GL-01 — Guidelines for the Measurement of Radio Frequency Fields at Frequencies from 3 KHz to 300 GHz
Section A - Procedures for Measuring the Levels of RF Energy Associated With Land Mobile, Cellular and PCS Services
This appendix covers transmitting facilities involving land mobile, paging, two-way, trunking, cellular and PCS services, operating in the frequency range of 30 MHz to 2 GHz. Field measurements should be performed by qualified personnel who have a good understanding of wireless operations and facilities. All channels should be turned on at the same time and operating at full power to achieve worst-case situations.
2. Related Documents
Pertinent documents on the subject of non-ionizing radiation (NIR) are listed below:
- Health Canada, Limits of Human Exposure to Radiofrequency Electromagnetic Fields in the Frequency Range from 3 kHz to 300 GHz, Safety Code 6, 1999.
- CRC Predict Program - Propagation Prediction Program developed by Communications Research Centre for the VHF/ UHF Radio Frequency Bands.
- Radio Frequency Power Density calculation Tool (RaPD Tool). Members can obtain a copy from the CWTA. Otherwise, copies are available from Previse Inc.
3. Initial Preparation
3.1 Station and Site Information
3.1.1 One should obtain the pertinent station and site parameters prior to conducting the survey, but if the information is not complete, collect the necessary data at the site.
Station and site parameters include:
- ground elevation - above mean sea level (AMSL)
- height - above ground level (AGL)
- the number of antennas located at the site
- height (with respect to the floor or ground)
- antenna patterns
- operating frequency range
- mechanical dimensions
- number of transmitters - transmit power
- operating frequency
3.1.2 Nearby transmitting stations may affect the field readings, therefore they should be taken into account in the prediction of the flux density at each test point. In general, databases and maps should be searched for any transmitting station within a radius of 200 m of the survey site and any high-power transmissions (e.g. AM broadcasting or radar) within 2 km.
Note: When dealing with an antenna farm, a copy of the site drawing indicating the antenna layout, relative position and site characteristics should be obtained. Photos would also be helpful.
3.2 Theoretical Estimate
3.2.1 Establishing grids for measurements around survey station
220.127.116.11 If multiple transmitting antennas are present at various locations at the site, designate a single reference point for estimation purposes.
18.104.22.168 Calculate the distance from the reference point to where the far field begins, using the appropriate equation.
For large antennas:
For small antennas:
Where "Rf" is the distance from the reference point that marks the beginning of the far fields (m)
"D" is the largest dimension of the antenna (m)
"λ" is the wavelength (m)
22.214.171.124 Find the minimum distance from the reference point where the following conditions hold.
R ≥ Rf
Where, "R" is the distance from the reference point, refer to as "maximum grid distance" (m).
EIRP is the effective isotropic radiated power for each antenna (W).
"L" is the Safety Code 6 limit in a specific frequency band (W/m2).
"Rf" is the distance from the reference point that marks the beginning of the far fields (m).
126.96.36.199 Draw a square centered about the reference point, using twice the maximum grid distance as the grid's dimension. Divide this square into a grid comprising of smaller squares whose dimensions are based on the wavelength associated with the site's operating frequency. However, for practical measurements 1.0 m by 1.0 m squares will suffice.
3.2.2 Estimate the power density at each point on the grid.
The power density of each point on the grid can be calculated using RaPD Tool or any appropriate formula.
3.2.3 Select the points to be measured points that are 50% or more of the Safety Code 6 exposure limit as points to be measured at the site and plot them on the grid. For those points less than 50% of the Safety Code 6 limit, no measurement need be taken. When arriving at the site, additional points should be measured in publicly accessible areas (including roof top of buildings where maintenance work may be required) and areas of potential re-radiating RF energy.
3.3 Equipment Selection and Verification
3.3.1 Select equipment with the following characteristics:
- covers the operating frequency range to be measured;
- operates in a high RF field strength environment; and
- operates in the climate and weather condition of the survey locations.
