27581 San Diego Gas And

SUPPLEMENTAL INFORMATION

San Diego Gas and Electric Company

File No. 0103-EX-PL-2015 Reference No.: 27581

San Diego Gas and Electric Company (“SDG&E” or “Company”) requested an experimental authorization that would allow it to deploy 449 MHz Radar Wind Profilers (“RWPs”) at two sites in Southern California. As the Company explained in its application, the data obtained from the RWPs is essential to SDG&E’s research in modeling atmospheric characteristics that are expected to be significant in predicting wind conditions that contribute to dangerous fire activity. The application was supported by the National Weather Service (“NWS”), which explained that SDG&E would contribute to the NWS research by collecting data beyond surface data, specifically “critical wind data from multiple levels of the atmosphere.” The NWS also stated that, “These data will add tremendous value to our numerical weather modeling efforts….”

The objective of this research into wind condition prediction is better protection of safety of life and property in Southern California. Timely and accurate forecasts of Santa Ana winds are critically important to SDG&E's emergency preparedness activities. The Company is all too aware that sparks from overhead power lines and other electrical equipment can result in large and destructive wildfires. It is anticipated that the data collected from atmospheric profilers, including 449 MHz RWPs, during Santa Ana wind events will improve the weather forecast models upon which SDG&E and others rely to prepare for these potentially catastrophic fire-weather events. (See Attachment A). Further, while the Company cannot say with absolute certainty what data will be obtained from its experimental operation of a 449 MHz RWP, it will be shared with other stakeholders in the meteorological community to ensure greater public awareness and safety during periods of dangerous fire-weather conditions. The following is a list of stakeholders with whom the Company will share this data:

1) The National Weather Service (NWS) Weather Forecast Office (WFO) in San Diego, CA a. Supports aviation forecasts, fire weather forecasts and warnings, and severe weather forecasts and warnings. b. Data may be leveraged by Incident Meteorologists (IMET) responsible for providing weather support during major incidents, including wildfire and HAZMAT disasters.

2) Los Angeles Center Weather Service Unit (ZLA) a. Supports the issuance of Center Weather Advisories to private pilots, control towers, flight service stations, and commercial airlines in the greater Southern California area.

3) The Southern California Geographic Area Coordination Center’s (GACC South Ops) Predictive Services group. a. Supports daily fire potential forecasts which, in turn, support firefighter resource allocation across multiple fire agencies in Southern California.

4) The San Diego County Air Pollution Control District a. Supports air quality forecasts for San Diego County.

5) The Navy Fleet Weather Center at Naval Air Station North Island a. Supports forecasts for weather-sensitive Navy operations.

6) UCSD Department of Mechanical & Aerospace Engineering a. Data may be used to make improvements to weather forecast models. b. Supports the development and improvement of renewable energy forecasts.

SDG&E also has given further consideration to the locations it had proposed for deployment of its 449 MHz RWPs. It recognizes that the requested site in San Clemente has raised concerns about whether its proximity to San Diego might permit interference to Remote Pickup Broadcast and/or amateur operations in that area. Experience with even higher-power 449 MHz RWPs in other markets of at least equivalent population suggests that interference would not be an issue. Nonetheless, the Company has determined that its research efforts can be satisfied with data collected from the proposed Borrego Springs location and will modify its application to delete the San Clemente site.

The Borrego Springs site is approximately 61 miles/99 kms from the center of San Diego. It is in an area that would qualify as rural and very lightly populated by any standard. Moreover, as shown on Attachment B (Figures 4-8), the site sits in a basin surrounded by mountainous terrain. There is substantial shielding between this location and population centers in the area, including San Diego.

In addition to the natural topographic protection provided by the site and its remote location, the Company is confident that the RWP it will be using has been designed to further mitigate any potential for interference. Attachment B describes in detail the configuration of the equipment it will be using, including the side lobe attenuation, filtering, clutter fence and other features that enable this RWP to be a compatible neighbor to other spectrum users.

SDG&E recognizes the obligations to which it would be subject should the FCC grant this experimental application. It would operate on a secondary basis to licensees of primary authorizations and would be obligated to cease operation immediately should it cause interference to their transmissions. For all the reasons described in Attachment B, SDG&E is confident that deployment of the Raptor XBS-T at that site presents no real possibility of interference to other entities, but it remains committed to full cooperation with protected licensees and with the FCC should an issue arise.

