RF Exposure Evaluation for Amateur Radio Operators

1
RF Exposure Evaluation for Amateur Radio Operators

• Marc C. Tarplee, Ph.D.
• Technical Coordinator, SC Section

2
Overview

• This presentation is meant to be a brief
  introduction to RF exposure (RFE) rules
  promulgated by the FCC in1998 and RFE evaluation
  as it applies to amateur stations.
• For a comprehensive treatment of the FCC rules
  and evaluation techniques, see RF Exposure and
  You, by Ed Hare, W1RFI. The book is available
  from ARRL for 15.

3
A Brief Review of the FCC RF Exposure Rules
4
The FCCs RF Exposure Rules

• On 1 January 1998, new FCC rules regarding RF
  Exposure (RFE) went into effect.
• RFE rules were not new the first FCC rules for
  RFE date back to 1985.
• The new rules no longer exempted amateurs from
  MPE limits.
• The rules set new limits on the maximum
  permissible exposure (MPE) allowed from radio
  transmitters.

5
Major Points of the New Rules

• Set RF exposure limits that are consistent with
  the manner in which the human body absorbs RF.
• Require stations regulated by the FCC to meet the
  guidelines or file an environmental assessment.
• Permit amateurs to perform their own evaluation
  of their station.
• Provide categorical exemptions from RFE
  evaluation for stations whose power, frequency,
  duty cycle, etc. are such that compliance may be
  assumed.

6
RF Environments

• The FCC rules define two classes of RF
  environments
• Controlled an environment in which people are
  aware of their RF exposure and are able to take
  action to reduce their exposure if necessary.
  Exposure in this environment is averaged over a 6
  minute period.
• Uncontrolled an environment accessible by the
  general public, who may not be aware of their RF
  exposure. Exposure in this environment is
  averaged over a 30 minute period.

7
RF Environments

• Typically, the controlled environment is an
  amateurs residence and yard.
• The uncontrolled environment is everything else

8
RF Exposure Limits
Freq Range (MHz) Controlled Environment (6 minute average) Controlled Environment (6 minute average) Controlled Environment (6 minute average) Uncontrolled Environment (30 minute average) Uncontrolled Environment (30 minute average) Uncontrolled Environment (30 minute average)
Freq Range (MHz) E Field strength (V/m) H Field strength (A/m) Power Density (mW/cm2) E Field strength (V/m) H Field strength (A/m) Power Density (mW/cm2)
0.3- 3 614 1.63 100 ------ ------ ------
3 - 30 1842/f 4.89/f 900/f 2 ------ ------ ------
0.3-1.34 ------ ------ ------ 614 1.63 100
1.34-30 ------ ------ ------ 824/f 2.19/f 180/f 2
30-300 61.4 0.163 1.0 27.5 0.073 0.2
300-1500 ------ ------ f/300 ------ ------ f/1500
gt1500 ------ ------ 5 ------ ------ 1.0

• Note that the limits are field strength limits,
  not power limits!!

9
MPE Chart
10
Field Strength vs. Power

• Although the limits are given in terms of field
  strength, it is possible to relate them to
  transmitted power and the distance from the
  measurement point to the antenna, quantities
  which most amateurs are able to measure.
• The FCCs OET Bulletin 65 contains numerous
  tables for this purpose, so it is not necessary
  to directly measure the field strength.

11
Time-Weighted Averages

• The limits are time-weighted averages.
• The exposure is averaged over the specified time
  period to get the average value.
• Here is an example
• A person is exposed for 4 minutes to an electric
  field of 700 V/m. What is the time-weighted
  exposure in a controlled environment?
• Solution
• Avg RFE (Field strengthtime)/weighting period
• (7004)/6 2800/6 467 V/m

12
Time-Weighted Averages

• The example can be reworked for the uncontrolled
  environment, for which the weighting period is 30
  minutes
• Solution
• Avg RFE (Field strengthtime)/weighting period
• (7004)/30 2800/30 93 V/m

13
Exemptions from Evaluation

• There are 4 categorical exemptions for amateur
  stations
• Amateur stations whose PEP antenna input power is
  less than that shown in the table on the next
  page.
• Amateur repeaters whose ERP is 500 W or less.
• Amateur repeaters with antennas not mounted on
  buildings, if the antenna is located more than 10
  m (32 ft 9 5/8 in) above ground.
• Amateur mobile and portable hand-held stations
  using push-to-talk of equivalent operation.

