Safety Code 6 (SC6) Measurement Procedures (Uncontrolled Environment)

February 2011 Spectrum Management and Telecommunications Technical Note Safety Code 6 (SC6) Measurement Procedures (Uncontrolled Environment) Aussi disponible en français NT-329

Contents 1.0 Purpose...1 2.0 Introduction...1 3.0 Evaluation Process...1 3.1 FM, Digital Radio, VHF/UHF/Digital TV and MDS Transmitting Sites...2 3.2 AM Transmitting Sites...4 3.3 Microwave Transmitting Sites (Fixed Point-to-Point)...6 3.4 Land Mobile, Cellular, PCS and Microwave Point-to-Multipoint Transmitting Sites...6 3.5 Radar Transmitting Sites...6 4.0 Report...6 References...7 Annex A Flow Chart of the On-site Measurement Procedures...8 Annex B Safety Code 6 (SC6) Limits for Uncontrolled Environments...9 i

List of Acronyms and Abbreviations ALS Assignment and Licensing System AM Amplitude Modulation BCDBS Broadcasting Database CPC Client Procedures Circular E Electric Field FM Frequency Modulation GL Guideline GPS Global Positioning System H Magnetic Field MPE Maximum Permissible Exposure PCS Personal Communications Service PD Power Density RF Radio Frequency SC6 Safety Code 6 TN Technical Note ii

1.0 Purpose The purpose of this technical note is to describe measurement procedures for different types of radiocommunication and broadcasting installations when verifying compliance with the uncontrolled environment limits as set out in SC6. 2.0 Introduction As outlined in CPC-2-0-03, Radiocommunication and Broadcasting Antenna Systems, Industry Canada requires that all radio installations be operated in a manner that complies with Health Canada s Limits of Human Exposure to Radiofrequency Electromagnetic Energy in the Frequency Range from 3 khz to 300 GHz Safety Code 6 (2009) for the purpose of protecting the general public. There are currently various tools, guidelines and documents, developed by Industry Canada, which are available for radio frequency (RF) compliance determination. For instance, Industry Canada has published the GL-01, Guidelines for the Measurement of Radio Frequency Fields at Frequencies from 3 khz to 300 GHz, to verify SC6 compliance. GL-01 covers the measurement procedures for broadcast, microwave, land mobile, paging, cellular, PCS and radar installations. Technical Note TN-261, entitled Safety Code 6 (SC6) Radio Frequency Exposure Compliance Evaluation Template (Uncontrolled Environment Exposure Limits), is an evaluation tool to quickly assess the RF exposure compliance for simple antenna sites using mathematical calculations. HIFIELD is Industry Canada s software for conducting SC6 compliance evaluations for radiocommunication and broadcasting sites. It uses both the radiocommunication database (ALS) and the broadcast database (BCDBS) to select stations within a given area and calculate the exposure levels relative to the uncontrolled environment limits. Calculations may also be done using spreadsheets or other computational modeling software packages that take into consideration near-field and far-field regions, as well as the applicable SC6 limits. This technical note () provides a summary of on-site RF measurement procedures; however, GL-01 and TN-261 should be referenced when specific details are required. 3.0 Evaluation Process To verify SC6 compliance with respect to the uncontrolled environment limits at a specific site(s) of radiocommunication and broadcasting antenna systems, the following steps should be followed: (i) Prior to on-site measurements, an environment search should be performed. All data should be gathered regarding broadcasting stations within a radius of 1 km, and terrestrial fixed transmitter stations in the mobile, cellular, PCS, microwave, radar and radiolocation services within a radius of 100 metres from the specific site(s). 1