ATTACHMENT A SDG&E Radar Wind Profiler (RWP) Research Efforts:

Steve Vanderburg Senior Meteorologist, Electric Distribution Operations San Diego Gas & Electric August 3, 2015

Overview: Santa Ana winds are associated with many of the largest, most destructive wildfires in our region’s history. For years, it was thought that the strongest winds occurred where air was funneled through passes and canyons. However, recent observations from our service territory indicate otherwise. We have since learned that Santa Ana winds are analogous to rapids in a river, though much more research is needed to better understand this phenomenon. As part of our research efforts, SDG&E has acquired two atmospheric profilers to be used in tandem to obtain vertical profiles of wind and stability on both the windward and leeward side of the mountains during Santa Ana wind events. We hope this data will enable us to better predict the severity and extent of strong winds during Santa Ana wind events.

915 MHz RWP: The data we collect from the 915 MHz RWP will be used to relate wind gusts as measured by the SDG&E mesonet to the vertical profiles of wind and stability (up to 2 km in height) within the downslope portion of the wave (coastal side of the mountains). See image above. This will hopefully lead to the creation of skillful wind gust parameterizations for various Numerical Weather Prediction (NWP) models such as the Weather Research and Forecasting (WRF) model.

449 MHz RWP: The data we collect from the 449 MHz RWP will be used to relate upstream vertical profiles of wind and stability (up to 5 km in height) to the resultant mountain wave activity (severity and extent of the winds) on the downstream side of the mountains. See image above. This will hopefully lead to the creation of semi-idealized models that predict how Santa Ana winds will behave in response to subtle changes in upstream conditions. A 915 MHz RWP does not have the vertical range necessary to meet these requirements.

This photograph is an example of stable air spilling over terrain and into a hydraulic jump. Santa Ana winds behave in a similar way but are much stronger and occur under clear skies with very low humidity.

High-resolution model cross-section of Santa Ana winds in San Diego County. The 915 MHz RWP is located near point A and the 449 MHz RWP would be located in Borrego near point B.

ATTACHMENT B 1022 West 23rd Street, Suite 620, Panama City, Florida 32401 USA Tel 850.763.7200 117 South Sunset St. Suite L, Longmont Colorado 80501 USA Tel 303.848.8090 Web www.detect-inc.com

Aircraft Birdstrike Avoidance Radars – Wind Energy Avian Radar Systems – Security Radar Systems – Radar Wind Profilers

Attachment B, SDG&E 449-MHz Radar Wind Profiler Experimental Application

RAPTOR XBS-T, Inherent Interference Mitigation Attributes

1 Introduction San Diego Gas and Electric (SDG&E) has applied for an experimental frequency license to test the effectiveness and operations of a DeTect, Inc. (DeTect) RAPTOR XBS-T (XBS-T) Radar Wind Profiler (RWP) for support of Santa Ana Winds research and use in wildfire support. As an adjunct to SDG&E’s application, this document contains relevant information about the XBS-T operations that pertain directly to its ability to mitigate inference to and from other RF systems.

The following treatment is divided into:

1) Technical information about the model RAPTOR XBS-T,

2) Information related to the site-specific operations in Borrego Springs, California, and

3) General information regarding radar wind profiler operations.

The essential points of this document are that modern 449.0 MHz horizontally-polarized wind profiler radar radiates minimal interference power through low elevation sidelobes into adjacent bands; a sidelobe-reduction clutter fence is integral to the XBS-T; and any residual energy will be effectively contained within the Borrego Valley by terrain.

2 RAPTOR XBS-T Built-In Interference Mitigation The following subsections describe specific attributes of the XBS-T radar wind profiler that mitigate interference to other systems. The important attributes are amplitude tapering and clutter fencing to minimize low-elevation angle ERP, pulse filtering to minimize necessary bandwidth, and transmitter linearity and transmitter protection to minimize spurious products. Figure 1 shows the complete XBS-T system, including the electronics trailer and the antenna trailer. Table 1 gives system specifications.

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The information contained and/or attached to this document is for the intended recipient only and may not be distributed to third parties in any form without the express written consent of the DeTect, Inc. This communication contains confidential, proprietary and/or privileged information that is protected by U.S., U.K. and International law and, the recipient hereby agrees to treat it as such. If you have received this in error, immediately and permanently destroy or delete this document and all enclosures or attachments. ANNEX: SDG&E / RWP Inferference Mitigation August 5, 2015

Figure 1. RAPTOR XBS-T showing both the electronics and antenna trailers.

