Broadcast Wind is an engineering consulting company founded in 2010 by broadcast industry veterans to provide RF interference analysis for the wind and broadcasting industries and to help establish the standards needed to ensure non-interference of turbine blades with RF signals. Clients include US broadcast station groups, the United States Department of Agriculture, Exelon, NextEra Energy Resources LLC, and Invenergy LLC. Projects included AM, FM and television interference studies, and baseline RF field studies (taken prior to wind farm build-out). Broadcast Wind personnel have presented to wind energy and broadcast industry trade groups, teaching the importance of identifying radio and television interference issues prior to wind farm construction. Broadcast Wind specializes in Electromagnetic Interference Analysis (EIA) required by governing bodies from wind farm developers during the wind farm permitting process with special experience in interfacing with broadcasters to provide accurate information about a wind farm’s effects on their signals and to relieve concerns about signal loss.
TV Station Signals
Broadcast Wind provides wind farm developers and other interested stakeholders (permitting agencies, investors, etc.) with predictions of the effects of proposed wind farms on television signals. Included in these predictions are estimates of number of viewers that would be affected – both directly off-air and via cable from providers that pick up local programming off air. Estimates of impairment to cable off-air pick-up is an important, although frequently forgotten, component of an EIA because of the large number of viewers that may be affected. There are no national databases of cable companies’ off-air receive sites. Local research must be conducted to identify cable off-air signal pick-up points that may be affected by construction of a wind farm..
A computer simulation desktop study is used to assess potential for signal impairment due to a proposed wind farm. The strength of signals from television stations whose coverage areas include the proposed wind farm site are simulated in the regions surrounding the proposed site for with and without the wind farm. The software models electromagnetic wave propagation taking into account effects of terrain variation on the signal. The individual wind turbines are modeled as additional path obstructions in the terrain.
Our OET-69 analysis software divides the area within a station’s protected contour into a matrix of square grid cells (0.5 km on a side) and then uses the Longley-Rice propagation model to predict the field strength at each individual cell. The output of the studies are analyzed to determine which cells (if any) show a critical reduction in the predicted field strength.
The cells in the Area of Potential Interference are where the simulated signal strength dropped to an unacceptable level, post construction.
Probe Data – TV Dashboard
Broadcast Wind uses proprietary stationary remote RF probes to provide our wind farm developers and stakeholders with long term TV signal strength and signal quality data critical locations prior to and following the construction of wind farms. Similarly to the way meteorological gear is used by the wind industry, prior to and following wind farm construction to gather wind data over a period of time, our RF probes capture TV signal metrics through changes in seasons, and atmospheric conditions before, during, and after wind farm construction. The probe data provides Broadcast Wind and the wind farm developers with reliable documentation of changes (if any) to signal quality consequential to construction.
The probe data is forwarded to Broadcast Wind’s offices and optionally to a client’s office where it can be displayed on a concise graphical data dashboard and can be programmed to provide alerts if parameters go out of defined limits. Dashboard data can be viewed remotely by hour, day, month and year. A roll of the mouse allows the user to see what was going on with atmospheric conditions at the time of the probe reading.
In the following dashboard example we see correlation between UHF signal variation and precipitation. Precipitation, high wind, time of day, and seasonal changes can all play a role in UHF DTV signal propagation.
TV Probe Metrics:
The top three graphical metric lines are displayed on a common percent scale for convenience of visualization. The fourth, margin, is displayed in dBmv. The inset box provides the measurement data.
- The TV signal “SEQ” tells us whether the video signal is watchable. An SEQ of 99% would mean that the viewer sees a ”hit” (I.e. pixilation) to the video 1% of the time that they are watching.
- Signal strength in dBmv and signal quality (MER) in dB are also captured.
- “Margin” describes how much signal strength buffer there is within the channel before the signal would start to fall apart. More margin means a stronger, more stable video signal.
No single metric completely describes the quality of the signal reception. The value of the dashboard is that it presents multiple metrics that can be correlated with each other and with external factors.