14
Power Limits for Amateur RFE Evaluation Exemption
Bands Upper Power Limit (PEP)
160m 40m 500 W
30m 425 W
20m 225 W
17m 125 W
15m 100 W
12m 75 W
10m 1.25 m 50 W
70cm 70 W
33cm 150 W
23 cm 200 W
13 cm and above 250 W

• Input power to the antenna

15
Amateur Station RFE Evaluation
16
The Evaluation Process

• Determine whether the station meets the standard
  for a categorical exemption on any of the bands
  of operation, and exclude these bands.
• Determine which evaluation technique will be
  used
• Tables developed from far-field power density
  formulas
• Tables developed from antenna modeling
• Modeling of the actual antenna farm
• Graphs made from power-density formulas
• Field strength software
• Calibrated field strength methods
• Select a method for determining RF power
• PEP
• Time weighted average

17
RFE Evaluation Example

• We will make an evaluation of station N4UFP using
  tables developed from the far-field power density
  formulas.
• Evaluation will be done using PEP power and
  average power.
• The PEP power/far-field table approach is very
  conservative and is the easiest to do, thus it
  should be done first.

18
Station N4UFP

• 160m/80m/75m/40m
• vertical loops 40 feet from shack, 40 feet from
  property line
• Max power 1000 W SSB/500 CW
• 20,15,10m
• tribander at 50 ft, located 45 feet from the
  shack, 55 feet from property line
• Max power 1000 W SSB/500 CW
• 6m
• 5 element yagi up 54 feet, located 45 feet from
  shack , 55 feet from property line
• Max power 300 W
• 2m
• 13 element yagi up 57 feet, located 45 feet from
  shack , 55 feet from property line
• Max power 100 W
• 70cm
• 25 element yagi up 60 feet, located 45 feet from
  shack , 55 feet from property line
• Max power 55 W

19
Step 1 Check for Exemptions

• Referring to the table on slide 14 of this
  presentation, we see that only N4UFPs 70cm
  operation is exempt from evaluation.

20
PEP/Far Field Evaluation Method

• The Far-field tables (Table 4a ,Table 4b-VHF, and
  Table 4b-UHF of supplement B to OET Bulletin 65)
  show the minimum compliance distance as a
  function of antenna gain, frequency and antenna
  input power and the type of environment.
• The minimum compliance distance is the minimum
  distance at which the E and H fields fall below
  the RFE limits shown in slide 7.

21
Measuring Distances
Minimum distance from house to antenna

• The diagram to the right shows a typical wire
  antenna installation
• For RFE compliance purposes, the distance to the
  antenna is the shortest distance from the point
  of exposure to the any part of the antenna.

22
Measuring Distances

• The diagram to the right shows a typical tower
  mounted antenna
• For RFE compliance purposes, the distance to the
  antenna is the shortest distance from the point
  of exposure to the any part of the antenna.
• The Pythagorean theorem can be used to compute
  the distance D

23
160m Evaluation

• Antenna Gain 3 dBi (single quad loop)
• Max input power 1000 W PEP.
• Operating frequency 2 MHz
• From Table 4a , the compliance distances are
• Controlled environment 0.6m 2.0 feet
• Uncontrolled environment 1.06m 3.5 feet
• Since this antenna is 40 feet from the shack and
  40 feet from the property line, N4UFPs 160m
  operation is in compliance

