SPLAT!(1)

NAME
splat An RF Signal Propagation, Loss, And Terrain analysis tool

SYNOPSIS
splat
[-t transmitter_site.qth]
[-r receiver_site.qth]
[-c rx antenna height for LOS coverage analysis (feet/meters) (float)]
[-L rx antenna height for ITM coverage analysis (feet/meters) (float)]
[-p terrain_profile.ext]
[-e elevation_profile.ext]
[-h height_profile.ext]
[-H normalized_height_profile.ext]
[-l ITM_profile.ext]
[-o topographic_map_filename.ppm]
[-b cartographic_boundary_filename.dat]
[-s site/city_database.dat]
[-d sdf_directory_path]
[-m earth radius multiplier (float)]
[-f frequency (MHz) for Fresnel zone calculations (float)]
[-R maximum coverage radius (miles/kilometers) (float)]
[-dB threshold beyond which contours will not be displayed]
[-gc ground clutter height (feet/meters) (float)]
[-fz Fresnel zone clearance percentage (default = 60)]
[-ano alphanumeric output file name]
[-ani alphanumeric input file name]
[-udt user_defined_terrain_file.dat]
[-log logfile.ext]
[-n]
[-N]
[-nf]
[-sc]
[-dbm]
[-ngs]
[-geo]
[-kml]
[-gpsav]
[-metric]
[-olditm]

DESCRIPTION
SPLAT! is a powerful terrestrial RF propagation and terrain analysis tool for the spectrum between 20 MHz and 20 GHz. SPLAT! is free software, and is designed for operation on Unix and Linux-based workstations. Redistribution and/or modification is permitted under the terms of the GNU General Public License, Version 2, as published by the Free Software Foundation. Adoption of SPLAT! source code in proprietary or closed-source applications is a violation of this license and is strictly forbidden.

SPLAT! is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY, without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

INTRODUCTION
Applications of SPLAT! include the visualization, design, and link budget analysis of wireless Wide Area Networks (WANs), commercial and amateur radio communication systems above 20 MHz, microwave links, frequency coordination and interference studies, and the prediction of analog and digital terrestrial radio and television contour regions.

SPLAT! provides RF site engineering data such as great circle distances and bearings between sites, antenna elevation angles (uptilt), depression angles (downtilt), antenna height above mean sea level, antenna height above average terrain, bearings, distances, and elevations to known obstructions, Irregular Terrain Model path attenuation, and received signal strength. In addition, the minimum antenna height requirements needed to clear terrain, the first Fresnel zone, and any user-definable percentage of the first Fresnel zone are also provided.

SPLAT! produces reports, graphs, and high resolution topographic maps that depict line-of-sight paths, and regional path loss and signal strength contours through which expected coverage areas of transmitters and repeater systems can be obtained. When performing line-of-sight and Irregular Terrain Model analyses in situations where multiple transmitter or repeater sites are employed, SPLAT! determines individual and mutual areas of coverage within the network specified.

INPUT FILES
SPLAT! is a command-line driven application and reads input data through a number of data files. Some files are mandatory for successful execution of the program, while others are optional. Mandatory files include digital elevation topography models in the form of SPLAT Data Files (SDF files), site location files (QTH files), and Irregular Terrain Model parameter files (LRP files). Optional files include city location files, cartographic boundary files, user-defined terrain files, path loss input files, antenna radiation pattern files, and color definition files.

SPLAT DATA FILES
SPLAT! imports topographic data in the form of SPLAT Data Files (SDFs). These files may be generated from a number of information sources. In the United States, SPLAT Data Files can be generated through U.S. Geological Survey Digital Elevation Models (DEMs) using the postdownload and usgs2sdf utilities included with SPLAT!. USGS Digital Elevation Models compatible with these utilities may be downloaded from:

    http://edcftp.cr.usgs.gov/pub/data/DEM/250/.

Significantly better resolution and accuracy can be obtained through the use of SRTM Version 2 digital elevation models, especially when supplemented by USGS-derived SDF data. These one-degree by one-degree models are the product of the Space Shuttle STS-99 Radar Topography Mission, and are available for most populated regions of the Earth. SPLAT Data Files may be generated from 3 arc-second SRTM-3 data using the included srtm2sdf utility. SRTM-3 Version 2.1 data may be obtained through anonymous FTP from:

    http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/

Note that SRTM filenames refer to the latitude and longitude of the southwest corner of the topographic dataset contained within the file. Therefore, the region of interest must lie north and east of the latitude and longitude provided in the SRTM filename.

Even greater resolution and accuracy can be obtained by using 1 arc-second SRTM-1 Version 2.1 topography data. This data is available for the United States and its territories and possessions, and may be downloaded from:

    http://dds.cr.usgs.gov/srtm/version2_1/SRTM1/

High resolution SDF files for use with SPLAT! HD may be generated from data in this format using the srtm2sdf-hd utility.

Despite the higher accuracy that SRTM data has to offer, some voids in the data sets exist. When voids are detected, the srtm2sdf and srtm2sdf-hd utilities replace them with corresponding data found in usgs2sdf generated SDF files. If USGS-derived SDF data is not available, voids are handled through adjacent pixel averaging, or direct replacement.

SPLAT Data Files contain integer value topographic elevations in meters referenced to mean sea level for 1-degree by 1-degree regions of the Earth. SDF files can be read by SPLAT! in either standard format (.sdf) as generated directly by the usgs2sdf, srtm2sdf, and srtm2sdf-hd utilities, or in bzip2 compressed format (.sdf.bz2). Since uncompressed files can be read slightly faster than files that have been compressed, SPLAT! searches for needed SDF data in uncompressed format first. If uncompressed data cannot be located, SPLAT! then searches for data in bzip2 compressed format. If no compressed SDF files can be found for the region requested, SPLAT! assumes the region is over water, and will assign an elevation of sea-level to these areas.

This feature of SPLAT! makes it possible to perform path analysis not only over land, but also between coastal areas not represented by Digital Elevation Model data. However, this behavior of SPLAT! underscores the importance of having all the SDF files required for the region being analyzed if meaningful results are to be expected.