The surveyor should have good knowledge of the equipment and probe (e.g. polarization, behaviour, orientation and the rotation needed to obtain maximum and minimum readings).
3.3.2 Verify that the equipment is calibrated and working correctly. Record the calibration date, the serial number, manufacturer and model of the equipment being used. If the meter is battery operated, ensure that it is fully charged.
3.4 Record Sheet
Set up a recording table, corresponding to the grid, of all points to be measured at the site. There should be at least three columns in the table: the point's relative position, the time the reading was taken, and the reading itself. An area of the sheet should be set up to enter the antenna and transmitter parameters, information regarding the equipment used for the survey, the date, and the weather during the survey. Draw or obtain drawings of the equipment room and test site, noting the relative positions of the antennas, and attach them to the record sheet.
4. Measurement Steps
4.1.1 Calibrate and test the probe to ensure it is functioning correctly before taking any measurements, as recommended by the manufacturer.
4.1.2 Perform a rapid walk around the site with the general probe, set in the maximum hold position, beginning away from the antenna and walking in, moving the probe in a constant up and down, side to side motion. This procedure is to ensure that the surveyor is not at risk of over-exposure. If the readings exceed the RF worker limit, retreat and note the location.
4.1.3 If the equipment room is not located in an area that exceeds the RF worker limit, perform a quick walk around with the general probe to ensure that the room itself is within the RF worker limit. If not, exit the premise immediately and notify the manager.
If the initial readings indicate that the room is within the limits set out in Safety Code 6, check to ensure that there are the same number of transmitters as specified in the preparation calculations. If any of the initial preparation information is contrary to the actual operation setup then recalculate the theoretical estimate with the new data gathered at the site. If all is as expected, continue with the survey.
4.1.4 Verify that the site reflects the description used in the theoretical calculations, by counting the number of antennas, and noting their layout.
4.2 Measurement of RF Energy
4.2.1 Construct the grid and record the locations of any additional points to be measured on the map (e.g. areas that are publicly accessible and of potential radiating of RF energy).
4.2.2 Approach the points of interest within the grid, starting at the point furthest from the antenna or reference point. Moving the probe in a constant up and down, side-to-side motion (at arm's length) at the specific location, note the variation in readings. If there is little variation in the readings, relative to the accuracy of the instrument, then measure the power density at 1.5 m above the floor or ground. Record these values on the record sheet. However if there is a large variation, greater than 110% of the relative accuracy of the instrument, spatial averaging is recommended as per Safety Code 6.
4.2.3 Do not position the body between the antenna and the field probe. Rather position the body so that it is to the side of the antenna-to-field probe axis. This minimizes reflections by the body. Do not take measurements closer than 20 cm from potentially reflective objects.
Note: Presently there are no commercially available H field probes beyond 300 MHz.
4.3 Multiple Sources
Some probes are able to measure all frequencies at once so if this type of probe is used then measure all the sources at once. To ensure that all live transmitters are keyed during the test, turn on one by one, checking at all times that the meter reading has increased, reflecting the addition of each transmitter.
If several probes are needed to cover the entire operating frequency range of the site, attention should be paid so that no transmitter is measured twice. Key each transmitter one by one until all transmitters within the first probe's range have been keyed, checking that the meter reading increases, reflecting the addition of each transmitter. Measure the power density at each point, then, turn off the transmitters. Key the next transmitters (those that have not already been turned on) one by one, that fall into the second probe's range, and measure the power density at each point. Repeat the procedure until all transmitters have been keyed once.
For narrowband receivers, key one transmitter at a time and measure the power density at each point. Repeat this procedure for the remaining transmitters.
5. RF Contact and Induced Currents
For these services, RF contact and induced body currents are not significant. However, it is recommended not to come in direct contact with any metallic surfaces to avoid a shock due to improper grounding.
