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RF Exposure Analysis

John MacDuff KA7TTY

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RF Environmental Evaluation

  • Renew ham license
  • Change ham license
  • By May 3, 2023

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*whichever comes first.

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Evaluations can be made in Tiers.

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Four Tiers

Tier 1 – Need Antenna location and transmitter ERP.

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Tier 2 – Calculate the Maximum Permissible Exposure (MPE) in terms

        • E field
        • H field
        • Power Density.

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Tier 3 and 4

Tier 3 - Account for

        • Antenna type
        • Signal direction
        • Length and type of feed line
        • Duty cycle of your operating mode

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Tier 4 - Model your antenna installation

determine the antenna pattern of your antennas

see what the energy is at the locations in question.

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Incidental and Occupational Exposure

Incidental Exposure

you do not know you are being exposed.

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Occupational Exposure

yourself and members of your household.

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*In Near Field of your antenna.

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So where to start?

List of your antennas

Map of your lot.

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Antenna

1

80m ½ wave dipole

2

220 MHz dipole

3

440 MHz yagi

4

2.4 G Mesh

5

2m dipole

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Add your antennas

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Estimate distances

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Antenna

Distance Measured

1

80m ½ wave dipole

A = 6.22m, E = 10.99m

2

220 MHz dipole

B = 21.30m

3

440 MHz yagi

B = 21.30m

4

2.4 G Mesh

C = 19.93m

5

2m dipole

D = 22.23m

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Add distances to the map

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ERP Limits for Tier 1

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Calculate Safe ERP Limits�Incidental Exposure

Antenna

Band

Height (h)

6-foot person

Distance (d)

h2

d2

Sum

Feet

R Meters

Factor

f(MHz)

ERP Limit (W)

My ERP

1-A

20m

10

4

20

16

400

416

20.39608

6.216725

3450

14.35

647.4981753

100

2

220

29

23

66

529

4356

4885

69.89278

21.30332

3.83

220

1738.174072

25

3

440

29

23

66

529

4356

4885

69.89278

21.30332

0.0128

440

2555.978165

5

4

2.4G

29

23

60

529

3600

4129

64.2573

19.58562

19.2

2400

7365.055721

0.1

5

2m

37

31

66

961

4356

5317

72.91776

22.22533

3450

148

77.8022667

25

1-E

20m

26

20

30

400

900

1300

36.05551

10.98972

3450

14.35

2023.431798

100

1-A

80m

26

4

20

16

400

416

20.39608

6.216725

3450

4

8333.402688

100

1-A

40m

26

4

20

16

400

416

20.39608

6.216725

3450

14.35

647.4981753

100

1-E

80m

26

20

30

400

900

1300

36.05551

10.98972

3450

4

26041.8834

100

Limit

Mine

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Check for Near Field

Antenna

Band

λ

feet

λ/2π

My R (ft)

1-A

20m

20m

65.61

10.3 ft

20.39

2

220

1.36m

4.46

7.8 in

69.89

3

440

0.68m

2.23

4.3 in

69.89

4

2.4G

0.125m

0.41

~0

64.26

5

2m

2m

6.56

1 ft

72.92

1-E

20m

20m

65.61

10.3 ft

36.06

1-A

80m

80m

262.47

41.3 ft

20.39

1-A

40m

40m

131.23

20.7 ft

20.29

1-E

80m

80m

262.47

41.3 ft

36.06

λ/2π

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Tier 2 Calculations�Near Field and Occupational Exposure

 

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Near Field Calculations

S

E

H

Antenna

P

G

R cm

S (mW/cm2)

limit

E (V/m)

limit

H (A/m)

limit

1-A

100000

2.2

621.6725

0.04529913

4.38 @ 14.35MHz

13.06819512

128.4

0.034664

0.341

1-A

100000

2.2

621.6725

0.04529913

4.38 @ 14.35MHz

13.06819512

128.4

0.034664

0.341

1-E

100000

2.2

1098.972

0.01449572

4.38 @ 14.35MHz

7.392488191

128.4

0.019609

0.341

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Occupational Exposure Map

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Tier 2 Calculations

* On this band, the limit is specified only by Power Density (S).

S

E

H

Antenna

Band

Height (h)

6-foot person

d

h2

d2

Sum

Feet

R Meters

P

G

R

S (mW/cm2)

limit

E (V/m)

limit

H (A/m)

limit

1a

HF

10

4

0

​

​

​

4

1.2192

100000

2.2

121.92

1.17777756

4.38 @ 14.35MHz

66.63499

128.4

0.176751

0.341

1b

HF

26

20

0

​

​

​

20

6.096

100000

2.2

609.6

0.047111102

4.38 @ 14.35MHz

13.327

128.4

0.03535

0.341

1c

HF

12

​

0

​

​

​

12

3.6576

100000

2.2

365.76

0.130864173

4.38 @ 14.35MHz

22.21166

128.4

0.058917

0.341

1d

HF

16

​

4

256

16

272

16.49242

5.02689

100000

2.2

502.689

0.069281033

4.38 @ 14.35MHz

16.16136

128.4

0.042868

0.341

1e

HF

5

​

0

​

​

​

5

1.524

100000

2.2

152.4

0.753777639

4.38 @ 14.35MHz

53.30799

128.4

0.141401

0.341

1f

HF

6

​

0

​

​

​

6

1.8288

100000

2.2

182.88

0.523456693

4.38 @ 14.35MHz

44.42332

128.4

0.117834

0.341

2a

220

8

​

0

​

​

​

8

2.4384

25000

2.2

243.84

0.073611098

1.0

16.65875

61.4

0.044188

0.163

3

440

8

​

0

​

​

​

8

2.4384

5000

2.2

243.84

0.01472222

1.4

-

*

-

*

4

2.4G

21

​

0

​

​

​

21

6.4008

100

2.2

640.08

4.27312E-05

5.0

-

*

-

*

5

2m

21

​

0

​

​

​

21

6.4008

25000

2.2

640.08

0.01068279

1.0

6.346189

61.4

0.016833

0.163

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Conclusion

  • We are now done

and do not need to progress to Tier 3.

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  • If you need to progress to Tier 3

Calculator like the Lake Washington Ham Club has on their WEB site.

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References

  1. RF Exposure and You, by Ed Hare, W1RFI, ARRL
  2. Changes to FCC RF Exposure Rules 2021, Gregory Lapin, PhD, PE, N9GL, ARRL
  3. Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields, OTC Bulletin 65, and Supplement B
  4. RF Exposure Calculator, Lake Washington Ham Club, http://www.lakewashingtonhamclub.org/resources/rf-exposure-calculator/

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