SITE LOCATION (QTH) FILES
SPLAT! imports site location information of transmitter and receiver sites analyzed by the program from ASCII files having a .qth extension. QTH files contain the site's name, the site's latitude (positive if North of the equator, negative if South), the site's longitude (in degrees West, 0 to 360 degrees, or degrees East 0 to -360 degrees), and the site's antenna height above ground level (AGL), each separated by a single line-feed character. The antenna height is assumed to be specified in feet unless followed by the letter m or the word meters in either upper or lower case. Latitude and longitude information may be expressed in either decimal format (74.6864) or degree, minute, second (DMS) format (74 41 11.0).

For example, a site location file describing television station WNJT-DT, Trenton, NJ (wnjt-dt.qth) might read as follows:

        WNJT-DT
        40.2828
        74.6864
        990.00

Each transmitter and receiver site analyzed by SPLAT! must be represented by its own site location (QTH) file.

IRREGULAR TERRAIN MODEL PARAMETER (LRP) FILES
Irregular Terrain Model Parameter data files are required for SPLAT! to determine RF path loss, field strength, or received signal power level in either point-to-point or area prediction mode. Irregular Terrain Model parameter data is read from files having the same base name as the transmitter site QTH file, but with a .lrp extension. SPLAT! LRP files share the following format (wnjt-dt.lrp):

        15.000 ; Earth Dielectric Constant (Relative permittivity)
        0.005 ; Earth Conductivity (Siemens per meter)
        301.000 ; Atmospheric Bending Constant (N-units)
        647.000 ; Frequency in MHz (20 MHz to 20 GHz)
        5 ; Radio Climate (5 = Continental Temperate)
        0 ; Polarization (0 = Horizontal, 1 = Vertical)
        0.50 ; Fraction of situations (50% of locations)
        0.90 ; Fraction of time (90% of the time)
        46000.0 ; Effective Radiated Power (ERP) in Watts (optional)

If an LRP file corresponding to the tx_site QTH file cannot be found, SPLAT! scans the current working directory for the file "splat.lrp". If this file cannot be found, then default parameters will be assigned by SPLAT! and a corresponding "splat.lrp" file containing these default parameters will be written to the current working directory. The generated "splat.lrp" file can then be edited by the user as needed.

Typical Earth dielectric constants and conductivity values are as follows:

                        Dielectric Constant Conductivity
        Salt water : 80 5.000
        Good ground : 25 0.020
        Fresh water : 80 0.010
        Marshy land : 12 0.007
        Farmland, forest : 15 0.005
        Average ground : 15 0.005
        Mountain, sand : 13 0.002
        City : 5 0.001
        Poor ground : 4 0.001

Radio climate codes used by SPLAT! are as follows:

        1: Equatorial (Congo)
        2: Continental Subtropical (Sudan)
        3: Maritime Subtropical (West coast of Africa)
        4: Desert (Sahara)
        5: Continental Temperate
        6: Maritime Temperate, over land (UK and west coasts of US & EU)
        7: Maritime Temperate, over sea

The Continental Temperate climate is common to large land masses in the temperate zone, such as the United States. For paths shorter than 100 km, there is little difference between Continental and Maritime Temperate climates.

The seventh and eighth parameters in the .lrp file correspond to the statistical analysis provided by the ITM model. In this example, SPLAT! will return the maximum path loss occurring in 50% of situations (fraction of situations, or Location Variability) 90% of the time (fraction of time, or Time Variability). This is often denoted as F(50,90) in Longley-Rice studies. In the United States, an F(50,90) criteria is typically used for digital television (8-level VSB modulation), while F(50,50) is used for analog (VSB-AM+NTSC) broadcasts.

For further information on ITM propagation model parameters, please refer to: http://www.its.bldrdoc.gov/resources/radio-propagation-software/itm/itm.aspx and http://www.softwright.com/faq/engineering/prop_longley_rice.html

The last parameter in the .lrp file corresponds to the transmitter's Effective Radiated Power (ERP), and is optional. If it is included in the .lrp file, then SPLAT! will compute received signal strength levels and field strength level contours when performing ITM studies. If the parameter is omitted, path loss is computed instead. The ERP provided in the .lrp file can be overridden by using SPLAT!'s -erp command-line switch. If the .lrp file contains an ERP parameter and the generation of path loss rather than field strength contours is desired, the ERP can be assigned to zero using the -erp switch without having to edit the .lrp file to accomplish the same result.

CITY LOCATION FILES
The names and locations of cities, tower sites, or other points of interest may be imported and plotted on topographic maps generated by SPLAT!. SPLAT! imports the names of cities and locations from ASCII files containing the location of interest's name, latitude, and longitude. Each field is separated by a comma. Each record is separated by a single line feed character. As was the case with the .qth files, latitude and longitude information may be entered in either decimal or degree, minute, second (DMS) format.

For example (cities.dat):

        Teaneck, 40.891973, 74.014506
        Tenafly, 40.919212, 73.955892
        Teterboro, 40.859511, 74.058908
        Tinton Falls, 40.279966, 74.093924
        Toms River, 39.977777, 74.183580
        Totowa, 40.906160, 74.223310
        Trenton, 40.219922, 74.754665

A total of five separate city data files may be imported at a time, and there is no limit to the size of these files. SPLAT! reads city data on a "first come/first served" basis, and plots only those locations whose annotations do not conflict with annotations of locations read earlier in the current city data file, or in previous files. This behavior minimizes clutter in SPLAT! generated topographic maps, but also mandates that important locations be placed toward the beginning of the first city data file, and locations less important be positioned further down the list or in subsequent data files.

City data files may be generated manually using any text editor, imported from other sources, or derived from data available from the U.S. Census Bureau using the citydecoder utility included with SPLAT!. Such data is available free of charge via the Internet at: http://web.archive.org/web/20130331172800/http://www.census.gov/geo/www/cob/bdy_files.html, and must be in ASCII format.

CARTOGRAPHIC BOUNDARY DATA FILES
Cartographic boundary data may also be imported to plot the boundaries of cities, counties, or states on topographic maps generated by SPLAT!. Such data must be of the form of ARC/INFO Ungenerate (ASCII Format) Metadata Cartographic Boundary Files, and are available from the U.S. Census Bureau via the Internet at: http://web.archive.org/web/20130331144934/http://www.census.gov/geo/www/cob/co2000.html#ascii and http://web.archive.org/web/20130507075658/http://www.census.gov/geo/www/cob/pl2000.html#ascii. A total of five separate cartographic boundary files may be imported at a time. It is not necessary to import state boundaries if county boundaries have already been imported.