Include in the report:
- a description of the survey site, transmitting facility and photographs if available;
- any observations regarding the climate, time of day, and anything unusual regarding the site or sources;
- a list of technical parameters of the antennas and transmitters including frequency, power, as mentioned in the initial preparation;
- the equipment used (serial number, and manufacturer) along with the calibration date of the instrumentation, so others can repeat the survey;
- the copies of the site map with each of the tested locations clearly identified and the corresponding readings, highlighting those points in excess of 50% of the safety limit;
- a statement of compliance or non-compliance to Safety Code 6 limits; and
- suggestions where appropriate.
Section B - Procedures for Measuring the Levels of RF Energy Associated with the Portable and Mobile Units of Land Mobile, Cellular and PCS Services
Measurement procedures for the portable and mobile units of Land Mobile, Cellular and PCS Services, please refer to Industry Canada's Radio Standards Specification 102, Issue 2, Radio Frequency Exposure Compliance of Radiocommunication Apparatus (All Frequency Bands) (RSS-102).
1. Measurement Precautions
1.1 Field measurements should be performed only by qualified personnel, who have a good understanding of electromagnetic radiation and radar systems.
1.2 In cases where there is a predicted or known risk of over-exposure to survey personnel, one of four survey approaches may be used depending on the risk assessment;
- For high-risk cases, a horn antenna can be placed inside the measurement area (while the radar transmitter is OFF) and connected to a spectrum analyzer with a low-loss cable of sufficient length to permit data to be taken without risk of overexposure.
- For medium risk cases, survey instrumentation may be placed on a tripod inside the measurement area (while the radar transmitter is OFF) and the meter is read with binoculars or via an optical link.
- For low risk cases, the survey probe may be used for an initial assessment.
- Alternately, where it is not necessary that the transmitter operate at full power, the transmitter may be operated at a reduced power level and the data adjusted to take this power reduction into account.
1.3 Where test procedures require a stationary radar beam. Personnel must be vacated from inhabited areas that will be radiated by, either the main beam, or secondary lobes or reflections from the main beam or secondary lobes.
1.4 For measurements on a scanning/rotating antenna, maintain the position of the survey probe long enough to permit the measurement of several sweeps of the antenna. Ensure that the response time of the survey instrument is fast enough for this type of measurement.
1.5 The radar transmitter shall not be tested without an appropriate load.
1.6 Ensure that there is sufficient clearance between a scanning/rotating antenna and survey personnel to avoid physical injury. Throughout the survey, survey personnel should be in constant communication with the radar operator in order to implement parameter changes required by the test program and to be able to quickly curtail transmitter operation in case of emergency.
1.7 To minimize measurement errors, refer to survey meter manufacturer's guidelines regarding:
- Environmental conditions appropriate for survey meter use (e.g. min/max limits on temperature, humidity and atmospheric pressure to maintain probe accuracy).
- 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).
- Symptoms of survey meter overload and precautions to be taken to avoid overload.
- Uncertainty of measurements taken in the presence of reflecting objects and multiple radiating sources.
1.8 The procedures that follow assume near field conditions and metering capable of indicating 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:
- Health Canada, Limits of Human Exposure to Radiofrequency Electromagnetic Fields in the Frequency Range from 3 kHz to 300 GHz, Safety Code 6, 1999.
- "Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields", Federal Communications Commission/Office of Engineering and Technology, OET Bulletin 65, August 1997.
- "IEEE Recommended Practice for the Measurement of Potentially Hazardous Electromagnetic Fields - RF and Microwave", IEEE STD. C95.3-1991, Institute of Electrical and Electronic Engineers, 1991.
3. Initial Preparation Before Site Visit
3.1 Establish and record the following information relating to the equipment being surveyed:
- equipment manufacturer, model and nomenclature;
- operating frequencies;
- transmit peak power, pulse duration and pulse repetition rate;
- transmitting equipment LO, IF and other frequencies below 300 MHz (for H field measurements);
- transmit antenna gain, beamwidth, antenna orientation (if in fixed position) or rotation angle (less than or equal to 360 degrees) and antenna dimensions;
- intended antenna coverage area (i.e. the area swept by the scanning antenna) and sector blanking (if applicable);
- typical duty cycle or duration of a typical (or worst-case) transmission;
- 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:
- under typical or worst-case equipment operating conditions;
- under the worst-case failure mode;
- at various frequency settings;
- at various transmitter power levels and pulse widths for different modes of operation;
- at fixed or normal antenna scan rates; and
- at maximum transmitter power into the dummy load.
