RFHaz

Our new RF Environmental Prediction Program – RFHAZ-3™

RFHAZ_3_main_newIntroduction

The FCC has published the OET #65 bulletin and its revision. The latest document specifies how FM, TV stations and communication antennas must protect the public and workers from excessive exposure to RF radiation. The FCC’s more stringent rules require broadcasters to protect uncontrolled areas at 20 percent of the former maximum. Controlled areas, where access is limited, continue to be protected at the former levels. RFHAZ 3 allows for graphical examination of multiple antennas at numerous RF density scales from a minute observation with maximums not exceeding 50 microwatts/sq centimeter to a maximum scale level of 3000 microwatts/sq centimeter. By using the “Graph Type” radio buttons, the user can choose to display the graph as either “Power Density” or as a “Percent Maximum” of the FCC levels for controlled or uncontrolled areas.

For FM calculations, the user can select to use the EPA studied antennas for which the vertical patterns are included or manufacturer’s patterns can be loaded from disk file or user created from printed tables. When the program uses the EPA patterns, it combines formulas from the revised OET #65 bulletin with EPA researched element and array patterns as published in PB85-2458-68, “Engineering Assessment of the Potential Impact of Federal Radiation Protection Guidance on the AM, FM and TV Broadcast Services.” The user can select R.F. emissions calculations to consider the effect of a mix of array elements and element spacings (in wavelengths). In addition to a graph, RFHAZ 3 will print a tabulation of both the vertical and horizontal radiation density levels and, when multiple antennas are used their sums in microwatts per square centimeters from the tower base to 100 or increments to 1000 meters from the base. The program considers the impact of antenna arrays having from 1 to 16 bays as well as those with less than full wave spacings.

For TV and DTV calculations RFHAZ 3 gives the user the option to apply the manufacturer’s vertical elevation field elevation values on the path of interest from the antenna to the ground. You can produce graphs of the radiation density from the base of a tower to points up to 1000 meters from the base. The program will compute power densities and percentages of the maximum FCC standard for the frequencies in use. Two or more antennas of different types, heights and ERP, such as FM, LPTV and DTV, can be graphed along with the composite summation of all three. Tables of RF density values which include the graph’s image can printed for individual antennas or for the composite of all antennas in the study.

EPA Studies

Select “FM” as the type of study and “OET EPA” as the OET method, Enter the horizontal and the vertical ERPs by using the slider or by typing in the values on the text box located after each slider. Select the number of bays to be used on the antenna and the spacing between bays. Then, enter the antenna’s center of radiation above ground in meters and subtract two meters to predict the power levels or percentages at head height. Finally, select the antenna model to be used. Each antenna will have a EPA type number which the FCC will need when it examines your submission. The types run from 1 through 9 and also appear on the graph heading when the EPA model is used.

There is no “Enter” or calculate buttons on this form. When you change a value the antenna’s power density graph is recalculated. The screen above shows that the power density at the antenna base is 314.7 microwatts per square centimeter. The value usually defaults to the location of the base of the antenna, but other values may be found along a horizontal distance from the base by clicking the graph at the desired distance or by moving the “Distance in Meters to Tower Base” slider. If the “Controlled” radio button were set to “No”, the maximum environmental power density would be changed to 200 microwatts per square centimeter. For TV analysis, these controlled and uncontrolled maximum values will increase for frequencies above the VHF range (channels 2-13). The percentage of the OET 65 maximum is shown below the power density text box. The graph shown above is displayed in the “Percent Maximum” mode. Since the EPA studied only FM antennas, the OET EPA method is available only for FM calculations.

Standard OET

These calculations are made by clicking the OET #65 button. In this situation, only the values at the base of the tower are calculated. “Note: as in all studies, you must subtract 2 meters from the COR above ground for calculating the power density at head height.” If the study is for FM, the program will automatically move the “Field” slider to 1, which means that the vertical elevation field will be 100% of the calculated OET value. This is often called a “worst case” calculation. If a TV study has been selected, the field will automatically move to 0.2. This assumes that the antenna in use is a typical high gain antenna where the field toward the nadir is usually significantly attenuated. The user can adjust the field values slider as is seen fit. The standard OET mode does not provide a graph and the printouts in this mode use the same vertical elevation field value for all distances from the tower.

OET Manu

This mode is available for FM, TV and DTV. When doing calculations it is sometimes necessary to use the manufacturer’s provided vertical elevation field values. Once the radio button “OET Manu” is selected the vertical elevation field window will open.

RFHaz_3_tvThis mode is available for FM, TV and DTV. When doing calculations it is sometimes necessary to use the manufacturer’s provided vertical elevation field values. Once the radio button “OET Manu” is selected the vertical elevation field window will open.

RFHAZ_3_vepVertical elevation fields from numerous bayed antennas were supplied by ERI and have been included with the program. Vertical field patterns from the ERI, Inc. EBSP antenna program can be loaded directly by using the dropdown box for loading “ERI” vertical elevation patterns.

Click the “Load” button to load an existing pattern from the provided pattern database or type in a different pattern and save if for future use. (RFHaz 3 comes with the standard vertical elevation field patterns provided by ERI, Inc. These patterns will be identical for most similarly designed antenna patterns throughout the industry.) To type in a pattern point by point, clear all existing entries by using the “Clear” button, then select the “Add Point” button and provide the elevation azimuth of the point and the field value. Do this until you have set up the entire pattern. You can enter a pattern name, electrical and mechanical beam tilt and the tilt azimuth. You can remove or edit a point by first highlighting the point and then by clicking the “Remove” or “Edit” buttons respectively. Finally, click the “Save” button and then the “Exit” button to complete the process and return to the Main RFHAZ 3 screen. In the vertical field graph example shown above, the ERP SHPX10F was loaded. This antenna is a 10-bay full-wave FM antenna. When the antenna model reads SHPX10H it is a half-wave model.

Mulitple Stations:

The program will produce a composite graph of up to a dozen antennas of various types. To add antennas to a study, first use the OET EPA (for FM) or the “OET Manu” for FM, TV or DTV studies to produce a graph, then click “Multiple Stations” then select “Add Station” or click the shortcut “add” radio button, found in the “Multiple Stations…” box. To add an antenna previously saved using “Disk Write”, click “Multiple Stations”, then click “Load Station”. The saved stations will appear on your graph and the composite will be displayed.

RFHAZ_3_MultiThe two antennas added in this study are shown in black, while their composite summation is shown in red. If you are in the middle of a multiple antenna study and you wish to switch to the OET #65, standard method, click the “OET #65” radio button, perform any calculations you wish and then click the “Multiple Stations” menu and then click “Return to Multiple Graph” to return to your multiple station study. You can click your mouse anywhere on the graph and the program will report the composite power density and percent of the maximum at that location from the antenna base.

Disk Write

This menu will write the resident antenna to a power density file, having the extension “.DEN”. These are comma delimited files that can be loaded into another program such as Excel, or they can be loaded into the program to be displayed as explained above.

Other RF

RFHAZ_3_otherUse this module to calculate the non-ionizing RF emissions of antennas on the non-broadcast frequencies.

HELP

Clicking F1, or “Help” will bring up the help screen.

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