PROGRAM OPERATION
SPLAT! is invoked via the command-line using a series of switches and arguments. Since SPLAT! is a CPU and memory intensive application, this type of interface minimizes overhead and lends itself well to scripted (batch) operations. SPLAT!'s CPU and memory scheduling priority may be modified through the use of the Unix nice command.

The number and type of switches passed to SPLAT! determine its mode of operation and method of output data generation. Nearly all of SPLAT!'s switches may be cascaded in any order on the command line when invoking the program. Simply typing splat on the command line will return a summary of SPLAT!'s command line options:

               --==[ SPLAT! v1.4.2 Available Options... ]==--
     -t txsite(s).qth (max of 4 with -c, max of 30 with -L)
     -r rxsite.qth
     -c plot LOS coverage of TX(s) with RX antenna at X feet/meters AGL
     -L plot path loss map of TX based on an RX at X feet/meters AGL
     -s filename(s) of city/site file(s) to import (5 max)
     -b filename(s) of cartographic boundary file(s) to import (5 max)
     -p filename of terrain profile graph to plot
     -e filename of terrain elevation graph to plot
     -h filename of terrain height graph to plot
     -H filename of normalized terrain height graph to plot
     -l filename of path loss graph to plot
     -o filename of topographic map to generate (.ppm)
     -u filename of user-defined terrain file to import
     -d sdf file directory path (overrides path in ~/.splat_path file)
     -m earth radius multiplier
     -n do not plot LOS paths in .ppm maps
     -N do not produce unnecessary site or obstruction reports
     -f frequency for Fresnel zone calculation (MHz)
     -R modify default range for -c or -L (miles/kilometers)
    -sc display smooth rather than quantized contour levels
    -db threshold beyond which contours will not be displayed
    -nf do not plot Fresnel zones in height plots
    -fz Fresnel zone clearance percentage (default = 60)
    -gc ground clutter height (feet/meters)
   -ngs display greyscale topography as white in .ppm files
   -erp override ERP in .lrp file (Watts)
   -ano name of alphanumeric output file
   -ani name of alphanumeric input file
   -udt name of user defined terrain input file
   -kml generate Google Earth (.kml) compatible output
   -geo generate an Xastir .geo georeference file (with .ppm output)
   -dbm plot signal power level contours rather than field strength
   -log copy command line string to this output file
 -gpsav preserve gnuplot temporary working files after SPLAT! execution
-metric employ metric rather than imperial units for all user I/O
-olditm invoke older ITM propagation model rather than the newer ITWOM
The command-line options for splat and splat-hd are identical. The -log command line switch causes all invoked command line options to be logged to a file of your choosing (logfile.txt):

splat -t tx_site -r rx_site -s nj_cities -o topo_map -log logfile.txt

SPLAT! operates in two distinct modes: point-to-point mode, and area prediction mode. Either a line-of-sight (LOS) or Irregular Terrain (ITM) propagation model may be invoked by the user. True Earth, four-thirds Earth, or any other user-defined Earth radius may be specified when performing line-of-sight analysis.

POINT-TO-POINT ANALYSIS
SPLAT! may be used to perform line-of-sight terrain analysis between two specified site locations. For example:

splat -t tx_site.qth -r rx_site.qth

invokes a line-of-sight terrain analysis between the transmitter specified in tx_site.qth and receiver specified in rx_site.qth using a True Earth radius model, and writes a SPLAT! Path Analysis Report to the current working directory. The report contains details of the transmitter and receiver sites, and identifies the location of any obstructions detected along the line-of-sight path. If an obstruction can be cleared by raising the receive antenna to a greater altitude, SPLAT! will indicate the minimum antenna height required for a line-of-sight path to exist between the transmitter and receiver locations specified. Note that imperial units (miles, feet) are specified unless the -metric switch is added to SPLAT!'s command line options:

splat -t tx_site.qth -r rx_site.qth -metric

If the antenna must be raised a significant amount, this determination may take a few moments. Note that the results provided are the minimum necessary for a line-of-sight path to exist, and in the case of this simple example, do not take Fresnel zone clearance requirements into consideration.

qth extensions are assumed by SPLAT! for QTH files, and are optional when specifying -t and -r arguments on the command-line. SPLAT! automatically reads all SPLAT Data Files necessary to conduct the terrain analysis between the sites specified. SPLAT! searches for the required SDF files in the current working directory first. If the needed files are not found, SPLAT! then searches in the path specified by the -d command-line switch:

splat -t tx_site -r rx_site -d /cdrom/sdf/

An external directory path may be specified by placing a ".splat_path" file under the user's home directory. This file must contain the full directory path of last resort to all the SDF files. The path in the $HOME/.splat_path file must be of the form of a single line of ASCII text:

/opt/splat/sdf/

and can be generated using any text editor.

A graph of the terrain profile between the receiver and transmitter locations as a function of distance from the receiver can be generated by adding the -p switch:

splat -t tx_site -r rx_site -p terrain_profile.png

SPLAT! invokes gnuplot when generating graphs. The filename extension specified to SPLAT! determines the format of the graph produced. .png will produce a 640x480 color PNG graphic file, while .ps or .postscript will produce postscript output. Output in formats such as GIF, Adobe Illustrator, AutoCAD dxf, LaTeX, and many others are available. Please consult gnuplot, and gnuplot's documentation for details on all the supported output formats.

A graph of elevations subtended by the terrain between the receiver and transmitter as a function of distance from the receiver can be generated by using the -e switch:

splat -t tx_site -r rx_site -e elevation_profile.png

The graph produced using this switch illustrates the elevation and depression angles resulting from the terrain between the receiver's location and the transmitter site from the perspective of the receiver's location. A second trace is plotted between the left side of the graph (receiver's location) and the location of the transmitting antenna on the right. This trace illustrates the elevation angle required for a line-of-sight path to exist between the receiver and transmitter locations. If the trace intersects the elevation profile at any point on the graph, then this is an indication that a line-of-sight path does not exist under the conditions given, and the obstructions can be clearly identified on the graph at the point(s) of intersection.