Table 1: RAPTOR XBS-T Specifications

Item Value Note Transmitter Frequency 449.0 MHz Fixed, crystal oscillator Tolerance 10 ppm Bandwidth B(-20) 2 MHz Necessary bandwidth Type Solid-state Ultra-linear, protected by two ferrite circulators Transistor Peak Power (Tx out) 1.5 kW Transmitter capable of 2kW average power Average Power (Tx out) 55 W Transmitter capable of 300W average power Harmonic Filter Cavity Installed after immediately before the antenna to reduce harmonic content Antenna Type Planar Phased Array Diameter 14’ Beamwidth (-3 dB) 10˚ vertical, 11˚ oblique Gain ~ 25 dBi Element Type Yagi-Uda element Metal ground plane acts as director for element No. of Radiating Elements 73 Hexagonal spacing Amplitude Tapering ~25 dB Taylor Uneven RF power dividers deliver controlled amplitude to each Yagi-Uda element Pointing Method Solid-state phase Uses PIN diode (non-wearing) phase-delay shifters

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Number of Beams 1 vertical, 6 Oblique beams point at 67˚ above horizon oblique Clutter Fence Metal Screen, 40” Integral with antenna platform tall ERP (peak power) of main beam 360 kW In-band ERP (average power) of main 38 kW In-band beam ERP (peak power), low-elevation- 30 W In-band, assuming -15 dBi SLL angle sidelobes ERP (average power), low- 1 W In-band, assuming -15 dBi SLL elevation-angle sidelobes Transceiver Pulse Width 6.7 uS Total tapered pulse group duration IPP 96 uS aka PRT Pulse Modulation Bi-phase (180˚) Typical 1, 4, or 8 chips in pulse group Pulse Shaping Tapered rise & fall To reduce bandwidth, phase changes go to zero Oscillator Oven controlled

2.1 Antenna Design and Pattern As noted in the general information section about radar wind profiler operations (below) , radar wind profilers use a vertically directed main beam, so the main concern for interference is the horizontal (low elevation angle) sidelobes. The XBS-T uses several techniques to control sidelobes, including a hexagonal layout for the elements, element-to-element spacing to create null at horizon, amplitude tapering of the element feed network, and a built-in clutter fence. The Yagi-Uda elements also have a natural null at the horizon (when pointed straight up). Figure 2 shows a close-up of the Yagi-Uda antenna array and the built-in clutter fence. Figure 3 shows the calculated beam pattern for the system.

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Figure 2. RAPTOR XBS-T antenna showing Yagi-Uda elements and clutter fence.

Figure 3. RAPTOR XBS-T calculated antenna patterns for an oblique (off-vertical) beam.

2.2 Transmitted Pulses

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The XBS-T uses a software defined radio (SDR) card which digitally generates the transmit signal and digitally samples the receive signal. The XBS-T transmitted pulses’ length and shape are designed to minimize necessary bandwidth and allow operations within the NTIA Redbook, Section 5.5, Radar Spectrum Engineering Criteria (RSEC), Group E. The term RSEC-E identifies the spectrally efficient criteria intended for federal wind profiler radars operating at 449.0 MHz. Key RSEC-E criteria are listed in Table 2, and XBS-T pulse modes are described in Table 3. These are tighter than the parameters considered as Type A or Type B in NTIA 91-280. Pulse mode LM is the most commonly used pulse mode for lower-tropospheric monitoring.

Table 2: NTIA RSEC-E Key Emissions Criteria

Item Value Note Transmitter Center Frequency 449.0 MHz Wind Profiler Radar (WPR) operating on 449 MHz Tolerance 10 ppm Bandwidth B(-3) < 1 MHz Bandwidth B(-20) 2 MHz EIRP Main Beam 110 dBm Main beam elevation angle must remain greater than 70 degrees; Maximum maximum EIRP is used for upper tropospheric (NTIA Type A) wind profiler radars. EIRP Horizontal Sidelobe 70 dBm for elevation angle < 5 deg Maximum EIRP Horizontal Sidelobe 58 dBm for elevation angle < 5 deg Median

