GL-01 — Guidelines for the Measurement of Radio Frequency Fields at Frequencies from 3 KHz to 300 GHz

Appendix 2 - Measurement Procedure for Microwave Installations

1. Measurement Precautions

1.1 Field measurements should be performed only by qualified personnel, who have a good understanding of electromagnetic radiation and communication systems.

1.2 To minimize measurement errors, refer to survey meter manufacturer's guidelines regarding:

  1. environmental conditions appropriate for survey meter use (e.g. min/max limits on temperature, humidity and atmospheric pressure to maintain probe accuracy);
  2. precautions to be taken in the handling of probes to minimize lead pick-up and effects of surveyor's body (e.g. probe to be held out at arm's length facing radiator or at a right angle to the radiator, moving probe cable to see if reading is affected);
  3. symptoms of survey meter overload and precautions to be taken to avoid overload; and
  4. uncertainty of measurements taken in the presence of reflecting objects and multiple radiating sources.

1.3 The procedures that follow assume near field conditions and metering capable of indicating both E and H in units of V2/m2 and A2/m2, respectively. Conversion errors may be encountered using metering in the near field while displaying power density (which assumes far field conditions).

2. Related Documents

Reference documents are listed below:

3. Initial Preparation Before Site Visit

3.1 Establish and record the following information relating to the equipment being surveyed:

  1. equipment manufacturer, model and nomenclature;
  2. operating frequencies;
  3. transmit power;
  4. transmitting equipment LO, IF and other frequencies below 300 MHz (for H-field measurements);
  5. transmit antenna gain, beamwidth, antenna orientation (if in fixed position) or rotation angle (less than or equal to 360 degrees) and antenna dimensions;
  6. intended antenna coverage area and sector blanking (if applicable);
  7. typical duty cycle or duration of a typical (or worst-case) transmission; and
  8. applicable maximum exposure limit (MEL) from Safety Code 6.

3.2 Determine the conditions for the survey, from the list below, after discussions with technical and operations personnel:

  1. typical or worst-case equipment operating conditions;
  2. the worst-case failure mode;
  3. various frequency settings;
  4. various transmitter power levels for different modes of operation;
  5. fixed or normal antenna scan rates; and
  6. maximum transmitter power into a dummy load (if applicable).

3.3 Note any operational or technical irregularities.

3.4 Obtain a copy of previous survey results (if available) for comparison purposes.

3.5 Verify that the measurement instrumentation system will accurately measure the modulation schemes, frequency range and expected levels of interest.

4. Report Requirements

4.1 Refer to the current version of Safety Code 6 for reporting requirements.

4.2 Data may be presented as written dialogue within the main body of the survey report, in tabular form or on a site map, equipment room floor plan or equipment rack layout. The favoured method is to present survey data graphically on a top-down view of the surveyed location such as a site map or a floor plan, or on views of the transmitting equipment rack layouts.

4.3 Obtain copies of site plan and building floor plan and equipment rack layouts. Each drawing should include all prominent physical structures and/or equipment. Make multiple copies as required on which to mark the test data for the different equipment parameters and test conditions listed in paragraphs 3.1 to 3.3, applicable measurement parameter (i.e. E or H ), applicable general public or RF worker MELs and theoretical assessments of radiation exposures.

4.4 Within the report, clearly identify all over-exposure conditions and the locations where the applicable general public or RF worker MELs are reached or exceeded.

4.5 Photographs of the site, equipment room(s) and equipment rack(s) where high radiation levels are measured, would be useful for reference purposes.

4.6 Refer to paragraphs 3.1 to 3.4 for documenting equipment parameters and survey/test conditions.

5. Theoretical Assessment of Radiation Exposures

5.1 Refer to SC6 for theoretical estimation of exposure risk. Estimate the radial distance from the radiator, within the antenna coverage area, for which radiated levels will likely not exceed general public and RF worker exposure levels. The survey should begin at this distance from the radiator to reduce the risk of over-exposure to survey personnel and damaging the survey meter. Estimate whether the radiated fields to be surveyed exist under far field conditions.

6. Measurement Preliminaries On-site

6.1 Visually examine the area to be surveyed to identify:

  1. areas in which people may be physically located or pass by in transit;
  2. general public and RF worker-only areas;
  3. transmit antenna coverage area;
  4. potential re-radiators of RF energy; and
  5. metallic structures which people may grasp by hand. (Required for contact current measurements.)

6.2 Address the concerns and questions of site personnel as this may indicate the requirement for additional testing.

7. Measurement of Radiation Exposures

7.1 Consider which of the following is applicable:

If the radiator is not highly directional (i.e. beamwidth > 30 degrees), then assume far field conditions exist beyond a one metre distance for frequencies above 300 MHz. If it is estimated that far field conditions exist, then SC6 permits the measurement of either E, H or PD.