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 current SC6 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 test conditions identified in paragraph 3.2, 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 and/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 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 limits. 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:
- areas in which people may be physically located or pass by in transit;
- general public and RF worker-only areas;
- transmit antenna coverage area and sector blanked area; and
- potential re-radiators of RF energy.
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 The data recording procedures are as described in Section 4 of GL-001.
7.2 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.
7.3 When testing a stationary antenna for a selected radar operating condition, defeat antenna rotation. Then, manually adjust antenna angles such that a worst-case condition is achieved. Otherwise, incorporate the antenna rotational reduction factor into the measurement data as detailed in SC6.
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:
- Approach the radiator by walking in a serpentine motion (i.e. left to right and then back again) across the antenna coverage area.
- 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.
- Use the maximum peak hold feature on the survey meter for a sufficiently long period to ensure that maximum amplitude of the pulses and the sweeps (if the antenna is rotating) have been measured.
- 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.
- Do not survey within 20 cm of any metallic surface or conductor.
- Take into consideration the field strength of the back lobe. Under certain conditions the survey meter could be damaged.
7.5 Survey all areas where people may be physically located or pass by in transit and record the data.
7.6 Survey about all potential re-radiators near where people may be physically located or pass by in transit and record the data.
7.7 Incorporate the antenna rotational reduction factor into the measurement data as detailed in SC6 if MELs are exceeded.
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 spot 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 Repeat the steps described in paragraphs 7.1 to 7.4 for all conditions of interest previously determined in paragraph 3.2.
7.13 Peak electric field strength measurements are only required in the vicinity of electromagnetic pulse (EMP) simulators.
8. Radiation Measurements Around Transmitting Equipment
8.1 The procedures, which 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.
8.2 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.
8.3 The data recording procedures are as described in Section 4 of GL-001.
8.4 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.
8.5 Visually examine all waveguide joints, in areas where personnel may position themselves or position their body extremities, for indications of high voltage arcing. 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.
8.6 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.
8.7 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.
8.8 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.
8.9 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.
8.10 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.
8.11 Compare measurements with previous survey results and investigate any obvious discrepancies.
8.12 Peak electric field strength measurements are only required in the vicinity of EMP simulators.
1. Measurement Uncertainties
Measurement uncertainties are the result of actual measurement uncertainties and/or instrumentation uncertainties.
2. Related Documents
For additional information on measurement uncertainties, refer to Measurement Good Practice Guides by the National Physical Laboratory.
3. Actual Measurement Uncertainties
Actual measurement uncertainties can be minimized by following proper measuring practices and procedures.
4. Instrumentation Uncertainties
Instrumentation uncertainties are primarily due to the design of the instrument. They can also be affected by other factors such as environmental conditions, temperature, humidity, etc. Proper calibration of the instrument can largely eliminate the bias errors and a careful selection of instrument type and measuring method can reduce the value of this uncertainty factor.
4.1 Recommended Procedures for Compliance with Safety Code 6
- The instrument selected must be of recognized commercial type.
- Proper calibration of the instrument must be performed in accordance with the manufacturer's recommended calibration period.
- Provided that correct measurement procedures have been followed and proper calibration of the instrument has been performed, if the measured field strength levels plus the manufacturer's; specified instrument uncertainty factor are below the Safety Code 6 (SC6) limits, these field strength levels will be accepted as measured and the site is deemed to be SC6 compliant.
- If the measured field strength levels plus the manufacturer's specified instrument uncertainty factor exceed the SC6 limits, corrective remedies must be taken to comply with SC6 requirements. Single frequency measurement of all frequencies present at the site can be conducted to improve the instrumentation uncertainty factor.
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