Table 3: RAPTOR XBS-T Pulse Characteristics

Item Value Note Mode LLM LM Rise and fall time tr, tf 0.35 uS 0.45 uS 10% to 90%, ref NTIA Redbook, Annex J Chip pulsewidth t 0.72 uS 0.85 uS 50%, ref NTIA Redbook, Annex J Chip overall duration 1.4 uS 1.68 uS Number of chips 1 4 Biphase modulated within multi-chip pulse groups Interpulse Period IPP 58 uS 96 uS Eff Duty Ratio DR 1.24 % 3.54 %

3 Site-Specific Analysis (Borrego Springs, CA)

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This section addresses potential radiofrequency interference (RFI) to adjacent services such as amateur radio service and broadcast service (particularly remote pickup units or RPUs) from wind profiler radars operating at 449.0 MHz.

The NTIA issued a report in September 1991 (NTIA 91-280) titled Assessment of Bands for Wind Profiler Accommodation to address the need for spectrum for this service. An NTIA Letter from Richard Parlow, Associate Administrator, OSM to Dr. Thomas Stanley, Chief, OET dated January 17, 1992, proposed an amendment to 2.106 of the rules to allocate 2 MHz of spectrum to wind profiler radars. This letter included supporting technical information plus Enclosure 2 "EMC analysis between Type A wind profilers and remote pickup broadcast stations”. A concern about RF interference followed from this enclosure, and from the NTIA Report 21-280 titled Assessment of Bands for Wind Profiler Accommodation. Subsequently, the FCC RM-8092 (ET Docket 93-59), issued March 10, 1993, addressed the needs for wind profiling and contained further technical summary.

In NTIA Report 91-280 the authors employed a generic application of frequency dependent rejection (FDR) and frequency-distance (F-D) curves to assess potential interference among various services and wind profiler radars. This section contains an updated interference analysis, revised according to field experience, best design practices, improved components, and specific interference geometry and interference coupling mechanism.

The Radar Spectrum Engineering Criteria for Group E wind profiler radars at 449.0 MHz RSEC-E was not promulgated until late 1993. The significance of RSEC-E was not recognized outside federal groups and apparently had little impact on the discussion of adjacent band interference following RM-8092. This engineering criteria specifies strict control of sidelobe levels, inband emissions (necessary bandwidth 2.0 MHz), and out-of-band spectral levels for these vertically- pointing research or operational meteorological radars to operate in an adjacent band to other services. The XBS-T is a well-designed, well-built, well-tested wind profiler radar conforming to RSEC-E and suitable for operating even in more populated areas.

The following interference discussion is divided into three parts.

A general description of the proposed SDG&E siting area near Borrego Springs, CA is presented first.

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Second, terrain propagation model results are presented that identify the interference performance of the XBS-T against a distant repeater, representative of an adjacent-channel interference situation that arises in practice. Not every possible combination of frequency offsets and geometries is shown, but the results under this heading give an intuitive appreciation for the interference likelihood, especially of the RPU geometry. The model results corroborate field experience: no harmful or destructive interference from 449.0 MHz wind profiler radars has been reported to DeTect, Inc. during years of Type A prototype operation in a semi-urban area, nor have interference complaints been reported to our knowledge from the many federal 449.0 MHz wind profiling radars operating in many situations for many years.

Third, the application of frequency-distance curves (such as contained within Report 91-280) are briefly discussed relative to updated technical parameters. FDR is the product of two factors on-tune rejection (OTR) and off-frequency rejection (OFR) in dB.

FDR (Δf) = OFR (Δf) + OTR

Where FDR is the rejection provided by a receiver to a transmitted signal as a result of both the limited bandwidth of the receiver with respect to the emission spectrum and the specified detuning, OTR is the rejection provided by a receiver selectivity characteristic to a co-tuned transmitter as a result of a modulated emissions spectrum exceeding the receiver bandwidth. OFR is the additional rejection, caused by specified detuning of the receiver with respect to the transmitter.

3.1 Borrego Valley Terrain Borrego Springs is small village in eastern San Diego County located on the floor of the Borrego Valley, at the westernmost extent of the Sonoran Desert. Average maximum/minimum January temperatures are 20.7 °C / 6.7 °C. Average July maximum/minimum temperatures are 41.8 °C / 24.3 °C. Average annual precipitation is 5.81 inches and altitude 182 m AMSL. Surrounding mountains produce an isolated radiofrequency environment around Borrego Springs.