If it is estimated that near field conditions exist, then SC6 requires separate E and H measurements within the operating range of commercially available survey instrumentation. However, if it unknown whether near field or far field conditions exist, then assume near field conditions and separately measure both E and H.

7.2 The data recording procedures are as described in Section 3.

7.3 Begin the survey with the measurement of E. For ease of comparison and explanation of data to interested parties, V/m is the preferred unit of measurement. Using the manufacturers' recommended procedures, verify the operation and calibration of the survey meter with appropriate field sensor head attached.

7.4 Approach the radiator from within the antenna coverage area, starting from a distance greater than the estimated general public distance. Observe the following when taking measurements:

  1. approach the radiator by walking in a serpentine motion (i.e. left to right and then back again) across the antenna coverage area;
  2. monitor the meter instrumentation while motioning the field probe up and down, or in a circular pattern, between the knees to the top of the head;
  3. do not position your body between the radiator and the field probe. Rather, position the body so that it is to the side of the radiator-to-field-probe axis. This minimizes reflections by the body; and
  4. do not survey within 20 cm of any metallic surface or conductor.

7.5 Approach the radiator from one side of the antenna coverage area. Record the location, distance and angle from the radiator at which MELs are obtained.

7.6 Survey all areas where people may be physically located or pass by in transit and record the data.

7.7 Survey about all potential re-radiators near where people may be physically located or pass by in transit and record the data.

7.8 Refer to SC6 to determine if higher limits than the specified MELs are permissible for maximum exposure duration for time periods less than 0.1 hour.

7.9 Perform time averaging measurements should the radiated field change significantly (more than 25% per SC6) within a period of 0.1 hours, as first determined by using the maximum peak hold feature on the survey meter to record maximum change over time; otherwise a single measurement is sufficient. SC6 details the procedures to follow. Record the exposure levels incorporating time averaging. Compare these data against the applicable MEL to determine if an over-exposure condition exists.

7.10 Perform spatial averaging measurements wherever an over-exposure condition is noted. Where the field is reasonably uniform (within ± 25% per SC6), as in the far field for example, measurements in one location representative of where people may be physically located, are sufficient. SC6 details the procedures to follow. Record the exposure levels incorporating spatial averaging. Compare these data against the applicable MEL to determine if an over-exposure condition exists.

7.11 Compare measurements with previous survey results and investigate any obvious discrepancies.

7.12 Peak electric field strength measurements are only required in the vicinity of electromagnetic pulse (EMP) simulators.

7.13 Wherever MELs are reached or exceeded, repeat paragraphs 7.3 to 7.10, using instrumentation to measure H, in units of A2/m2.

7.14 Repeat the steps for all conditions of interest as determined by paragraphs 3.1 to 3.3.

8. Induced Current Measurements

8.1 Determine the minimal set of survey locations applicable to Induced Current measurement program by the following:

Identify those locations and equipment operating conditions for which the above radiative measurement program produced over-exposure conditions before spatial and time averaging were applied;

From this set, identify those locations for which the equipment being surveyed was operating within the frequency range for which induced current measurements are applicable. (Refer to SC6); and

Identify those locations, if any, where there are long vertical metallic lengths. Examples include metallic poles, stands, stanchions, fence posts, hoists and cables. Add these locations to above set of minimal survey locations for induced current measurements.

8.2 Position the human model complete with tripod assembly at the first measurement location.

8.3 Calibrate/Zero the survey instrumentation.

8.4 Power ON the equipment at an appropriate equipment operating condition. Record the induced current produced by the test instrumentation. Do not apply time or spatial averaging to the measured results.

8.5 Repeat for all radiation over-exposure conditions and for all applicable equipment operating conditions.

8.6 Most induced current meters develop measurement data valid for both feet. For data comparison against the single foot MEL condition, as required by SC6, it is valid to measure the current through both feet and then divide by two if using this type of instrument.

8.7 Refer to SC6 to determine if higher limits than the specified MELs are permissible for maximum exposure duration for time periods less than 0.1 hour.

8.8 Perform time averaging measurements or investigations should the radiated field change significantly (more than 25% per SC6) within a period of 0.1 hours. Otherwise a single measurement is sufficient. SC6 details the procedures to follow. Record the exposure levels incorporating time averaging. Compare this data against the applicable MEL to determine if an over-exposure condition does indeed exist.

8.9 Perform spatial averaging measurements wherever an over-exposure condition is noted. (Where the field is reasonably uniform (within ± 25% per SC6), as in the far field for example, a single measurements is sufficient). SC6 details the procedures to follow. Record the exposure levels incorporating spatial averaging. Compare this data against the applicable MEL to determine if an over-exposure condition does indeed exist.