24
80/75m Evaluation

• Antenna Gain 3 dBi (single quad loop)
• Max input power 1000 W PEP.
• Operating frequency 4 MHz
• From Table 4a , the compliance distances are
• Controlled environment 0.9m 3.0 feet
• Uncontrolled environment 1.9m 6.2 feet
• Since this antenna is 40 feet from the shack and
  40 feet from the property line, N4UFPs 80/75m
  operation is in compliance

25
40m Evaluation

• Antenna Gain 3 dBi (single quad loop)
• Max input power 1000 W PEP.
• Operating frequency 7.3 MHz
• From Table 4a , the compliance distances are
• Controlled environment 1.6m 5.2 feet
• Uncontrolled environment 3.5m 11.5 feet
• Since this antenna is 40 feet from the shack and
  40 feet from the property line, N4UFPs 40m
  operation is in compliance

26
20m Evaluation

• Antenna Gain 9 dBi (3-el Yagi)
• Max input power 1000 W PEP.
• Operating frequency 14.35 MHz
• From Table 4a , the compliance distances are
• Controlled environment 6.1m 20 feet
• Uncontrolled environment 13.6m 44.6 feet
• This antenna is 50 ft above ground and the tower
  is 45 ft from the shack, so the distance to the
  shack is sqrt(502452) sqrt(25002025)
  sqrt(4525) 67 ft.
• By similar reasoning, the distance to the
  property line is 74 ft
• N4UFPs 20 m operation is in compliance.

27
15m Evaluation

• Antenna Gain 9 dBi (3-el Yagi)
• Max input power 1000 W PEP.
• Operating frequency 21.45 MHz
• From Table 4a , the compliance distances are
• Controlled environment 9.1m 29.8 feet
• Uncontrolled environment 20.3m 66.6 feet
• This antenna is 67 ft from the shack and 74 ft
  from the property line
• N4UFPs 15 m operation is in compliance.

28
10m Evaluation

• Antenna Gain 9 dBi (3-el Yagi)
• Max input power 1000 W PEP.
• Operating frequency 29.7 MHz
• From Table 4a , the compliance distances are
• Controlled environment 12.6m 41.3 feet
• Uncontrolled environment 28.2m 92.5 feet
• This antenna is 67 ft from the shack and 74 ft
  from the property line.
• N4UFPs 10 m operation may not be in compliance.

29
6m Evaluation

• Antenna Gain 12 dBi (5-el Yagi)
• Max input power 300 W PEP (use 500W entries).
• Operating frequency 50 MHz
• From Table 4b , the compliance distances are
• Controlled environment 12.7m 41.7 feet
• Uncontrolled environment 28.4m 93.2 feet
• This antenna is 70 ft from the shack and 77 ft
  from the property line.
• N4UFPs 10 m operation may not be in compliance.

30
2m Evaluation

• Antenna Gain 15 dBi (13-el Yagi)
• Max input power 100 W PEP.
• Operating frequency 144 MHz
• From Table 4b , the compliance distances are
• Controlled environment 8m 26.2 feet
• Uncontrolled environment 18m 59.0 feet
• This antenna is 73 ft from the shack and 79 ft
  from the property line.
• N4UFPs 2 m operation is in compliance.

31
Average Power/Far Field Evaluation Method

• N4UFP may not be compliant on the following
  bands 10m and 6m.
• The FCC rules are based on time weighted
  averages, rather than PEP, so a more detailed
  analysis using average power will be made for
  these bands.
• Note that the simple evaluation using PEP is very
  conservative a station compliant using PEP will
  always be compliant using the average power.

32
Determining Average Power

• Average power is given by
• Pavg (PEP)(Duty Factor)(time)/(weighting
  period)
• To be conservative, we will assume
• That CW is the dominant mode of operation. Then
  the duty cycle 0.4
• That transmissions are approximately 3 minutes in
  length with 3 minute listening periods in
  between.

