ENGINEERING REPORT: ANALYSIS OF TILLAMOOK PEOPLE S UTILITY DISTRICT PROPOSED TRANSMISSION LINE EFFECTS ON THE DIRECTIONAL ANTENNA PATTERN OF KTIL

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1 HATFIELD & DAWSON BENJAMIN F. DAWSON III, PE CONSULTING ELECTRICAL ENGINEERS TELEPHONE (206) THOMAS M. ECKELS, PE FACSIMILE (206) GREENWOOD AVE. N. STEPHEN S. LOCKWOOD, PE SEATTLE, WASHINGTON DAVID J. PINION, PE ERIK C. SWANSON, PE THOMAS S. GORTON, PE MICHAEL H. MEHIGAN, PE JAMES B. HATFIELD, PE CONSULTANT MAURY L. HATFIELD, PE ( ) PAUL W. LEONARD, PE ( ) ENGINEERING REPORT: ANALYSIS OF TILLAMOOK PEOPLE S UTILITY DISTRICT PROPOSED TRANSMISSION LINE EFFECTS ON THE DIRECTIONAL ANTENNA PATTERN OF KTIL PREPARED FOR TILLAMOOK PEOPLE S UTILITY DISTRICT MARCH 2013

2 INTRODUCTION The Tillamook People s Utility District has proposed construction of a transmission line along Oregon Highway 131, Netarts Highway. This transmission line will run adjacent to the antenna of Medium Wave (AM - Amplitude Modulated) radio station KTIL. The proposed transmission line construction includes 26 power poles and interconnecting static wire that could be potential sources of re-radiation for KTIL. This report will examine the effect of this transmission line construction on the operation of KTIL. DESCRIPTION OF NEARBY AM BROADCAST STATION Alexandra Communication, Inc. operates AM Broadcast Station KTIL. The signals broadcast from the daytime non-directional and the nighttime directional antenna systems of KTIL serve an audience estimated to be approximately 21,000 persons and reach an approximate area of 420 square miles, covering much of the northwest Oregon coast. This station operates with the following facilities: Call Sign Frequency Power Type of Facility KTIL Daytime 1590 khz 5 kw One Tower Non-Directional Antenna KTIL Nighttime 1590 khz 1 kw Two Tower Directional Antenna The transmitter site is located on a 7 acre parcel north of Oregon 131 Netarts Highway and west of Fenk Road W, in Tillamook, OR. The antenna system consists of two towers, each 150 feet tall, which make up the directional antenna array. The directional antenna operation is achieved by driving each of the towers with signals in the proper phase and amplitude arrangement to produce the desired directional radiation patterns required by the station s FCC License. Structures that are constructed nearby AM radio antenna systems are often energized by the AM signal and can become an inadvertent parasitic part of the antenna system. This can cause serious distortion to the directional antenna pattern. MODELING BACKGROUND AND CRITERIA AS IMPLEMENTED Expert MININEC is an advanced engineering tool for the design and analysis of wire antennas. Special options for analysis of commercial broadcast antennas have been added. Because of the similarity in names, it has often been stated that MININEC is but a personal computer (PC) Hatfield & Dawson Consulting Engineers

3 version of its big brother, NEC [Burke and Poggio, 1981]. Some of this confusion is described in Murray and Austin [Murry and Austin, 1994]. There are significant differences between these two codes. Both codes use the Method of Moments to solve for currents on electrically thin wires. However, each code starts with a different version of the integral formulation for the currents and fields for wires. This program was authored by J.W. Rockway and J.C. Logan. (EM Scientific). Expert MININEC was used to model the antenna arrays, and to synthesize the antenna patterns. The far-field patterns generated by MININEC replicate the FCC licensed directional antenna patterns. Hatfield & Dawson Consulting Engineers