The Borrego Valley can be identified as the mountain-surrounded valley, centered in the map of Figure 4. Note that metropolitan San Diego lies over intervening mountain ranges to the southwest, and the Salton Sea and Imperial Valley lie over mountains to the east.

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Figure 4. This map illustrates a portion of San Diego County, approximately 267 km east-west by 150 km north-south, centered on Borrego Springs; the icon is marked at the proposed SDG&E site.

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Figure 5. Google Earth satellite image of Borrego Springs, CA.

3.2 Irregular Terrain Radio Propagation Using the software program Radio Mobile we evaluated the interference potential of an experimental wind profiler radar sited near Borrego Springs. This software is a commonly-used amateur radio propagation prediction vehicle that in turn employs the NTIA/ITS Longley-Rice algorithm for irregular terrain and a free-space calculation for non-obstructed paths.

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Figure 6. The same portion of San Diego County centered on the Borrego Valley showing terrain only, and suggesting a measure of radiofrequency isolation.

Longley-Rice, the ITS irregular terrain model, is a general-purpose statistical radio propagation model, based on electromagnetic theory and on statistical analyses of both terrain features and radio measurements. It predicts the median attenuation of a radio signal as a function of distance and the variability of the signal in time and in space. The model is employed in this form to make "area predictions" for such applications such network design, military tactical situations and surveillance, and land-mobile systems.

Longley-Rice model parameters are listed in Table 4, beside pertinent auxiliary transmitter and receiver characteristics. Roads and landform annotation will be omitted from radio propagation plots below for readability.

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Table 4: Propagation parameters for XBS-T sidelobe emissions

Item Value Note XBS-T Propagation-relevant Parameters ERP thru low-elevation- 1 W/0.35 W For pulse modes LM/LLM, in-band emissions, assuming -15 dBi angle sidelobes SLL OTR -17 dB/ -15 dB For pulse mode LM/LLM the PSD ratios are roughly 800 kHz/1000 kHz transmit to a 30 kHz receiver bandpass ratios OFR (Δf) -20, -34, -54 Pulse Mode LM For OFR (Δf) = 1 MHz, 1.5 MHz, and 4 MHz (as dBc measured) OFR (Δf) -20, -23, -52 Pulse mode LLM For OFR (Δf) = 1 MHz, 1.5 MHz, and 4 MHz (as dBc measured) FDR (Δf) = OFR (Δf) + OTR -36 dBc or less Minimum FDR occurs just off-band (at Δf = 1 MHz) increasing with Δf XBS-T polarization H L-R 90/50/50 % Longley-Rice parameters Time/Location/Situations Surface refractivity 301 N Ground conductivity 0.001 S/m Poor ground Ground relative 4 Poor ground permeability Climate Desert Toro Peak Pt 15 W Remote transmit power Toro Peak Gt 6 dBi Remote transmit antenna gain Toro Peak Ht 3 m Remote transmit antenna height Toro Peak Polarization V Remote transmit antenna polarization Received power display -120 to -30 dB Received power of -120 dBm or 0.22 uV through a unity gain 50 scale ohm system antenna roughly equates to 10.3 dBuV/m Polarization V Model polarization Cross-polarization loss -3 to -10 dB Typical for field conditions EIRP low-elevation-angle 0.0003 For pulse modes LM/LLM , off-band (Δf = 1 MHz), including sidelobes W/0.00004 W cross-polarization loss

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Table 5. Converting XBS-T radiated power from a peak power transmitter specification to an adjacent channel low-elevation-angle sidelobe power for LM and LLM pulse modes. These EIRPs were used for propagation estimates.

Figure 7. Very low radiated adjacent channel power at 450.1 MHz (an offset frequency of 1.1 MHz), a small blue area surrounding the SDG&E Borrego Springs location, modeled from the XBS-T parameters

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for pulse mode LM as received by a 25 kHz sensitive receiver with unity gain antenna; the received power colors cover from a lower threshold at -120 dBm/30 kHz to a maximum of -30 dBm/30 kHz.

Figure 8. 450 MHz band coverage from a Toro Peak transmitter as received by a 25 KHz sensitive receiver with unity gain antenna; the received power color scale covers from a threshold at -120 dBm/30 kHz to -30 dBm/30 kHz. This map is intended to represent a system downlink.