AM and FM Broadcast Radio Stations
AM broadcast stations’ exclusion distance varies depending upon antenna type and broadcast frequency. Omni directional (non-directional) antennas, have an exclusion distance equal to 1 wavelength. For AM antenna arrays (directional antennas), the exclusion distance is the lesser of 10 wavelengths or 3 kilometers. AM broadcast coverage problems are only anticipated when AM broadcast antennas are located within the exclusion distance limit of wind turbine towers.
The coverage of FM stations at distances greater than 4.0 km from wind turbines, is not subject to degradation. FM transmitters with antennas closer than 4.0 km from proposed wind turbines can, under some conditions, experience a compromised signal.
Similar to the TV signal analysis above, Broadcast Wind conducts a desktop study to determine potential areas of interference for FM radio stations. Remote RF signal probes accessorized with long term FM signal quality logging capabilities are placed within areas with the highest risk for signal compromise prior to, during and following the proposed wind farm construction.
Probe Data – FM Dashboard
Broadcast Wind’s remote stationary probes can also monitor FM radio signals and forward them to our offices and to a client’s offices for display on a dashboard. FM signal metrics are stored on the cloud where they are available for review by Broadcast Wind’s clients.
Point-to-Point Microwave Systems
Point-to-point microwaves that may be affected by the installation of wind farms operate over a wide range of frequencies (900 MHz – 23 GHz). These microwave systems provide a wide range of telecommunication backhaul throughout the country supporting essential services such as land based telephone services, cellular networks, personal communication services; data and internet interconnects, network controls for utilities and railroads, and various video services.
Every point-to-point interconnect analysis must begin with solid geolocation information. In some cases, a field survey may be recommended to validate tower coordinates found on governmental web sites to assure predictive model accuracy and to avoid issues of interference following construction.
Once the accuracy of GPS data is assured, a two dimensional (2D) analysis is performed to determine whether any microwave signals intersect a proposed wind turbine’s footprint.
An example of a 2D analysis showing the microwave beam apparently intersecting a turbine blade.
Once a 2D analysis is complete, a 3D analysis (pictured below) allows us to determine whether the signal is able to safely pass under or above the turbine blades without interference from the blades.
Point-to-Multipoint Microwave Systems
Wireless Internet Service Providers (WISPs) deliver Internet and other data services via radio transmission to business and/or residential subscribers. WISPs can use frequency bands in both licensed and unlicensed spectrums. Many rural community WISPs operate in the unlicensed spectrum since the initial capital outlay and ongoing operating costs are low. The most common unlicensed bands used for this purpose are the 900 MHz, 2.4 GHz, and 5.8 GHz bands. Since there aren’t any governmental databases containing local WISP information, site surveys and local town business research is needed to identify, and work with major WISP operators prior to construction and to help plan for and mitigate WISP user interference issues following construction. Broadcast wind can identify the WISP service providers and receivers in the vicinity of a proposed wind farm for clients and determine by 2D and 3D analysis if the blades of any of the proposed turbines will interfere with the WISP subscribers’ signals.
Land Mobile and Emergency Services
Evaluation is needed for first responder entities: police, fire, emergency medical services, emergency management, hospitals, public works, transportation and other state, county, and municipal agencies. Generally land mobile and emergency radio systems are designed with multiple transmitters to provide redundancy so the service will not be interrupted as the receiving radio moves into and out of areas of signal blockage. Never-the-less a thorough assessment of the effect of a proposed wind farm on emergency services radio signals is an important, yet frequently overlooked aspect of an electromagnetic impact analysis. The building of a densely populated wind farm can be analogous to the placement of a city with hundreds of tall structures between an emergency transmitter and the emergency responder. If signal levels are attenuated following construction, higher powered transmitters, repeaters or signal boosters may be employed to fill the compromised area. The key to success in this area is the performance of a thorough RF field analysis prior to construction. An analysis of this type will identify the industrial and business land mobile radio systems and commercial E911 operators near the proposed wind energy facility.
Mobile Phone Systems
Modern mobile phones support a wide variety of personal communication services including telephony, text messaging, email, and internet access. The major US mobile phone service providers currently support three digital technologies: legacy 2G (voice and limited data), main stream 3G and newer, faster 4G. Mobile phone services are divided into three categories, each operating in its own frequency bands. Advanced Wireless Service (AWS), Personal Communication Service (PCS), and Cellular (CLR). They hold licenses on an area-wide basis which are typically comprised of several counties.