33
10 m Avg. Power Evaluation

• The maximum PEP on 10m 1000 W with gain 9 dbi
• The average power for controlled environments is
• Pavg,c (1000)(0.4)(3)/6 200 W
• The average power for uncontrolled environments
  is
• Pavg,uc (1000)(0.4)(15)/30 200 W
• There is no 200 W column on Table 4a , so we must
  interpolate between the 100 and 500W columns. The
  compliance distances are
• Controlled environment 5.7m 18.6 feet
• Uncontrolled environment 12.6m 41.3 feet
• This antenna is 67 ft from the shack and 74 ft
  from the property line, so N4UFPs 10 m operation
  is in compliance.

34
6 m Avg. Power Evaluation

• The maximum PEP on 6m 300 W with gain 12 dBi
• The average power for controlled environments is
• Pavg,c (300)(0.4)(3)/6 60 W
• The average power for uncontrolled environments
  is
• Pavg,uc (1000)(0.4)(15)/30 60 W
• There is no 60 W column on Table 4b , so we must
  interpolate between the 50 and 100W columns. The
  compliance distances are
• Controlled environment 4.4m 14.4 feet
• Uncontrolled environment 9.9m 32.3 feet
• This antenna is 67 ft from the shack and 74 ft
  from the property line, so N4UFPs 6 m operation
  is in compliance.

35
What if I am not compliant?

• If an amateur station is not compliant on a
  particular band/mode combination, the following
  actions can be taken
• Reduce transmitter power.
• Relocate the antenna to place inhabited areas
  beyond the minimum compliance distance.
• Cease operation on that band/mode

36
Recordkeeping

• The FCC does not require amateurs to keep a
  written record of their RFE evaluation
• However, an amateur must be able to demonstrate
  that his/her station is compliant with RFE rules,
  should the FCC request it.

37
Summary

• You should now be able to make a simple
  evaluation of your amateur station for RFE using
  either PEP or average power techniques.
• More detailed information can be obtained from
  FCC OET Bulletin 65, or RF Exposure and You
  available from ARRL.
• I will be happy to assist in your RFE evaluation.

38
RFE Tables from OET Bulletin 65
39
TABLE 4a. (MF/HF Bands)

• (Developed by Fred Maia, W5YI Group, working in
  cooperation with the ARRL.)
• Estimated distances in meters from transmitting
  antennas necessary to meet FCC power density
  limits for
• Maximum Permissible Exposure (MPE) for either
  occupational/ controlled exposures (Con) or
  general
• population/uncontrolled exposures (Unc) using
  typical antenna gains for the amateur service and
• assuming 100 duty cycle and maximum surface
  reflection. Chart represents worst case scenario.
• Freq. Antenna
• (MF/HF) Gain Peak Envelope Power (watts)
• (MHz/Band) (dBi) 100 watts 500 watts 1000
  watts 1500 watts
• Con. Unc. Con. Unc Con. Unc. Con. Unc.
• 2.0 (160m) 0 0.1 0.2 0.3 0.5 0.5 0.7
  0.6 0.8
• 2.0 (160m) 3 0.2 0.3 0.5 0.7 0.6
  1.06 0.8 1.2
• 4.0 (75/80m) 0 0.2 0.4 0.4 1.0 0.6
  1.3 0.7 1.6
• 4.0 (75/80m) 3 0.3 0.6 0.6 1.3 0.9
  1.9 1.0 2.3
• 7.3 (40m) 0 0.3 0.8 0.8 1.7 1.1
  2.5 1.3 3.0
• 7.3 (40m) 3 0.5 1.1 1.1 2.5 1.6
  3.5 1.9 4.2
• 7.3 (40m) 6 0.7 1.5 1.5 3.5 2.2
  4.9 2.7 6.0
• 10.15 (30m) 0 0.5 1.1 1.1 2.4 1.5
  3.4 1.9 4.2
• 10.15 (30m) 3 0.7 1.5 1.5 3.4 2.2
  4.8 2.6 5.9
• 10.15 (30m) 6 1.0 2.2 2.2 4.8 3.0
  6.8 3.7 8.3