4 Hatfield & Dawson Consulting Engineers

5 MININEC Wire Model of KTIL With Power Poles and Static Wire Hatfield & Dawson Consulting Engineers

6 Transmission Line Route Hatfield & Dawson Consulting Engineers

7 Location of KTIL Hatfield & Dawson Consulting Engineers

8 MODELING BACKGROUND We have developed a model of the KTIL(AM) nighttime antenna system that replicates the FCC licensed directional antenna pattern. The models of the night directional patterns have been verified to accurately replicate the FCC licensed antenna patterns. The proposed transmission line structures have been added to the model to determine their impact on the directional antenna pattern. The daytime non-directional system has been ignored as any distortion effects and mitigation solutions will be more pronounced in the nighttime directional array. MODELING CRITERIA MoM modeling programs commonly in use in the Medium Frequency (MF) band utilize numerical approximations to model the effects of cylindrical wires and surface patches in the presence of external electromagnetic fields or applied voltage sources. In order for the approximations used in these programs to produce accurate results, certain criteria on the geometry and electrical characteristics of the elements used in the model must be maintained. Some of these criteria are derived directly from the numerical methods used to model real world effects, and others have been determined through empirical testing and have been widely accepted as best practices in the modeling community. A summary of the criteria that should be employed when modeling the antenna arrays and the proposed structures is outlined below. 1. The system models of the antennas, and scattering structures must not violate any of the constraints of the computer program being used. 2. All modeled structures, the ground plane, and all connections between the modeled structures and the ground plane will be assumed to be lossless; with the exception that antenna base resistance may be employed when modeling the antenna systems to achieve a modeled pattern efficiency that is equivalent to the FCC specified pattern efficiency. 3. Structures that are not cylinders but that otherwise have uniform cross section, may be modeled as a cylinder with a radius equivalent to the radius of a circle having the same circumference as the physical structure being modeled. Hatfield & Dawson Consulting Engineers

9 4. For vertical structures whose cross section significantly tapers with height, the structure may be modeled using multiple wires having stepped radii that simulate the taper of the physical structure being modeled. 5. No wire segment in the model may exceed 10 electrical degrees in length at the operating frequency of 1590 khz (5.2 meters). 6. For complex structures such as the power poles and static wire, it may be necessary to create a detailed model consisting of the primary vertical legs of the structure, horizontal support bars and some interconnecting structural members. 7. The model of each structure should include the vertical support structure and any conducting elements such as grounded lightning protection cables or rods. FCC PROOF-OF-PERFORMANCE AM antenna systems operate at medium wave radio frequencies which have wavelengths of several hundred feet. The wavelength for KTIL, 1590 khz is meters (618.6 feet). The interaction of conducting poles and static wires can have a dramatic effect on the directional antenna pattern of the radio station. The FCC requires that field strength measurements be taken when it is necessary to verify that an AM directional antenna pattern is within specified limits. If the performance of an AM directional antenna needs to be verified after the station is licensed, a series of field strength measurements are taken along a straight line in each direction specified in the license as a monitor point radial, usually in a direction where the signal is minimized to prevent interference. These measurements are called a partial proof- of-performance and are only made when changes to the antenna system or the environment near the antenna system have occurred such that the antenna may be affected. Such changes can include construction of power lines and substations. A single monitor point is also specified by the station license for each monitor point radial and is measured as a part of routine operation to verify that the directional antenna pattern complies with the terms of the license. The license specifies a maximum measured field limit for each monitor point. Hatfield & Dawson Consulting Engineers

10 In MM Docket No adopted in 2009 the FCC adopted a change in proof of performance rules that no longer rely on field strength measurements but instead use internal impedance measurements with in the antenna system. These types of proofs are referred to as Moment Method Proofs and are the preferred method. One of the major benefits of the Moment Method proofs over the previous field strength proof is that proof of FCC compliance is no longer dependant on development nearby the antenna site. CONCLUSION AND RECOMMENDATIONS When the worst case (1.5 Ohm loss) effects of the transmission line poles and static wire are included in a model of the antenna and its vicinity, the pattern distortion in KTIL nighttime pattern is severe and many antenna azimuth deviate from the FCC specified antenna pattern (standard pattern). There is no practical way to detune this many structures and no single structure is the direct cause. This disturbance is largely due to the loops created by the static wire and the ground wire on the power poles. There are two ways to mitigate the disturbance to the antenna system. These are: Isolate the static wires from the ground wires using Cooper Surge Arresters (S see enclosed cut sheet.) Building the transmission line within 1.5 km of the KTIL antenna system without the static wire. However, addition of these structures would make a traditional field strength measurement proof of performance somewhat difficult. We recommend that a Moment Method Proof be completed on KTIL. Any other solutions would require relocating the transmission line or KTIL. Hatfield & Dawson Consulting Engineers

12 KTIL TILLAMOOK, OR BL khz Nighttime Electric Field Strength at 1 km radius millivolts per meter - mv/m True North Power: 1.0 kw Graph Maximum: 500 mv/m 40 Theoretical Standard Augmented Facility ID: Application ID: CDBS Antenna System ID: Towers 12 Augmentations Theoretical pattern RMS: Azimuth E E E theo std aug The theoretical pattern is used to create the standard pattern. Augmentations (if any) expand the standard pattern in specified directions. See Sections and of the FCC s Rules. AM coverage may not mirror the pattern shown here. Additional factors such as ground conductivity or skywave propagation affect how far the AM signal will travel. Patterns for stations outside the USA are based on notified parameters. AM directional patterns created before 1982 used units of 1 mv/m at 1 mile, not one kilometer. The pattern values on such plots at 1 mile will be of the values listed here. Measured pattern values may vary from values shown here. Plot is best printed on 11" by 17" or larger paper. 15 Feb 2012 Prepared by Audio Division, Media Bureau Federal Communications Commission Azimuth E E E theo std aug