(ii) Calculations 1 should be made to estimate RF levels in the far field for the surveyed transmitter site(s) as a way to identify approximate locations to be measured (e.g. locations where calculations show that the RF level is equal or over 50% of the uncontrolled environment limits). Note: If the theoretical analysis reveals no location equal or exceeding 50% of the uncontrolled environment limit (in areas accessible to the general public), the site is considered compliant and no on-site measurement is required. (iii) The far field distance should be considered when selecting the measurement locations. Normally, if a location is in the far field of every radiating element, an E-field measurement is sufficient. Otherwise, both the E-field and H-field should be measured. (iv) Depending on the results of the environment search, narrowband and/or broadband equipment 2 are selected for on-site measurements. (v) (vi) (vii) Using the locations identified in (ii) as starting points, a walkaround survey of the site based on the methodology of GL-01 should be performed to identify points with high RF levels ( 50% of the uncontrolled environment limits, including measurement uncertainty. On-site measurements should be taken with a clear view of the antennas. In the case of rooftop sites, the measurements should be taken, at a minimum, at the locations where a member of the general public could be exposed to the main beam of the antennas. A written record should be kept of the measurement locations, reading levels and logging times. (viii) Measurement uncertainties must be taken into account during the survey. 3.1 FM, Digital Radio, VHF/UHF/Digital TV and MDS Transmitting Sites 3.1.1 Site Characterization The surveyor should initially characterize the transmission site with regard to the temporal variation of the RF signals. To do so, place the survey instrument approximately where the theoretical evaluation showed the strongest level and then use the probe to manually fine-tune the location with the strongest signal within the proximity of the original location. Install the probe on a non-metallic tripod at a height of 1 to 2 metres wherever the signal is stronger. The measurements are logged for a total of 6 minutes in order to evaluate the magnitude of the temporal variations of the signals. If the field signal variations are less than 20% (or power density of 36%), which are normally expected for broadcasting sites, time averaging will not be required for the remainder of the survey (reference: SC6). If the signal variations are more than 20% (or power density of 36%), time averaging over 6 minutes is required for the remaining measurements. Transients in the measurement instrument or electro-static instantaneous sporadic effects can create spikes in the measured RF signal. When determining the signal variation in time, these temporal peaks created by such spikes should not be considered. 1 2 The calculation can be performed using TN-261 and/or HIFIELD (or any commercially available RF software) to determine the location of the maximum RF exposure levels for the site(s) in question. GL-01 provides an overview of the instrument selection when taking RF measurements. 2

3.1.2 Walkaround Once the temporal characterization is completed, the surveyor should walk around the site as described in Section 3.0, with a survey instrument to identify the locations with stronger field exposure, using the results of the theoretical evaluation as a starting point. Normally, this is done by holding the survey instrument away from the body, as the surveyor should not be standing directly in front or behind the survey instrument. There should be no other object located within a few metres of the surveyor. The survey instrument should also be pointing towards the transmitting antenna(s). The height of the survey instrument should be kept between 1 and 2 metres above ground level wherever the signal is stronger. Locations where the RF signal is close to the SC6 limit for uncontrolled environments (e.g. at or above 50% of SC6 uncontrolled environment limits) should be considered for detailed measurements, including temporal and spatial averaging as needed. 3.1.3 Detailed Measurement 3.1.3.1 Time averaging not required If the above characterization of the site reveals that no time averaging measurements are required, a quick scan of the probe over the cross-sectional area equivalent to a human body should be done to determine the spatial averaging value of each measurement location. Normally, a scan of at approximately 30 seconds may be considered provided that the probe has a fast response time. 3.1.3.2 Time averaging required If time averaging measurements are required, each point of a 9-point matrix representing the cross-section of a human body should be logged for 6 minutes, and then averaged. In this case, the probe should be set on a non-metallic tripod for convenience. Figure 1 - Example of a Grid for Measurements of a Non-Uniform Electric Field and the Calculation of the Average Power Density (GP Limit) of 1800 MHz 3