A graph illustrating terrain height referenced to a line-of-sight path between the transmitter and receiver may be generated using the -h switch:

splat -t tx_site -r rx_site -h height_profile.png

A terrain height plot normalized to the transmitter and receiver antenna heights can be obtained using the -H switch:

splat -t tx_site -r rx_site -H normalized_height_profile.png

A contour of the Earth's curvature is also plotted in this mode.

The first Fresnel Zone, and 60% of the first Fresnel Zone can be added to height profile graphs by adding the -f switch, and specifying a frequency (in MHz) at which the Fresnel Zone should be modeled:

splat -t tx_site -r rx_site -f 439.250 -H normalized_height_profile.png

Fresnel Zone clearances other 60% can be specified using the -fz switch as follows:

splat -t tx_site -r rx_site -f 439.250 -fz 75 -H height_profile2.png

A graph showing ITM path loss may be plotted using the -l switch:

splat -t tx_site -r rx_site -l path_loss_profile.png

As before, adding the -metric switch forces the graphs to be plotted using metric units of measure. The -gpsav switch instructs SPLAT! to preserve (rather than delete) the gnuplot working files generated during SPLAT! execution, allowing the user to edit these files and re-run gnuplot if desired.

When performing a point-to-point analysis, a SPLAT! Path Analysis Report is generated in the form of a text file with a .txt filename extension. The report contains bearings and distances between the transmitter and receiver, as well as the free-space and ITM path loss for the path being analyzed. The mode of propagation for the path is given as Line-of-Sight, Single Horizon, Double Horizon, Diffraction Dominant, or Troposcatter Dominant. Additionally, if the receiver is located at the peak of a single obstruction or at the peak of a second obstruction, SPLAT! will report RX at Peak Terrain Along Path when operating under the ITWOM propagation model.

Distances and locations to known obstructions along the path between transmitter and receiver are also provided. If the transmitter's effective radiated power is specified in the transmitter's corresponding .lrp file, then predicted signal strength and antenna voltage at the receiving location is also provided in the Path Analysis Report.

To determine the signal-to-noise (SNR) ratio at remote location where random Johnson (thermal) noise is the primary limiting factor in reception:

where T is the ERP of the transmitter in dBW in the direction of the receiver, NJ is Johnson Noise in dBW (-136 dBW for a 6 MHz television channel), L is the path loss provided by SPLAT! in dB (as a positive number), G is the receive antenna gain in dB over isotropic, and NF is the receiver noise figure in dB.

T may be computed as follows:

where TI is actual amount of RF power delivered to the transmitting antenna in dBW, GT is the transmitting antenna gain (over isotropic) in the direction of the receiver (or the horizon if the receiver is over the horizon).

To compute how much more signal is available over the minimum to necessary to achieve a specific signal-to-noise ratio:

where S is the minimum required SNR ratio (15.5 dB for ATSC (8-level VSB) DTV, 42 dB for analog NTSC television).

A topographic map may be generated by SPLAT! to visualize the path between the transmitter and receiver sites from yet another perspective. Topographic maps generated by SPLAT! display elevations using a logarithmic grayscale, with higher elevations represented through brighter shades of gray. The dynamic range of the image is scaled between the highest and lowest elevations present in the map. The only exception to this is sea-level, which is represented using the color blue.

Topographic output is invoked using the -o switch:

splat -t tx_site -r rx_site -o topo_map.ppm

The .ppm extension on the output filename is assumed by SPLAT!, and is optional.

In this example, topo_map.ppm will illustrate the locations of the transmitter and receiver sites specified. In addition, the great circle path between the two sites will be drawn over locations for which an unobstructed path exists to the transmitter at a receiving antenna height equal to that of the receiver site (specified in rx_site.qth).

It may desirable to populate the topographic map with names and locations of cities, tower sites, or other important locations. A city file may be passed to SPLAT! using the -s switch:

splat -t tx_site -r rx_site -s cities.dat -o topo_map

Up to five separate city files may be passed to SPLAT! at a time following the -s switch.

County and state boundaries may be added to the map by specifying up to five U.S. Census Bureau cartographic boundary files using the -b switch:

splat -t tx_site -r rx_site -b co34_d00.dat -o topo_map

In situations where multiple transmitter sites are in use, as many as four site locations may be passed to SPLAT! at a time for analysis:

splat -t tx_site1 tx_site2 tx_site3 tx_site4 -r rx_site -p profile.png

In this example, four separate terrain profiles and obstruction reports will be generated by SPLAT!. A single topographic map can be specified using the -o switch, and line-of-sight paths between each transmitter and the receiver site indicated will be produced on the map, each in its own color. The path between the first transmitter specified to the receiver will be in green, the path between the second transmitter and the receiver will be in cyan, the path between the third transmitter and the receiver will be in violet, and the path between the fourth transmitter and the receiver will be in sienna.

SPLAT! generated topographic maps are 24-bit TrueColor Portable PixMap (PPM) images. They may be viewed, edited, or converted to other graphic formats by popular image viewing applications such as xv, The GIMP, ImageMagick, and XPaint. PNG format is highly recommended for lossless compressed storage of SPLAT! generated topographic output files. ImageMagick's command-line utility easily converts SPLAT!'s PPM files to PNG format:

convert splat_map.ppm splat_map.png

Another excellent PPM to PNG command-line utility is available at: http://www.libpng.org/pub/png/book/sources.html. As a last resort, PPM files may be compressed using the bzip2 utility, and read directly by The GIMP in this format.

The -ngs option assigns all terrain to the color white, and can be used when it is desirable to generate a map that is devoid of terrain:

splat -t tx_site -r rx_site -b co34_d00.dat -ngs -o white_map

The resulting .ppm image file can be converted to .png format with a transparent background using ImageMagick's convert utility:

convert -transparent "#FFFFFF" white_map.ppm transparent_map.png

REGIONAL COVERAGE ANALYSIS
SPLAT! can analyze a transmitter or repeater site, or network of sites, and predict the regional coverage for each site specified. In this mode, SPLAT! can generate a topographic map displaying the geometric line-of-sight coverage area of the sites based on the location of each site and the height of receive antenna wishing to communicate with the site in question. A regional analysis may be performed by SPLAT! using the -c switch as follows:

splat -t tx_site -c 30.0 -s cities.dat -b co34_d00.dat -o tx_coverage

In this example, SPLAT! generates a topographic map called tx_coverage.ppm that illustrates the predicted line-of-sight regional coverage of tx_site to receiving locations having antennas 30.0 feet above ground level (AGL). If the -metric switch is used, the argument following the -c switch is interpreted as being in meters rather than in feet. The contents of cities.dat are plotted on the map, as are the cartographic boundaries contained in the file co34_d00.dat.