13 07-Mar-13 KTIL - Tillmook PUD KTIL Nighttime Azimuth Standard Pattern Model Pattern Model WIth Power Poles & Skywire Grounded at Each Pole Model WIth Power Poles & Skywire Isolated Using Surge Arrestor at Each Pole Standard Pattern/Isolated Poles Degrees True mv/m at 1 km mv/m at 1 km mv/m at 1 km mv/m at 1 km db Hatfield & Dawson Consulting Engineers

14 07-Mar-13 KTIL - Tillmook PUD KTIL Nighttime Azimuth Standard Pattern Model Pattern Model WIth Power Poles & Skywire Grounded at Each Pole Model WIth Power Poles & Skywire Isolated Using Surge Arrestor at Each Pole Standard Pattern/Isolated Poles Degrees True mv/m at 1 km mv/m at 1 km mv/m at 1 km mv/m at 1 km db Hatfield & Dawson Consulting Engineers

15 Hatfield & Dawson Consulting Engineers 07-Mar-13 KTIL - Tillamook PUD

16 Hatfield & Dawson Consulting Engineers 07-Mar-13 KTIL - Tillamook PUD

17 Hatfield & Dawson Consulting Engineers 07-Mar-13 KTIL - Tillamook PUD

18 Hatfield & Dawson Consulting Engineers 07-Mar-13 KTIL - Tillamook PUD

25 Proposed Transmission Line Poles See attached structure drawings for conductor attachment heights above ground for typical poles. River crossing poles and poles adjacent to river crossings will be taller to grade back to typical heights. Pole # Lat Long Structure Type Structure Material '31.40"N '15.78"W Tangent Steel '31.71"N '24.31"W Angle Steel '26.96"N '30.79"W Tangent Steel '22.58"N '36.67"W Double Deadend Steel '22.51"N '38.98"W Tangent Steel '22.40"N '41.83"W Tangent Steel '22.30"N '44.27"W Tangent Steel '22.18"N '48.04"W Tangent Steel '22.07"N '52.34"W Tangent Steel '21.96"N '55.47"W Tangent Steel '21.99"N '59.18"W Tangent Steel '22.02"N '2.63"W Tangent Steel '22.05"N '6.16"W Tangent Steel '22.03"N '9.53"W Tangent Steel '22.07"N '13.35"W Tangent Steel '22.07"N '16.83"W Tangent Steel '22.15"N '20.42"W Tangent Steel '22.20"N '24.28"W Tangent Steel '22.28"N '33.07"W Double Deadend Steel '18.85"N '37.13"W Double Deadend Steel '19.59"N '44.70"W Tangent Steel '19.86"N '47.47"W Double Deadend Steel '15.09"N '49.79"W Angle Steel '11.72"N '56.12"W Tangent Steel '8.40"N '2.42"W Double Deadend Steel '11.32"N '9.89"W Angle Steel

26 Existing Radio Antennas Radio # '24.43"N '21.26"W Radio # '24.72"N '24.59"W Existing Wood Distribution Poles There are currently distribution poles located adjacent to the proposed transmission pole locations. These poles are generally framed with the phase conductors between 34' and 39' above the ground with neutral conductors framed between 27' and 31' There are two noteable exceptions that involve two river crossings. The first river crossing is located adjcent to pole no. 31 & 32, the phase conductors are framed at 43' and the neutral at 31'. The second river crossing is adjcent to pole no. 33 & 34, the phase conductors are framed at 74' and the neutral at 62'. The LIDAR ground elevation at pole 31 is 5' above the radio antenna ground elevation, pole 32 is 7', pole 33 is 10' & pole 34 is 11' above the radio antenna ground elevation.

27 01 KTIL-N Sum C:\AM\KTIL-PUD\MNEC\KTIL-N :16:27,Seg,X1,Y1,Z1,X2,Y2,Z2,r, Comment End GEOMETRY Dimensions in meters Environment: perfect ground wire caps X Y Z radius segs 1 none none Number of wires = 2 current nodes = 42 minimum maximum Individual wires wire value wire value segment length segment/radius ratio radius ELECTRICAL DESCRIPTION Frequencies (KHz) frequency no. of segment length (wavelengths) no. lowest step steps minimum maximum 1 1, Sources source node sector magnitude phase type voltage voltage Lumped loads resistance reactance inductance capacitance passive load node (ohms) (ohms) (mh) (uf) circuit C:\AM\KTIL-PUD\MNEC\KTIL-N :16:27 IMPEDANCE normalization = 50. freq resist react imped phase VSWR S11 S12 (KHz) (ohms) (ohms) (ohms) (deg) db db source = 1; node 1, sector 1 1, source = 2; node 22, sector 1 1, C:\AM\KTIL-PUD\MNEC\KTIL-N :16:27 CURRENT rms Frequency = 1590 KHz Input power = 1,000. watts Efficiency = % coordinates in meters current mag phase real imaginary no. X Y Z (amps) (deg) (amps) (amps) Page 1