40
Table 4b. (VHF Bands)

• (Developed by Fred Maia, W5YI Group, working in
  cooperation with the ARRL.)
• Estimated distances in meters from transmitting
  antennas necessary to meet FCC power density
  limits for
• Maximum Permissible Exposure (MPE) for either
  occupational/ controlled exposures (Con) or
  general
• population/uncontrolled exposures (Unc) using
  typical antenna gains for the amateur service and
• assuming 100 duty cycle and maximum surface
  reflection. Chart represents worst case scenario.
• Freq Antenna
• (VHF/UHF) Gain Peak Envelope Power (watts)
• (MHz/Band) (dBi) 50 watts 100 watts 500 watts
  1000 watts
• Con. Unc. Con. Unc Con. Unc. Con. Unc.
• 50 (6m) 0 1.0 2.3 1.4 3.2 3.2
  7.1 4.5 10.1
• 50 (6m) 3 1.4 3.2 2.0 4.5 4.5
  10.1 6.4 14.3
• 50 (6m) 6 2.0 4.5 2.8 6.4 6.4
  14.2 9.0 20.1
• 50 (6m) 9 2.8 6.4 4.0 9.0 9.0
  20.1 12.7 28.4
• 50 (6m) 12 4.0 9.0 5.7 12.7 12.7
  28.4 18.0 40.2
• 50 (6m) 15 5.7 12.7 8.0 18.0 18.0 40.2
  25.4 56.8
• 144 (2m) 0 1.0 2.3 1.4 3.2 3.2
  7.1 4.5 10.1
• 144 (2m) 3 1.4 3.2 2.0 4.5 4.5
  10.1 6.4 14.3
• 144 (2m) 6 2.0 4.5 2.8 6.4 6.4
  14.2 9.0 20.1
• 144 (2m) 9 2.8 6.4 4.0 9.0 9.0
  20.1 12.7 28.4

41
Table 4b. (UHF Bands)

• (Developed by Fred Maia, W5YI Group, working in
  cooperation with the ARRL.)
• Estimated distances in meters from transmitting
  antennas necessary to meet FCC power density
  limits for
• Maximum Permissible Exposure (MPE) for either
  occupational/ controlled exposures (Con) or
  general
• population/uncontrolled exposures (Unc) using
  typical antenna gains for the amateur service and
• assuming 100 duty cycle and maximum surface
  reflection. Chart represents worst case scenario.
• Freq Antenna
• (VHF/UHF) Gain Peak Envelope Power (watts)
• (MHz/Band) (dBi) 50 watts 100 watts 500 watts
  1000 watts
• Con. Unc. Con. Unc Con. Unc. Con. Unc.
• 450 (70cm) 3 1.2 2.6 1.6 3.7 3.7
  8.2 5.2 11.6
• 450 (70cm) 6 1.6 3.7 2.3 5.2 5.2 11.6
  7.4 16.4
• 450 (70cm) 9 2.3 5.2 3.3 7.3 7.3 16.4
  10.4 23.2
• 450 (70cm) 12 3.3 7.3 4.6 10.4 10.4 23.2
  14.7 32.8
• 902 (33cm) 0 0.6 1.3 0.8 1.8 1.8
  4.1 2.6 5.8
• 902 (33cm) 3 0.8 1.8 1.2 2.6 2.6
  5.8 3.7 8.2
• 902 (33cm) 6 1.2 2.6 1.6 3.7 3.7
  8.2 5.2 11.6
• 902 (33cm) 9 1.6 3.7 2.3 5.2 5.2
  11.6 7.3 16.4
• 902 (33cm) 12 2.3 5.2 3.3 7.3 7.3
  16.4 10.4 23.2
• 1240 (23cm) 0 0.5 1.1 0.7 1.6 1.6
  3.5 2.2 5.0