Example 1: The meter has a reading of 5% of SC6 for the controlled environment limits. In terms of the uncontrolled environment limit, the controlled environment level is multiplied by a factor of 5 to give a SC6 value of 25%. If the instrument has an uncertainty of 3 db, the percentage of SC6 could be as high as 50% of the uncontrolled environment limit. Therefore, the location should be considered for detailed measurements. Example 2: The meter has a reading of 2% of SC6 for the controlled environment limits. In terms of the uncontrolled environment limit, the controlled environment level is multiplied by a factor of 5 to give a SC6 value of 10%. If the instrument has an uncertainty of 3 db, the percentage of SC6 could be as high as 20% of the uncontrolled environment limit. Therefore, the location does not need to be considered for detailed measurements. 3.1.4 Induced and Contact Current Measurements With regard to induced and contact currents, measurement considerations are required if transmitters within the environment in question have operating frequencies of 110 MHz or below. Under certain conditions, the induced current can exceed the limits specified in Table 2 of Annex B, even though the electric field strengths are below the limits specified in Table 1 of Annex B. These conditions may occur when the electric field strength is as low as 25% of the exposure limit. Therefore, induced current through both feet can be measured by using a clamp-on current probe or a low-profile platform consisting of two parallel conductive plates isolated from each other and one located above the other when the electric field is 25% of the uncontrolled environment limits or higher. The initial induced current measurements should be made at the locations with the highest field strengths. Similarly, the contact current can exceed the current limits specified in Table 2 of Annex B, even though the electric field strengths, which are the major contributor to the contact current, are below the limits as specified in Table 1 of Annex B. These conditions may occur when the electric field strength is as low as 25% of the exposure limit. For any conducting metallic object that a person may come in contact with and that is located in a high-intensity RF field, contact currents should be measured when the electric field is 25% of the uncontrolled environment limits or higher. An electric circuit having the impedance of the human body or a clamp-on current probe should be used for measurements. 3.2 AM Transmitting Sites Due to the distances between the radiators (towers) in AM arrays, each tower must be assessed separately. Alternatively, for each tower, a practical radial distance can be established, where measurement can begin and proceed towards the tower (see Table 1 below). 4

Table 1: Location Prediction of Exposure Contours for AM Antenna Systems 3 Electric Field Strength (V/m) Magnetic Field Strength (A/m) Tower Base Input Power (kw) 50 25 10 5 2.5 1.0 0.5 0.25 0.10 25 0.06 109 83 60 47 37 27 22 18 13 50 0.13 65 51 37 29 23 18 14 11 8 75 0.19 49 38 28 23 18 13 11 8 6 100 0.25 40 31 23 19 15 11 9 7 5 150 0.38 30 24 18 15 11 8 6 5 4 200 0.50 25 20 15 12 9 7 5 4 3 280 0.74 21 17 12 10 7 5 4 3 2 300 0.75 20 16 11 9 7 5 4 3 < 2 400 1.00 16 13 9 7 6 4 3 < 2 < 2 500 1.25 14 11 8 6 5 3 3 < 2 < 2 750 1.88 11 8 6 5 4 3 < 2 < 2 < 2 1000 2.50 9 7 5 4 3 < 2 < 2 < 2 < 2 Note: Distance (in metres) at which fields from AM antenna systems are predicted to fall below various field strength levels (from the Federal Communications Commission OET Bulletin 65 4 ). In-between distances can be estimated by linear interpolation of the two closest listed distances. If the Table method is used, the measurement zone for each tower should be determined using the relevant input power at its base. While this is only an approximate method, it is sufficiently accurate in most cases. When in doubt, a minimum measurement radius of 5 metres is suggested for low-power towers. The SC6 uncontrolled environment limits will be found to lie along a locus generally circular or slightly egg-shaped around the foot of each tower. For a detailed measurement, a minimum of four (4) readings should be taken along each radial for each tower, moving inwards from the maximum measurement radius. In general, only the hottest tower (i.e. the one with the most current) needs to be considered. The calculated measurement radius may have to be extended if readings at the starting point already exceed the recommended SC6 uncontrolled environment limits. Section 3.1 should be referenced for the measurement steps. However, because RF measurements for AM stations are typically taken in the near-field region, both electric and magnetic fields should be measured when taking detailed measurements. Both induced and contact current measurements should be taken. 3 4 This table can be used for all AM frequencies and tower heights. The entries in this table apply to both electric field strength and the corresponding magnetic field strength (assuming a free-space impedance equal to 377 W). Federal Communications Commission (FCC) OET65 (http://www.fcc.gov/oet/info/documents/bulletins/) 5