28 01 KTIL-N Sum GND E END GND END Page 2

29 02 KTIL-N CMT C:\AM\KTIL-PUD\MNEC\KTIL-N :16:53 CURRENT MOMENTS(amp-meters) rms Frequency = 1590 KHz Input power = 1,000. watts vertical current moment wire magnitude phase (deg) magnitude phase (deg) Page 1

30 03 KTIL-N Pat C:\AM\KTIL-PUD\MNEC\KTIL-N :15:43 RADIATION PATTERN rms geographic coordinate system Radial distance (meters) = 1,000. Frequency = 1,590. KHz Input power = 1,000. watts Efficiency = % elevation azimuth E-theta E-phi angle angle mag (mv/m) phase (deg) mag (mv/m)phase Page 1

31 03 KTIL-N Pat Page 2

32 04 KTIL-PUD-TW Sum C:\AM\KTIL-PUD\MNEC\KTIL-PUD-TW :18:24,Seg,X1,Y1,Z1,X2,Y2,Z2,r, Comment End GEOMETRY Dimensions in meters Environment: perfect ground wire caps X Y Z radius segs 1 none none none , , none , , none none none none none none none none none none none none none none none none none none none none none none none , , Page 1

33 04 KTIL-PUD-TW Sum 28 none , , none , , none , none none none none none none none none none none none none none none none none none none none none none none , none , , Number of wires = 53 current nodes = 793 minimum maximum Individual wires wire value wire value segment length segment/radius ratio radius Page 2

34 04 KTIL-PUD-TW Sum ELECTRICAL DESCRIPTION Frequencies (KHz) frequency no. of segment length (wavelengths) no. lowest step steps minimum maximum 1 1, Sources source node sector magnitude phase type voltage voltage Lumped loads resistance reactance inductance capacitance passive load node (ohms) (ohms) (mh) (uf) circuit C:\AM\KTIL-PUD\MNEC\KTIL-PUD-TW :18:24 IMPEDANCE normalization = 50. freq resist react imped phase VSWR S11 S12 (KHz) (ohms) (ohms) (ohms) (deg) db db source = 1; node 1, sector 1 1, source = 2; node 22, sector 1 1, C:\AM\KTIL-PUD\MNEC\KTIL-PUD-TW :18:24 CURRENT rms Frequency = 1590 KHz Input power = 1,000. watts Efficiency = % coordinates in meters current mag phase real imaginary no. X Y Z (amps) (deg) (amps) (amps) GND END GND Page 3

35 04 KTIL-PUD-TW Sum END GND , , , , , END , GND , E , E , E , E , E-03 END , E-03 GND END E-03 GND E E E E E END E GND END GND END GND END GND Page 4

36 04 KTIL-PUD-TW Sum END GND END GND END GND E E END GND END GND END GND END GND END GND END E-03 GND E END E GND E E E Page 5

37 04 KTIL-PUD-TW Sum END GND END GND END GND END GND END GND END GND END GND , , , , , END , GND , , , , , END , J , , , E , E , E , E , E E E , E E E , E E E , E E E , E , E , E Page 6

38 04 KTIL-PUD-TW Sum , E , , , , , , , , E , E , E , E , E , E E E , E E E , E E E , E E E , E , E , E , E , , , , , END , J , , , , , E , E , E , E , E , E E-03 8.E E E E E E E E E E E E E E E E E Page 7

39 04 KTIL-PUD-TW Sum END J E E E E E E E E E E E E E E E E E END J E E E E E E E-03 END J E E Page 8

40 04 KTIL-PUD-TW Sum E E END J E E E E END E J E E E E E E E END J E E E E E E E END J Page 9

Prediction of AM Broadcast Field Strengths Radio Station KDKO, 1510 khz, Littleton, CO Day Pattern US West Tower DEN-118. September 15, 1997

Prediction of AM Broadcast Field Strengths Radio Station KDKO, 1510 khz, Littleton, CO Day Pattern US West Tower DEN-118 September 15, 1997 Prepared by: Jay M. Jacobsmeyer, P.E. Pericle Communications