-xx smart grid node according FCC 47 CFR 1.307(b)(1).

The following RF exposure calculation made for EV-DO card, model: MC5728 (Sierra
Wireless Inc., FCC ID: N7N-MC5728) when his antenna collocated with antennas from
802.11 b/g/n card, model: Q802MKN ( Qcom Technology Inc., FCC ID: RUJ-
Q802MKN).

Both devices are embedded into the Ambient X-4000-xxx-xx smart grid node and has been
evaluated and complied with FCC RF exposure requirements separately, however in case
of X- 4000-xxx-xx, these antennas are collocated less then 20 cm from each other and
therefore cumulative RF exposure evaluation is required.

This device will be only used with a separation of 20 cm or greater between the antennas
and the user or nearby person. Device will be deployed in the fixed locations only but for
purpose of this calculation will be consider as a mobile transmitter per 47 CFR 2.1091(b),
and therefore has to comply with Maximum Permissible Exposure (MPE) limits.

EV-DO transmitter (FCC ID: N7N-MC5728) operates under Part 24E and 22H of FCC
Rules in cellular and PCS bands and has the transmitting characteristics which are
showing in Table1.
Table1
Maximum Peak Antenna
FCC Numeric Peak
Frequency Range output Duty Gain for
Part calculation MPE
Antenna Gain for
(MHz) power Cycle calculation MPE
No. (dBi)
(mW)
24E 1851.25 - 1908.8 814.7 100% 4.9 3.0903
22H 824.7 - 848.31 959.4 100% 2.2 1.6596

a) 802.11 b/g/n transmitter (FCC ID: RUJ-Q802MKN) operates under Part 15C of
,

FCC Rules in ISM band and has transmitting characteristics which are showing in
Table2
Table2
Maximum Peak Antenna Numeric Peak
FCC Frequency
output Duty Gain for Antenna Gain
Part Modulation Range calculation MPE for calculation
power Cycle
No. (MHz) (dBi) MPE
(mW)
802.11b/g/n 2412.0 -
15C 352.0 100% 3.6 2.2909
2462.0
, , ,

,

According 47 CFR 1.1310 FCC MPE limits for General population/Uncontrolled
Exposure are showing in the Table3
Table3
Magnetic
Electric Field
Frequency Field Power density Averaging
Strength [E]
Range (MHz) Strength [S] (mW/cm²) time (min)
(V/m)
[H](A/m)
0.3 - 1.34 614 1.63 (100)* 30

1.34 - 30 824/f 2.19/f (180/f²)* 30

30 - 300 27.5 0.073 0.2 30

300 - 1500 ------- ------- f/1500 30

1500 -100,000 ------- ------- 1 30
f = frequency in MHz
* = Plane-wave equivalent Power Density

Based on FCC Bulletin OET 65, the MPE calculations in case of multiple transmitters
have been e performed on the following and assumptions and equations:
1. For transmitters which operate in the frequency band with a same MPE limit
the Power Densities are summed. The Total Power Density shall not exceed
the Limit for this band
2. For transmitters which operate in frequency bands with a different MPE the
Power Densities are calculated separately for each band, and then divided by
Limit for each band. The sum of these ratios shall not exceed 1.
3. The calculation of the Power Density based on equation given in OET 65:

E = √ (30 x P x DC x G) / d (Eq.1)
and
S = E² / 3770 (Eq.2)

Where:
E = field strength in volts/meter
P = power in watts
DC = numeric duty cycle
G = numeric antenna gain
d = distance in meters
S = power density in milliwatts / square centimeter

Combining (Eq.1) and (Eq.2), S may be calculated as:

S = (30 x P x DC x G) / (3770 x d²) (Eq.3)

By changing units for P to mW and distance to cm, (Eq.3) can be written as:

S = [30 x (0.001 x P) x DC x G] / [3770 x (0.01 x d)²] (Eq.4)
Or:
S = (0.0795756 x P x DC x G) / d² (Eq.4)

Where:

P = power in mW
DC = numeric duty cycle
G = numeric antenna gain
d = distance in cm
S = power density in mW/cm²

4. According Table3, limit for EV-DO transmitter in 824.7 – 848.31 MHz band
shall be calculated at the lowest frequency (worst case) as:

824.7 / 1500 = 0.5498 mW/cm²

5. For the all frequency bands the highest level (worst case) of conducted power
and antennas gain was used for calculation. The results of calculations are
showing in Table 4.
Table 4
Power
Transmitting Ratio of the
Transmitting Antenna density at 20
Device conductive Transmitter Numeric power
frequency bands gain cm from
(transmitter) power duty cycle antenna gain density to
(MHz) (dBi) antennas
(mW) its limit
(mW/cm²)

EV-DO 824.7-848.31 959.4 100% 2.2 1.6596 0.3168 0.5762

EV-DO 1851.25-1908.8 814.7 100% 4.9 3.0903 0.5009 0.5009

802.11
2412.0-2462.0 352.0 100% 3.6 2.2909 0.1604 0.1604
b/g/n
, , , , , ,

6. Finally, the sum of ratios according (1.) and (2.) based on values in Table4.
EV-DO (800) + WiFi = 0.5762 + 0.1604 = 0.7366 < 1
C EV-DO (1900) + WiFi = 0.5009 + 0.1604 = 0.6613 < 1

Conclusion:
The Sierra Wireless EV-DO card model: MC5728 (FCC ID: N7N-MC5728), when
device transmitting antenna collocated with antennas connected to Qcom Wi-Fi card
model: Q802MKN (FCC ID: RUJ-Q802MKN) at the distance less than 20 cm and both
C C C C C C C C C C C C C

devices are integrated into the Ambient X-4000-xxx-xx smart grid node, is in compliance
C C C C C C C C C C C C

with FCC MPE limits for General Population/Uncontrolled Exposure as a mobile
device (d>20cm).

Document Created: 2010-11-09 12:45:16
Document Modified: 2010-11-09 12:45:16

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