Wind turbines present no significant threat to mobile phone services. The mobile phone system architecture is based on low-latency packet switching and redundant cellular geographic coverage. Packets are dynamically routed among cells as mobile phones change location and as network traffic changes. A given mobile phone conversation is typically made up of packets that travel different routes and are assembled seamlessly at their destination. If a given cellular link is unavailable for any reason – interference from a wind turbine or other - the packet is automatically switched to another cell with no interruption of service. The user of the phone is unaware of cellular transitions, so will not be affected by any that may be triggered by a wind turbine.
Government Radar Systems
Wind Farm siting can potentially affect government radar systems. The Department of defense offers a Preliminary Screening Tool that can be used by wind farm developers to determine if there will be interference to air defense and homeland security radars (long range radars), to weather surveillance radar – Doppler radar (NEXRAD), or to military operations radars. Broadcast Wind can assist clients with preparation and use of this preliminary screening tool.
The FAA requires that all developers proposing a wind farm with turbines that exceed 200 feet above ground level file a Notice of Proposed Construction or Alteration form. For each turbine in the farm the form must specify the turbine ID number, latitude and longitude in degrees, minutes and seconds (NAD 83), site elevation, height above ground level (AGL), overall height above mean sea level (AMSL), and preferred marking and lighting. Upon approval of the proposal, the FAA will issue a Determination of No Hazard. Broadcast Wind can assist clients with preparation and submission of the Notice of Proposed Construction or Alteration form to the FAA.
Commercial Doppler Radar
Commercial Doppler radars are located on television towers to take advantage of their height. They are either operated by the broadcaster to support the station’s local weather forecasting service or leased to other commercial parties for private weather monitoring or forecasting. A wind developer needs to know if his turbines will be in the line of sight of any Doppler radars. The curvature of the earth determines the minimum separation distance below which a wind turbine is in the line of sight of a distant radar. If the separation distance is less than the sum of the distances to the horizon of each object the turbine will be in the radar’s line of sight.
The separation distance below which a turbine is in the line of sight is given by the following equation.
Dseparation = 3.57 x ((Hturbine)1/2 + (Hradar)1/2) x 1000
Where all dimensions are in the same units.
For example, a turbine with blade tip height 150 meters above ground will be within the line of sight of a radar on a tower 300 meters above ground if the distance between them is less than 106 kilometers.
Broadcast Wind can locate and identify the commercial Doppler radars within line of sight of the turbines in a proposed wind farm for clients.
The survey can be extended to on-site verification of tower locations in case there are errors in the location information on file in registered data bases. This verification will ensure the accuracy of the predicted impact of the wind turbines on microwave, television, and radio signals. Broadcast Wind can identify and confirm the precise location of all communications towers in the vicinity of a proposed wind farm for clients.
Accurate pre-construction identification and characterization of potential interference to electromagnetic transmissions is vital to the success of a wind energy project, both for permitting and for avoidance of post-construction problems. Television and radio broadcasting signals are especially critical because they directly impact the public. At the permitting stage an energy developer can encounter local resistance based on fear of loss of television or radio reception and after construction it can be confronted with costly claims for remediation of (real or imagined) service loss.
Broadcast Wind can provide the full spectrum of electromagnetic interference assessment. In addition we bring special expertise and experience in areas of television and radio broadcasting. This experience includes detailed characterization of the predicted effect of proposed wind farms on broadcasting signals with the added benefit of remote probes for long term in-the-field monitoring of signal strength prior to and after construction. Long term monitoring provides the developer with forensic evidence that can protect him from invalid claims for restoration of service. Our experience also includes interfacing with broadcasters at the beginning of a project to relieve possible exaggerated or misplaced fears that could lead to avoidable obstacles to successful permitting.
 FCC OET BULLETIN No. 69, Longley-Rice Methodology for Evaluating TV Coverage and Interference, February 6, 2004
 FAA Form 7460-1