When plotting line-of-sight paths and areas of regional coverage, SPLAT! by default does not account for the effects of atmospheric bending. However, this behavior may be modified by using the Earth radius multiplier (-m) switch:

splat -t wnjt-dt -c 30.0 -m 1.333 -s cities.dat -b counties.dat -o map.ppm

An earth radius multiplier of 1.333 instructs SPLAT! to use the "four-thirds earth" model for line-of-sight propagation analysis. Any appropriate earth radius multiplier may be selected by the user.

When performing a regional analysis, SPLAT! generates a site report for each station analyzed. SPLAT! site reports contain details of the site's geographic location, its height above mean sea level, the antenna's height above mean sea level, the antenna's height above average terrain, and the height of the average terrain calculated toward the bearings of 0, 45, 90, 135, 180, 225, 270, and 315 degrees azimuth.

DETERMINING MULTIPLE REGIONS OF LOS COVERAGE
SPLAT! can also display line-of-sight coverage areas for as many as four separate transmitter sites on a common topographic map. For example:

splat -t site1 site2 site3 site4 -c 10.0 -metric -o network.ppm

plots the regional line-of-sight coverage of site1, site2, site3, and site4 based on a receive antenna located 10.0 meters above ground level. A topographic map is then written to the file network.ppm. The line-of-sight coverage area of the transmitters are plotted as follows in the colors indicated (along with their corresponding RGB values in decimal):

    site1: Green (0,255,0)
    site2: Cyan (0,255,255)
    site3: Medium Violet (147,112,219)
    site4: Sienna 1 (255,130,71)
    site1 + site2: Yellow (255,255,0)
    site1 + site3: Pink (255,192,203)
    site1 + site4: Green Yellow (173,255,47)
    site2 + site3: Orange (255,165,0)
    site2 + site4: Dark Sea Green 1 (193,255,193)
    site3 + site4: Dark Turquoise (0,206,209)
    site1 + site2 + site3: Dark Green (0,100,0)
    site1 + site2 + site4: Blanched Almond (255,235,205)
    site1 + site3 + site4: Medium Spring Green (0,250,154)
    site2 + site3 + site4: Tan (210,180,140)
    site1 + site2 + site3 + site4: Gold2 (238,201,0)

If separate .qth files are generated, each representing a common site location but a different antenna height, a single topographic map illustrating the regional coverage from as many as four separate locations on a single tower may be generated by SPLAT!.

PATH LOSS ANALYSIS
If the -c switch is replaced by a -L switch, an ITM path loss map, a field strength map, or a received power map for the transmitter site(s) specified may be generated. The type of analysis generated depends on the presence or absence of an -erp switch followed by a positive valued argument (or equivalent ERP entry in the appropriate .lrp file), or the presence or absence of the -dBm switch. The following example would generate an ITM path loss map:

splat -t wnjt -L 30.0 -s cities.dat -b co34_d00.dat -o path_loss_map

In this mode, SPLAT! generates a multi-color map illustrating expected signal levels in areas surrounding the transmitter site. A legend at the bottom of the map correlates each color with a specific path loss range in decibels.

The -db switch allows a threshold to be set beyond which contours will not be plotted on the map. For example, if a path loss beyond -140 dB is irrelevant to the survey being conducted, SPLAT!'s path loss plot can be constrained to the region bounded by the 140 dB attenuation contour as follows:

splat -t wnjt-dt -L 30.0 -s cities.dat -b co34_d00.dat -db 140 -o plot.ppm

The path loss contour threshold may be expressed as either a positive or negative quantity.

The path loss analysis range may be modified to a user-specific distance using the -R switch. The argument must be given in miles (or kilometers if the -metric switch is used). If a range wider than the generated topographic map is specified, SPLAT! will perform ITM path loss calculations between all four corners of the area prediction map.

The colors used to illustrate contour regions in SPLAT! generated coverage maps may be tailored by the user by creating or modifying SPLAT!'s color definition files. SPLAT! color definition files have the same base name as the transmitter's .qth file, but carry .lcf, .scf, and .dcf extensions. If the necessary file does not exist in the current working when SPLAT! is run, a file containing default color definition parameters that is suitable for manual editing by the user is written into the current directory.

When a regional ITM analysis is performed and the transmitter's ERP is not specified or is zero, a .lcf path loss color definition file corresponding to the transmitter site (.qth) is read by SPLAT! from the current working directory. If a .lcf file corresponding to the transmitter site is not found, then a default file suitable for manual editing by the user is automatically generated by SPLAT!.

A path loss color definition file possesses the following structure (wnjt-dt.lcf):

 ; SPLAT! Auto-generated Path-Loss Color Definition ("wnjt-dt.lcf") File
 ;
 ; Format for the parameters held in this file is as follows:
 ;
 ; dB: red, green, blue
 ;
 ; ...where "dB" is the path loss (in dB) and
 ; "red", "green", and "blue" are the corresponding RGB color
 ; definitions ranging from 0 to 255 for the region specified.
 ;
 ; The following parameters may be edited and/or expanded
 ; for future runs of SPLAT! A total of 32 contour regions
 ; may be defined in this file.
 ;
 ;
  80: 255, 0, 0
  90: 255, 128, 0
 100: 255, 165, 0
 110: 255, 206, 0
 120: 255, 255, 0
 130: 184, 255, 0
 140: 0, 255, 0
 150: 0, 208, 0
 160: 0, 196, 196
 170: 0, 148, 255
 180: 80, 80, 255
 190: 0, 38, 255
 200: 142, 63, 255
 210: 196, 54, 255
 220: 255, 0, 255
 230: 255, 194, 204

If the path loss is less than 80 dB, the color Red (RGB = 255, 0, 0) is assigned to the region. If the path loss is greater than or equal to 80 dB, but less than 90 db, then Dark Orange (255, 128, 0) is assigned to the region. Orange (255, 165, 0) is assigned to regions having a path loss greater than or equal to 90 dB, but less than 100 dB, and so on. Greyscale terrain is displayed beyond the 230 dB path loss contour. Adding the -sc switch will smooth the transitions between the specified quantized contour levels.