42
TABLE 4a.

• (Developed by Fred Maia, W5YI Group, working in
  cooperation with the ARRL.)
• Estimated distances in meters from transmitting
  antennas necessary to meet FCC power density
  limits for
• Maximum Permissible Exposure (MPE) for either
  occupational/ controlled exposures (Con) or
  general
• population/uncontrolled exposures (Unc) using
  typical antenna gains for the amateur service and
• assuming 100 duty cycle and maximum surface
  reflection. Chart represents worst case scenario.
• Freq. Antenna
• (MF/HF) Gain Peak Envelope Power (watts)
• (MHz/Band) (dBi) 100 watts 500 watts 1000
  watts 1500 watts
• Con. Unc. Con. Unc Con. Unc. Con. Unc.
• 2.0 (160m) 0 0.1 0.2 0.3 0.5 0.5 0.7
  0.6 0.8
• 2.0 (160m) 3 0.2 0.3 0.5 0.7 0.6
  1.06 0.8 1.2
• 4.0 (75/80m) 0 0.2 0.4 0.4 1.0 0.6
  1.3 0.7 1.6
• 4.0 (75/80m) 3 0.3 0.6 0.6 1.3 0.9
  1.9 1.0 2.3
• 7.3 (40m) 0 0.3 0.8 0.8 1.7 1.1
  2.5 1.3 3.0
• 7.3 (40m) 3 0.5 1.1 1.1 2.5 1.6 3.5
  1.9 4.2
• 7.3 (40m) 6 0.7 1.5 1.5 3.5 2.2
  4.9 2.7 6.0
• 10.15 (30m) 0 0.5 1.1 1.1 2.4 1.5
  3.4 1.9 4.2
• 10.15 (30m) 3 0.7 1.5 1.5 3.4 2.2
  4.8 2.6 5.9
• 10.15 (30m) 6 1.0 2.2 2.2 4.8 3.0
  6.8 3.7 8.3

43
Table 4b. (VHF Bands)

• (Developed by Fred Maia, W5YI Group, working in
  cooperation with the ARRL.)
• Estimated distances in meters from transmitting
  antennas necessary to meet FCC power density
  limits for
• Maximum Permissible Exposure (MPE) for either
  occupational/ controlled exposures (Con) or
  general
• population/uncontrolled exposures (Unc) using
  typical antenna gains for the amateur service and
• assuming 100 duty cycle and maximum surface
  reflection. Chart represents worst case scenario.
• Freq Antenna
• (VHF/UHF) Gain Peak Envelope Power (watts)
• (MHz/Band) (dBi) 50 watts 100 watts 500 watts
  1000 watts
• Con. Unc. Con. Unc Con. Unc. Con. Unc.
• 50 (6m) 0 1.0 2.3 1.4 3.2 3.2
  7.1 4.5 10.1
• 50 (6m) 3 1.4 3.2 2.0 4.5 4.5
  10.1 6.4 14.3
• 50 (6m) 6 2.0 4.5 2.8 6.4 6.4
  14.2 9.0 20.1
• 50 (6m) 9 2.8 6.4 4.0 9.0 9.0
  20.1 12.7 28.4
• 50 (6m) 12 4.0 9.0 5.7 12.7 12.7
  28.4 18.0 40.2
• 50 (6m) 15 5.7 12.7 8.0 18.0 18.0 40.2
  25.4 56.8
• 144 (2m) 0 1.0 2.3 1.4 3.2 3.2
  7.1 4.5 10.1
• 144 (2m) 3 1.4 3.2 2.0 4.5 4.5
  10.1 6.4 14.3
• 144 (2m) 6 2.0 4.5 2.8 6.4 6.4
  14.2 9.0 20.1
• 144 (2m) 9 2.8 6.4 4.0 9.0 9.0
  20.1 12.7 28.4