In San Diego County the 70 cm amateur repeater receivers are tuned 5 MHz below the assigned transmit frequency: repeater input band 442.0 MHz - 445.0 MHz, and repeater output band 447.0 MHz - 450.0 MHz. Consequently a repeater receiver will have a minimum 4 MHz offset from the wind profiler radar assignment at 449.0 MHz. As an example, the repeater on Toro Peak (approximately 30 km north of Borrego Springs) may be the dominant 70 cm server for the Borrego Valley. From a recent listing, its output frequencies are 446.580, 449.620, and 449.780 MHz.

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Figure 9. Radio path parameters of interest from Toro Peak to Borrego Valley corresponding to the coverage map of Figure 8.

The terrain profile and downlink power estimates from Toro Peak to Borrego Springs are given in Figure 9. The repeater receiver is at 5 MHz lower (uplink). A similar geometric configuration of adjacent channel remote receiver occurs with broadcast service RPU receivers located a separation distance at a broadcasting access point of presence (POP) location.

Figure 10 depicts an example of the spatial distribution of adjacent channel downlink interference produced by the wind profiler radar at a worst-case carrier offset frequency of 1.1 MHz from the wind profiler (worse than the 4 MHz frequency offset of the amateur repeater, which, at a minimum 4 MHz offset, retains a much lower mutual interference probability). In Figure 10, the small areas of server reduction are caused by either terrain shadowing of the primary server or by proximity to the wind profiler radar. These propagation results would apply to broadcast services RPUs operating with similar geometry.

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A field check conducted several years ago with an amateur handheld transceiver suggested that the onset of harmful interference/overload was observed only within a proximity of roughly 150 meters from a Type A (defined in NTIA 91-280) wind profiler radar.

Figure 10. Predicted Toro Peak adjacent channel downlink degradation from an XBS-T located near Borrego Springs. The red shading was applied at locations of less than 12 dB S/I criteria, assuming again a 25 KHz sensitive receiver with unity gain antenna. This plot follows from Figures 7, 8, and 9.

The above propagation plots depict the potential out of band interference (at Δf = 1.1 MHz from the wind profiler carrier assignment, generally a worst-case adjacent spectrum condition). Radio amateur repeaters receivers at 4 MHz offset would experience an additional 30 dB reduction of any residual sidelobe emission from the radar. Further, since XBS-T sidelobe levels vary somewhat in azimuth, it is possible to coordinate rotational antenna pattern adjustment with local frequency coordinators in the event that a minimal interference condition arises.

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3.3 Frequency-Distance The frequency management process often begins with predicted frequency-distance (F-D) separations based on simple propagation and on preliminary transmit parameters and receiver parameters. This preliminary analysis provides an indication any possibility of mutual interference. The process then advances through steps based on the technical context of the specific radio services. Further analysis tailors the F-D for system sensitivity, modulation, and antenna properties of modern equipment. The F-D analysis must be confirmed by data obtained under representative operating conditions to establish a practice. For some ground- based technologies F-D rules have been extensively tailored, for example television transmitting sites operating to home receivers. New technologies raise the question what kind of F-D tailoring a spectrum manager should apply when new and old systems occupy adjacent frequency bands? In the case at hand, the anecdotal field experience with years of 449.0 MHz wind profiler operation suggests that the location of FM services in adjacent bands may have been a beneficial selection. Recalculating F-D curves of the NTIA 91-280 report using realistic transmit parameters which following RSEC-E noticeably reduces the required F-D separations. Further, employing realistic terrain further reduces the separation distance required against thermal noise.

4 Radar Wind Profiler Operations Radar wind profilers are vertically-pointing pulse Doppler radars, which use backscattered reflections from clear-air turbulence to calculate profiles of wind. In some respects, they operate similar to Doppler weather radar, but use lower frequencies and a vertical beam, and much simpler beam pointing strategy.

Radar wind profilers are most used for pollution studies, test range support, atmospheric research, aviation support and weather forecasting. Radar wind profilers of the same type are usually not located any closer than 100 to 200 miles. For example, the NOAA Profiler Network used over 30 profilers to aid in severe storms research and forecasting across the mid-west of the U.S. In that case, the profilers were widely separated and all were located in rural areas. These systems originally operated at 404 MHz, but were scheduled for transition to 449 MHz (this program was recently cancelled due to budget cuts by the NWS). Figure 11 shows the location of the original NOAA profilers (from http://www.profiler.noaa.gov/npn/npnSiteMap.jsp).