FIELD STRENGTH ANALYSIS
If the transmitter's effective radiated power (ERP) is specified in the transmitter's .lrp file, or expressed on the command-line using the -erp switch, field strength contours referenced to decibels over one microvolt per meter (dBuV/m) rather than path loss are produced:

splat -t wnjt-dt -L 30.0 -erp 46000 -db 30 -o plot.ppm

The -db switch can be used in this mode as before to limit the extent to which field strength contours are plotted. When plotting field strength contours, however, the argument given is interpreted as being expressed in dBuV/m.

SPLAT! field strength color definition files share a very similar structure to .lcf files used for plotting path loss:

 ; SPLAT! Auto-generated Signal Color Definition ("wnjt-dt.scf") File
 ;
 ; Format for the parameters held in this file is as follows:
 ;
 ; dBuV/m: red, green, blue
 ;
 ; ...where "dBuV/m" is the signal strength (in dBuV/m) and
 ; "red", "green", and "blue" are the corresponding RGB color
 ; definitions ranging from 0 to 255 for the region specified.
 ;
 ; The following parameters may be edited and/or expanded
 ; for future runs of SPLAT! A total of 32 contour regions
 ; may be defined in this file.
 ;
 ;
 128: 255, 0, 0
 118: 255, 165, 0
 108: 255, 206, 0
  98: 255, 255, 0
  88: 184, 255, 0
  78: 0, 255, 0
  68: 0, 208, 0
  58: 0, 196, 196
  48: 0, 148, 255
  38: 80, 80, 255
  28: 0, 38, 255
  18: 142, 63, 255
   8: 140, 0, 128

If the signal strength is greater than or equal to 128 dB over 1 microvolt per meter (dBuV/m), the color Red (255, 0, 0) is displayed for the region. If the signal strength is greater than or equal to 118 dBuV/m, but less than 128 dBuV/m, then the color Orange (255, 165, 0) is displayed, and so on. Greyscale terrain is displayed for regions with signal strengths less than 8 dBuV/m.

Signal strength contours for some common VHF and UHF broadcasting services in the United States are as follows:

       Analog Television Broadcasting
       ------------------------------
       Channels 2-6: City Grade: >= 74 dBuV/m
                        Grade A: >= 68 dBuV/m
                        Grade B: >= 47 dBuV/m
       --------------------------------------------
       Channels 7-13: City Grade: >= 77 dBuV/m
                        Grade A: >= 71 dBuV/m
                        Grade B: >= 56 dBuV/m
       --------------------------------------------
       Channels 14-69: Indoor Grade: >= 94 dBuV/m
                        City Grade: >= 80 dBuV/m
                        Grade A: >= 74 dBuV/m
                        Grade B: >= 64 dBuV/m
       Digital Television Broadcasting
       -------------------------------
       Channels 2-6: City Grade: >= 35 dBuV/m
                    Service Threshold: >= 28 dBuV/m
       --------------------------------------------
       Channels 7-13: City Grade: >= 43 dBuV/m
                    Service Threshold: >= 36 dBuV/m
       --------------------------------------------
       Channels 14-69: City Grade: >= 48 dBuV/m
                    Service Threshold: >= 41 dBuV/m
       NOAA Weather Radio (162.400 - 162.550 MHz)
       ------------------------------------------
                  Reliable: >= 18 dBuV/m
              Not reliable: < 18 dBuV/m
       Unlikely to receive: < 0 dBuV/m
       FM Radio Broadcasting (88.1 - 107.9 MHz)
       ----------------------------------------
       Analog Service Contour: 60 dBuV/m
       Digital Service Contour: 65 dBuV/m

RECEIVED POWER LEVEL ANALYSIS
If the transmitter's effective radiated power (ERP) is specified in the transmitter's .lrp file, or expressed on the command-line using the -erp switch, and the -dbm switch is invoked, received power level contours referenced to decibels over one milliwatt (dBm) are produced:

splat -t wnjt-dt -L 30.0 -erp 46000 -dbm -db -100 -o plot.ppm

The -db switch can be used to limit the extent to which received power level contours are plotted. When plotting power level contours, the argument given is interpreted as being expressed in dBm.

SPLAT! received power level color definition files share a very similar structure to the color definition files described earlier, except that the power levels in dBm may be either positive or negative, and are limited to a range between +40 dBm and -200 dBm:

 ; SPLAT! Auto-generated DBM Signal Level Color Definition ("wnjt-dt.dcf") File
 ;
 ; Format for the parameters held in this file is as follows:
 ;
 ; dBm: red, green, blue
 ;
 ; ...where "dBm" is the received signal power level between +40 dBm
 ; and -200 dBm, and "red", "green", and "blue" are the corresponding
 ; RGB color definitions ranging from 0 to 255 for the region specified.
 ;
 ; The following parameters may be edited and/or expanded
 ; for future runs of SPLAT! A total of 32 contour regions
 ; may be defined in this file.
 ;
 ;
   +0: 255, 0, 0
  -10: 255, 128, 0
  -20: 255, 165, 0
  -30: 255, 206, 0
  -40: 255, 255, 0
  -50: 184, 255, 0
  -60: 0, 255, 0
  -70: 0, 208, 0
  -80: 0, 196, 196
  -90: 0, 148, 255
 -100: 80, 80, 255
 -110: 0, 38, 255
 -120: 142, 63, 255
 -130: 196, 54, 255
 -140: 255, 0, 255
 -150: 255, 194, 204

ANTENNA RADIATION PATTERN PARAMETERS
Normalized field voltage patterns for a transmitting antenna's horizontal and vertical planes are imported automatically into SPLAT! when a path loss, field strength, or received power level coverage analysis is performed. Antenna pattern data is read from a pair of files having the same base name as the transmitter and LRP files, but with .az and .el extensions for azimuth and elevation pattern files, respectively. Specifications regarding pattern rotation (if any) and mechanical beam tilt and tilt direction (if any) are also contained within SPLAT! antenna pattern files.