9. Contact Current Measurements

9.1 Determine the minimal set of survey locations applicable to contact current measurement program by the following:

  1. identify those locations were the radiation measurements produced over-exposure results before spatial and time averaging were applied;
  2. from this set, identify those locations for which the equipment being surveyed was operating within the frequency range for which contact current measurements are applicable. (Refer to SC6);
  3. from this set, identify those locations for which a person may come into contact with a metallic object by hand-grip. Select these the locations as where contact current measurements are required as a minimum; and
  4. identify those locations, if any, where there are long, vertical metallic lengths or sharp metallic edges. (Examples include metallic poles, stands, stanchions, fence posts, hoists and cables). Add these locations to the above set of minimal survey locations for contact current measurements.

9.2 Position the test instrumentation ground plate and meter on ground or floor level, at the first measurement location.

9.3 Fully extend the test instrumentation cabling connecting the ground plate to the meter probe tip assembly in a vertical plane. Ensure the cable pair between the ground plate and meter probe tip assembly are not twisted. Ensure the cable pair maintains a fixed separation distance between each other. Touch the meter probe tip assembly at the metallic location where a person may hand grip metal.

9.4 Calibrate/Zero the survey instrumentation.

9.5 Power ON the equipment at an appropriate equipment operating condition. Record the contact current produced by the test instrumentation. Do not apply time or spatial averaging to the measured results.

9.6 Repeat for all radiative over-exposure conditions and for all applicable equipment operating conditions.

9.7 Most contact current meters develop measurement data valid for both feet. For data comparison against the single foot MEL condition, as required by SC6, it is valid to measure the current through both feet and then divide by two if using this type of instrument.

9.8 Refer to SC6 to determine if higher limits than the specified MELs are permissible for maximum exposure duration for time periods less than 0.1 hour.

9.9 Perform time averaging measurements or investigations should the radiated field change significantly (more than 25% per SC6) within a period of 0.1 hours. Otherwise a single measurement is sufficient. SC6 details the procedures to follow. Record the exposure levels incorporating and time averaging. Compare this data against the applicable MEL to determine if an over-exposure condition does indeed exist.

9.10 Perform spatial averaging measurements wherever an over-exposure condition is noted. (Where the field is reasonably uniform (within ± 25% per SC6), as in the far field for example, a single measurements is sufficient). SC6 details the procedures to follow. Record the exposure levels incorporating spatial averaging. Compare this data against the applicable MEL to determine if an over-exposure condition does indeed exist.

10. Radiation Measurements about Transmitting Equipment

10.1 The procedures that follow are applicable to radiation measurements on in-service transmitting equipment in equipment rooms and equipment bays, about equipment maintenance/workshop areas and calibration centres.

10.2 Inspect cabinet interlocks to ensure they are operating satisfactorily. Discuss maintenance and operational procedures about the transmitting cabinets performed by maintenance and operational support staff. For example, determine if cabinet door interlocks are defeated for repair or calibration procedures. Test equipment operating under these non-standard interlock configurations.

10.3 The data recording procedures are as described in Section 4 of GL-001.

10.4 Using a calibrated meter with E field probe, survey all personnel workstation areas. Survey those areas where personnel may position themselves or position their body extremities such as arms and hands.

10.5 Visually examine all waveguide joints for indications of high-voltage arcing, in areas where personnel may position themselves or position their body extremities. If waveguide arcing is noted, immediately report it to the equipment maintainers. Cease operation of the transmitting system until the source of the problem has been identified and corrected.

10.6 Survey along RF output power cables, operating dummy loads, exterior waveguides, spaces between rack panels, etc. Note locations of standing waves. Ignore all measurements made within 20 cm of a metallic surface, cable or RF device.

10.7 For each over-exposure condition, and for all equipment racks generating RF energy at frequencies below 300 MHz, repeat the measurements with a magnetic (H field) probe and record the levels found.

10.8 Refer to SC6 to determine if higher limits than the specified MELs are permissible for maximum exposure duration for time periods less than 0.1 hour.

10.9 Perform time averaging measurements should the radiated field change significantly (more than 25% per SC6) within a period of 0.1 hours, as first determined by using the maximum peak hold feature on the survey meter to record maximum change over time; otherwise a single measurement is sufficient. SC6 details the procedures to follow. Record the exposure levels incorporating time averaging. Compare these data against the applicable MEL to determine if an over-exposure condition exists.

10.10 Perform spatial averaging measurements wherever an over-exposure condition is noted. Where the field is reasonably uniform (within ± 25% per SC6), as in the far field for example, measurements in one location representative of where people may be physically located, are sufficient. SC6 details the procedures to follow. Record the exposure levels incorporating spatial averaging. Compare these data against the applicable MEL to determine if an over-exposure condition exists.

10.11 Compare measurements with previous survey results and investigate any obvious discrepancies.

10.12 Peak electric field strength measurements are only required in the vicinity of EMP simulators.

11. Abbreviations and Acronyms

H
Magnetic Field
E
Electric Field
PD
Power Density
MEL
Maximum Exposure Level (from SC6)
SC6
Health Canada's Safety Code 6
RF
Radiofrequency