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Figure 11. NOAA Profiler Network site location.

Similarly, there are various non-NOAA wind profilers operating in the continental US. Data from these systems is gathered by a NOAA sponsored website called Cooperative Agency Profilers (CAP, https://madis-data.noaa.gov/cap/profiler.jsp). The CAP site allows other user of wind profiler data to access data from these systems. Figure 12 shows disparate locations of the cooperative agency profilers.

Figure 12. Location of CAPs radar wind profilers (mixed sites of 449 MHz and 915 MHz).

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4.1 Vertically Pointing Main Beam, Sidelobes and Clutter Fences RWPs use a simple technique termed Doppler Beam Swinging (DBS) for their beam pointing strategy. DBS means that the main beam is pointed in a limited number of directions (3-6) directly above the radar, in order to measure radial Doppler shift vertically and in the horizontal Cartesian plane. Typically the elevation angle is 70-75 degrees above the horizon and in fixed azimuth directions separated by 60 - 90 degrees. Figure 13 shows a typical configuration.

Figure 13. Beam configuration of a typical DBS radar wind profiler (image from ECC, 2006).

By itself, vertical pointing of the main beam (versus horizontal) creates a significant reduction of interference potential since the main beam is essentially directed to outer space. Typical horizontal (low elevation angle) sidelobes are on the order of 40 to 50 dB less than the main lobe depending on the size and design of the antenna.

Antenna beam pointing is typically accomplished with delay lines to create specific phase delays for each element, or the rows and columns of radiating elements. The switching is accomplished either with mechanical relays or solid-state switches. The resulting pointing angles are fixed and limited in number.

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Most wind profiler antenna systems are phased arrays. The actual individual radiating elements are usually either patch, Yagi-Uda or coaxial-collinear (CO-CO). They are typically installed over a metal ground plane, and have individual gain values of 6-8 dBi. In all cases the element-to- element spacing is designed specifically to create an antenna pattern amplitude null at the horizon. This is purposely done to reduce ground clutter backscatter as well as RFI.

Figure 14. Examples of wind profiler antenna elements (from left to right: Yagi-Uda, CO-CO, patch)

Array amplitude tapering often is used to reduce sidelobe levels. RWPs are susceptible to interference from nearby ground clutter and RF emissions so minimizing low angle sidelobes benefits profiler data quality, as well as reducing transmit power directed toward low elevation angles. A strong amplitude taper was used for the SDG&E XBS-T.

As with the SDG&E XBS-T (see Figure 2), various profiler manufacturers (see Figure 15) utilize a “clutter fence,” which is usually a mesh or solid metal fence angled out from the antenna to further minimize low elevation angle sidelobes. The clutter fence helps to further reduce backscatter from ground clutter, as well as reduce RFI in both directions. For cases where a unique issue exists with either clutter or RFI, an additional tall metal-mesh fence can also be built to block line-of-site radiation issues between the offending transmitter and receiver.

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Figure 15. Examples of RWP clutter fences.

One aspect of antenna sidelobe patterns is that they have directions of minimum energy between the lobes due to the layout of antenna elements. This means that by physically rotating the RWP antenna, a horizontal pattern minimum may be directed at a compass azimuth interference point (transmitter or receiver) to further optimize for spectrum management if that should become necessary. It has not yet been necessary in our experience.

4.2 Average Power and ERP Compared to other continuous transmitting radio communications systems, a radar wind profiler is a pulse system with a transmitting duty-cycle in the 1-10% range (typical). The effective pulse lengths are also very short, on the order of 1 µs and rarely extend above 8 µs, even including bi-phase modulation pulse coding (1, 4, or 8 chips typically). The inter-pulse periods (IPPs) are much longer, on the order of 50 to 100 µs.