For example, the first few lines of a SPLAT! azimuth pattern file might appear as follows (kvea.az):

        183.0
        0 0.8950590
        1 0.8966406
        2 0.8981447
        3 0.8995795
        4 0.9009535
        5 0.9022749
        6 0.9035517
        7 0.9047923
        8 0.9060051

The first line of the .az file specifies the amount of azimuthal pattern rotation (measured clockwise in degrees from True North) to be applied by SPLAT! to the data contained in the .az file. This is followed by azimuth headings (0 to 360 degrees) and their associated normalized field patterns (0.000 to 1.000) separated by whitespace.

The structure of SPLAT! elevation pattern files is slightly different. The first line of the .el file specifies the amount of mechanical beam tilt applied to the antenna. Note that a downward tilt (below the horizon) is expressed as a positive angle, while an upward tilt (above the horizon) is expressed as a negative angle. This data is followed by the azimuthal direction of the tilt, separated by whitespace.

The remainder of the file consists of elevation angles and their corresponding normalized voltage radiation pattern (0.000 to 1.000) values separated by whitespace. Elevation angles must be specified over a -10.0 to +90.0 degree range. As was the convention with mechanical beamtilt, negative elevation angles are used to represent elevations above the horizon, while positive angles represents elevations below the horizon.

For example, the first few lines a SPLAT! elevation pattern file might appear as follows (kvea.el):

        1.1 130.0
       -10.0 0.172
       -9.5 0.109
       -9.0 0.115
       -8.5 0.155
       -8.0 0.157
       -7.5 0.104
       -7.0 0.029
       -6.5 0.109
       -6.0 0.185

In this example, the antenna is mechanically tilted downward 1.1 degrees towards an azimuth of 130.0 degrees.

For best results, the resolution of azimuth pattern data should be specified to the nearest degree azimuth, and elevation pattern data resolution should be specified to the nearest 0.01 degrees. If the pattern data specified does not reach this level of resolution, SPLAT! will interpolate the values provided to determine the data at the required resolution, although this may result in a loss in accuracy.

EXPORTING AND IMPORTING REGIONAL CONTOUR DATA
Performing a regional coverage analysis based on an ITM path analysis can be a very time consuming process, especially if the analysis is performed repeatedly to discover what effects changes to a transmitter's antenna radiation pattern make to the predicted coverage area.

This process can be expedited by exporting the contour data produced by SPLAT! to an alphanumeric output (.ano) file. The data contained in this file can then be modified to incorporate antenna pattern effects, and imported back into SPLAT! to quickly produce a revised contour map. Depending on the way in which SPLAT! is invoked, alphanumeric output files can describe regional path loss, signal strength, or received signal power levels.

For example, an alphanumeric output file containing path loss information can be generated by SPLAT! for a receive site 30 feet above ground level over a 50 mile radius surrounding a transmitter site to a maximum path loss of 140 dB (assuming ERP is not specified in the transmitter's .lrp file) using the following syntax:

splat -t kvea -L 30.0 -R 50.0 -db 140 -ano pathloss.dat

If ERP is specified in the .lrp file or on the command line through the -erp switch, the alphanumeric output file will instead contain predicted field values in dBuV/m. If the -dBm command line switch is used, then the alphanumeric output file will contain receive signal power levels in dBm.

SPLAT! alphanumeric output files can exceed many hundreds of megabytes in size. They contain information relating to the boundaries of the region they describe followed by latitudes (degrees North), longitudes (degrees West), azimuths (referenced to True North), elevations (to the first obstruction), followed by either path loss (in dB), received field strength (in dBuV/m), or received signal power level (in dBm) without regard to the transmitting antenna's radiation pattern.

The first few lines of a SPLAT! alphanumeric output file could take on the following appearance (pathloss.dat):

        119, 117 ; max_west, min_west
        35, 34 ; max_north, min_north
        34.2265424, 118.0631096, 48.199, -32.747, 67.70
        34.2270358, 118.0624421, 48.199, -19.161, 73.72
        34.2275292, 118.0617747, 48.199, -13.714, 77.24
        34.2280226, 118.0611072, 48.199, -10.508, 79.74
        34.2290094, 118.0597723, 48.199, -11.806, 83.26 *
        34.2295028, 118.0591048, 48.199, -11.806, 135.47 *
        34.2299962, 118.0584373, 48.199, -15.358, 137.06 *
        34.2304896, 118.0577698, 48.199, -15.358, 149.87 *
        34.2314763, 118.0564348, 48.199, -15.358, 154.16 *
        34.2319697, 118.0557673, 48.199, -11.806, 153.42 *
        34.2324631, 118.0550997, 48.199, -11.806, 137.63 *
        34.2329564, 118.0544322, 48.199, -11.806, 139.23 *
        34.2339432, 118.0530971, 48.199, -11.806, 139.75 *
        34.2344365, 118.0524295, 48.199, -11.806, 151.01 *
        34.2349299, 118.0517620, 48.199, -11.806, 147.71 *
        34.2354232, 118.0510944, 48.199, -15.358, 159.49 *
        34.2364099, 118.0497592, 48.199, -15.358, 151.67 *

Comments can be placed in the file if they are preceeded by a semicolon. The vim text editor has proven capable of editing files of this size.

Note as was the case in the antenna pattern files, negative elevation angles refer to upward tilt (above the horizon), while positive angles refer to downward tilt (below the horizon). These angles refer to the elevation to the receiving antenna at the height above ground level specified using the -L switch if the path between transmitter and receiver is unobstructed. If the path between the transmitter and receiver is obstructed, an asterisk (*) is placed on the end of the line, and the elevation angle returned by SPLAT! refers the elevation angle to the first obstruction rather than the geographic location specified on the line. This is done in response to the fact that the ITM model considers the energy reaching a distant point over an obstructed path to be the result of the energy scattered over the top of the first obstruction along the path. Since energy cannot reach the obstructed location directly, the actual elevation angle to the destination over such a path becomes irrelevant.

When modifying SPLAT! path loss files to reflect antenna pattern data, only the last numeric column should be amended to reflect the antenna's normalized gain at the azimuth and elevation angles specified in the file. Programs and scripts capable of performing this task are left as an exercise for the user.

Modified alphanumeric output files can be imported back into SPLAT! for generating revised coverage maps provided that the ERP and -dBm options are used as they were when the alphanumeric output file was originally generated:

splat -t kvea -ani pathloss.dat -s city.dat -b county.dat -o map.ppm

Note that alphanumeric output files generated by splat cannot be used with splat-hd, or vice-versa due to the resolution incompatibility between the two versions of the program. Also, each of the three types of alphanumeric output files are incompatible with one another, so a file containing path loss data cannot be imported into SPLAT! to produce signal strength or received power level contours, etc.