3.3 Microwave Transmitting Sites (Fixed Point-to-Point) When field strength measurements are required for microwave transmitting sites, the following considerations are applicable: If the radiator is not highly directional (i.e. beamwidth > 5 degrees), assume that far-field conditions exist beyond a one-metre distance for frequencies above 300 MHz. If it is estimated that far-field conditions exist, SC6 permits the measurement of E, H or Power Density (PD). If it is estimated that near-field conditions exist, SC6 requires separate E and H measurements within the operating range of commercially available survey instrumentation. However, if it is unknown whether near-field or far-field conditions exist, then assume that near-field conditions and separately measure both E and H. The measurement procedures for determining RF values described in Section 3.1 should be followed for microwave transmitting sites, including the induced and contact current measurements. 3.4 Land Mobile, Cellular, PCS and Microwave Point-to-Multipoint Transmitting Sites Transmitting facilities involving land mobile, paging, two-way, trunking, cellular and PCS services are operating in the frequency range of 30 MHz to 2 GHz. The measurement procedures for determining RF values described in Section 3.1 should be followed for these types of sites. In the case of induced and contact current, measurements considerations are required if transmitters within the environment in question have operating frequencies of 110 MHz or below. 3.5 Radar Transmitting Sites For radar transmitting sites, pay special attention to temporal averaging over 6 minutes. A detailed methodology for this type of installation will be described in a subsequent issue of this technical note. In the meantime, the procedure describe in GL-01 should be followed. Induced and contact current measurements are not required for these installations. 4.0 Report GL-08, Guidelines for the Preparation of Radio Frequency (RF) Exposure Compliance Reports for Radiocommunication and Broadcasting Antenna Systems, should be used when reporting the RF exposure measurement survey. 6

References (1) GL-01, Guidelines for the Measurement of Radio Frequency Fields at Frequencies from 3 khz to 300 GHz (2) GL-08, Guidelines for the Preparation of Radio Frequency (RF) Exposure Compliance Reports for Radiocommunication and Broadcasting Antenna Systems (3) TN-261, Safety Code 6 (SC6) Radio Frequency Exposure Compliance Evaluation Template (Uncontrolled Environment Exposure Limits) (4) Health Canada s Limits of Human Exposure to Radiofrequency Electromagnetic Energy in the Frequency Range from 3 khz to 300 GHz Safety Code 6 (2009) (5) IEEE C95.3, Recommended Practice for Measurements and Computations of Radio Frequency Electromagnetic Fields with Respect to Human Exposure to Such Fields, 100 khz-300 GHz, 2003 7

Annex A Flow Chart of the On-site Measurement Procedures Environment Search Selection of equipment (i.e. broadband or narrowband). Calculation to estimate SC6 levels and contours. Determination of the approximative locations where levels are at or exceed 50%* of the uncontrolled environment limit. Position the survey instrument at the location with highest predicted level. Fine-tune the location and probe height for the signal in proximity. Characterize the temporal variation of the site by measuring field strength with probe on tripod for 6 minutes. Temporal averaging required if field variation over 20%. Location with high levels (at or over 50%* of SC6 uncontrolled environment limits) found by walkaround with probe between 1-2 m. No Yes Calculate a 9-point spatial averaging with 6 minutes time averaging for each point. Yes Temporal averaging required? No Calculate a spatialaveraging over the cross section of a human body for a minimum of 30 seconds. Yes E-field > 25% of SC6 limit? Yes Operating frequency 110 MHz and below? No Contact and induced current measurement required. No * Includes measurement uncertainties. Write report or keep records. 8

Annex B Safety Code 6 (SC6) Limits for Uncontrolled Environments Table 1: Field Strength/Power Density Limits for the Uncontrolled Environment Electric Field Strength (V/M rms) Magnetic Field Strength (A/m rms) Time Averaging (minutes) Frequency Range Power Density (W/m2) 0.003-1 MHz 280 2.19-6 1 10 MHz 280 / f 2.19 / f - 6 10 30 MHz 28 2.19 / f - 6 30 300 MHz 28 0.073 2 6 300 1500 MHz 1.585f 0.5 0.0042f 0.5 f/150 6 1500-15000 MHz 61.4 0.163 10 6 15000 150000 MHz 61.4 0.163 10 616000/f 1.2 150000 300000 MHz 0.158f 0.5 4.21 x 10-4 f 0.5 6.67 x 10-5 f 616000/f 1.2 Table 2: Induced and Contact Current Limits for the Uncontrolled Environment RMS Induced Current (ma) RMS Contact Frequency Range Through Current (ma) Time (MHz) Hand Grip Averaging Both Feet Each Foot and Through Each Foot 0.003 0.1 900 f 450 f 450 f 1 s 0.1 110 90 45 45 6 min 9