Effective Radiated Power (ERP) describes the equivalent transmitter power as if the radiating antenna were an ideal lossless dipole radiator. EIRP similarly refers to the radiated power from an isotropic antenna. The pulse ERP for a radar wind profiler is typically high since the main beam gain of radar wind profilers (depending on the model) varies between 20 and 35 dBi. A radar wind profiler’s main beam ERP is important for the detection of backscatter, but it is much less important for understanding the possible level of interference of nearby systems since the main beam is directed vertically and rarely intercepts other receive systems. Rather, sidelobe ERP is most germane to understanding the potential impact of a radar wind profiler to another receiver system and to understanding the susceptibility of the radar itself to ground clutter and to radio frequency interference. As noted above, wind profiling radars, including the one proposed here, are designed to have low sidelobes in the horizontal direction, so sidelobe ERP is actually very low.

A result of wind profiler radar transmission is that most modern communication receiver systems, particularly those using frequency modulation (FM) or digital pulse code modulation (PCM), and especially those using spread spectrum technologies, are minimally affected by pulsed RWP signals since: a) the actual average power (5-10% of the peak) is low, b) only ~90 degree sidelobes are a factor for ERP calculation and c) the very short radar pulses are not coherent with the other system’s modulation scheme. It is, of course, key that the systems are

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not in extremely close proximity, since receiver overload or blocking might occur in the “near field”.

4.3 Pulse Shaping To minimize utilized spectrum bandwidth, most modern wind profilers use tapered pulse shaping, rather than simple square waves. In the past, pulse shaping was usually accomplished by analog filter techniques, but many modern systems use fully digital intermediate frequency (IF) transceivers with post-filtering, so now pulse shaping is accurately generated by digital means.

References Carbone, R. E., Block, J., Boselly, S. E., Carmichael, G. R., Carr, F. H., Chandrasekar, V., ... & Marshall, C., Observing Weather and Climate from the Ground Up: A Nationwide Network of Networks. US National Academy of Sciences, 2009.

ECC, “Compatibility of wind profiler radars in the Radiolocation Service (RLS) with the Radionavigation Satellite Service (RNSS) in the band 1270-1295 MHz,” European Communication Committee (ECC) Report 090, 2006.

NTIA, Manual of Regulations and Procedures for Federal Radio Frequency Management, May 2014 Revision of the May 2013 Edition (NTIA Redbook), 2014.

NTIA Microcomputer Spectrum Analysis Models (MSAM), FDR Frequency Dependent Rejection.

NTIA Report 82-100, A Guide to the Use of the ITS Irregular Terrain Model in the Area Prediction Mode, authors G.A. Hufford, A.G. Longley and W.A. Kissick, U.S. Department of Commerce, April 1982.

NTIA Report 07-447, Assessment of Federal and Non-Federal Land Mobile Radio Frequency Assignment Methodologies, May 2007.

NTIA Letter from Richard Parlow, Associate Administrator, OSM to Dr. Thomas Stanley, Chief, OET dated 17 Jan 1992, includes among other technical information, Enclosure 2, EMC analysis between Type A wind profilers and remote pickup broadcast stations, 1992.

ITU RECOMMENDATION ITU-R P.372-11 Radio noise, 2013.

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ITU RECOMMENDATION ITU-R S.1425 Transmission considerations for digital carriers using higher levels of modulation on satellite circuits, 2000.

ITU RECOMMENDATION ITU-R SM.337-6 FREQUENCY AND DISTANCE SEPARATIONS, 2008.

NTIA Report 93-301, Law, D., Sanders, F., Patrick, G., Richmond, M., Measurements of Wind Profiler EMC Characteristics, 1994.

NTIA Report 91-280, Patrick, G., Richmond, M., Assessment of Bands for Wind Profiler Accommodation (216-225, 400.15-406, and 420-450 MHz Bands), 1991.

FCC Technological Advisory Council, Receivers and Spectrum Working Group, Interference Limits Policy, The use of harm claim thresholds to improve the interference tolerance of wireless systems, 2013.

FCC OET BULLETIN No. 69, Longley-Rice Methodology for Evaluating TV Coverage and Interference, February 06, 2004

FCC/OET TM87-1, Receiver Susceptibility Measurement Relating to interference between UHF Television and Land Mobile Radio Services, 1986.

FCC "Notice of Proposed Rulemaking" NPRM-8092, ET Docket 93-59, Amendment of Section 1.206 of the Commission’s Rules to Allocate Spectrum for Wind Profiler Radars, 1993.

Radio Mobile, v 11.5.8, developed by Roger Coudé VE2DBE, 2015 (based upon ITS Irregular Terrain Model).

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