USER-DEFINED TERRAIN INPUT FILES
A user-defined terrain file is a user-generated text file containing latitudes, longitudes, and heights above ground level of specific terrain features believed to be of importance to the SPLAT! analysis being conducted, but noticeably absent from the SDF files being used. A user-defined terrain file is imported into a SPLAT! analysis using the -udt switch:

splat -t tx_site -r rx_site -udt udt_file.txt -o map.ppm

A user-defined terrain file has the following appearance and structure:

       40.32180556, 74.1325, 100.0 meters
       40.321805, 74.1315, 300.0
       40.3218055, 74.1305, 100.0 meters

Terrain height is interpreted as being described in feet above ground level unless followed by the word meters, and is added on top of the terrain specified in the SDF data for the locations specified. Be aware that each user-defined terrain feature specified will be interpreted as being 3-arc seconds in both latitude and longitude in splat and 1 arc-second in latitude and longitude in splat-hd. Features described in the user-defined terrain file that overlap previously defined features in the file are ignored by SPLAT! to avoid ambiguity.

GROUND CLUTTER
The height of ground clutter can be specified using the -gc switch:

      splat -t wnjt-dt -r kd2bd -gc 30.0 -H wnjt-dt_path.png

The -gc switch as the effect of raising the overall terrain by the specified amount in feet (or meters if the -metric switch is invoked), except over areas at sea-level and at the transmitting and receiving antenna locations.

SIMPLE TOPOGRAPHIC MAP GENERATION
In certain situations it may be desirable to generate a topographic map of a region without plotting coverage areas, line-of-sight paths, or generating obstruction reports. There are several ways of doing this. If one wishes to generate a topographic map illustrating the location of a transmitter and receiver site along with a brief text report describing the locations and distances between the sites, the -n switch should be invoked as follows:

splat -t tx_site -r rx_site -n -o topo_map.ppm

If no text report is desired, then the -N switch is used:

splat -t tx_site -r rx_site -N -o topo_map.ppm

If a topographic map centered about a single site out to a minimum specified radius is desired instead, a command similar to the following can be used:

splat -t tx_site -R 50.0 -s NJ_Cities -b NJ_Counties -o topo_map.ppm

where -R specifies the minimum radius of the map in miles (or kilometers if the -metric switch is used). Note that the tx_site name and location are not displayed in this example. If display of this information is desired, simply create a SPLAT! city file (-s option) and append it to the list of command-line options illustrated above.

If the -o switch and output filename are omitted in these operations, topographic output is written to a file named tx_site.ppm in the current working directory by default.

GEOREFERENCE FILE GENERATION
Topographic, coverage (-c), and path loss contour (-L) maps generated by SPLAT! may be imported into Xastir (X Amateur Station Tracking and Information Reporting) software by generating a georeference file using SPLAT!'s -geo switch:

splat -t kd2bd -R 50.0 -s NJ_Cities -b NJ_Counties -geo -o map.ppm

The georeference file generated will have the same base name as the -o file specified, but have a .geo extension, and permit proper interpretation and display of SPLAT!'s .ppm graphics in Xastir software.

GOOGLE MAP KML FILE GENERATION
Keyhole Markup Language files compatible with Google Earth may be generated by SPLAT! when performing point-to-point or regional coverage analyses by invoking the -kml switch:

splat -t wnjt-dt -r kd2bd -kml

The KML file generated will have the same filename structure as a Path Analysis Report for the transmitter and receiver site names given, except it will carry a .kml extension.

Once loaded into Google Earth (File --> Open), the KML file will annotate the map display with the names of the transmitter and receiver site locations. The viewpoint of the image will be from the position of the transmitter site looking towards the location of the receiver. The point-to-point path between the sites will be displayed as a white line while the RF line-of-sight path will be displayed in green. Google Earth's navigation tools allow the user to "fly" around the path, identify landmarks, roads, and other featured content.

When performing regional coverage analysis, the .kml file generated by SPLAT! will permit path loss or signal strength contours to be layered on top of Google Earth's display along with a corresponding color key in the upper left-hand corner. The generated .kml file will have the same basename as that of the .ppm file normally generated.

DETERMINATION OF ANTENNA HEIGHT ABOVE AVERAGE TERRAIN
SPLAT! determines antenna height above average terrain (HAAT) according to the procedure defined by Federal Communications Commission Part 73.313(d). According to this definition, terrain elevations along eight radials between 2 and 10 miles (3 and 16 kilometers) from the site being analyzed are sampled and averaged for each 45 degrees of azimuth starting with True North. If one or more radials lie entirely over water or over land outside the United States (areas for which no USGS topography data is available), then those radials are omitted from the calculation of average terrain.

Note that SRTM-3 elevation data, unlike older USGS data, extends beyond the borders of the United States. Therefore, HAAT results may not be in full compliance with FCC Part 73.313(d) in areas along the borders of the United States if the SDF files used by SPLAT! are SRTM-derived.

When performing point-to-point terrain analysis, SPLAT! determines the antenna height above average terrain only if enough topographic data has already been loaded by the program to perform the point-to-point analysis. In most cases, this will be true, unless the site in question does not lie within 10 miles of the boundary of the topography data in memory.

When performing area prediction analysis, enough topography data is normally loaded by SPLAT! to perform average terrain calculations. Under such conditions, SPLAT! will provide the antenna height above average terrain as well as the average terrain above mean sea level for azimuths of 0, 45, 90, 135, 180, 225, 270, and 315 degrees, and include such information in the generated site report. If one or more of the eight radials surveyed fall over water, or over regions for which no SDF data is available, SPLAT! reports No Terrain for the radial paths affected.

ADDITIONAL INFORMATION
The latest news and information regarding SPLAT! software is available through the official SPLAT! software web page located at: http://www.qsl.net/kd2bd/splat.html.

AUTHORS

John A. Magliacane, KD2BD <kd2bd@amsat.org>
    Creator, Lead Developer

Doug McDonald <mcdonald@scs.uiuc.edu>
    Original Longley-Rice ITM Model integration

Ron Bentley <ronbentley@embarqmail.com>
    Fresnel Zone plotting and clearance determination