SPLAT! A Terrestrial RF Path Analysis Application For Linux/Unix

Introduction

SPLAT! is an RF Signal Propagation, Loss, And Terrain analysis tool for the spectrum between 20 MHz and 20 GHz.

SPLAT! provides site engineering data such as the 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 and distances to known obstructions, path loss and field strength based on the Longley-Rice Irregular Terrain Model, and minimum antenna height requirements needed to establish line-of-sight communication paths and Fresnel Zone clearances absent of obstructions due to terrain.

SPLAT! produces reports, graphs, and highly detailed and carefully annotated topographic maps depicting line-of-sight paths, path loss, field strength, and expected coverage areas of transmitters and repeater systems. When performing line-of-sight analysis in situations where multiple transmitter or repeater sites are employed, SPLAT! determines individual and mutual areas of coverage within the network specified.

Applications of SPLAT! include site engineering, wireless network design, amateur radio communications, frequency coordination, communication system design, and terrestrial analog and digital television and radio broadcasting.

SPLAT! is free software. It may be redistributed and/or modified under the terms of the GNU General Public License Version 2 as published by the Free Software Foundation.

Download SPLAT!

Download SPLAT! and associated data files for your area through the following links:

SPLAT! Version 1.2.2 (splat-1.2.2.tar.bz2) (302k)
SRTM-3 Version 2 Elevation Models (for use with SPLAT! 1.1.1 and later versions)
1 Degree USGS Digital Elevation Models By Name
ARC/INFO Ungenerate (ASCII Format) Cartographic Boundary Files for County and County Equivalent Areas
ARC/INFO Ungenerate (ASCII Format) Cartographic Boundary Files for Census Designated Places

Documentation in both English and Spanish included with SPLAT! explains the meaning and use of these data files as well as general program operation. For areas within the United States, latitude and longitude information for specific locations can be determined through a street address through Google Geocode, Yahoo! Maps Web Services, and Geocode.com.

Note that SPLAT! uses coordinates based on WGS-84 or NAD83 datum. Older NAD27 coordinates can be converted to NAD83 coordinates using an on-line conversion utility.

An excellent command-line utility capable of converting the Portable PixMap (PPM) topographic map files generated by SPLAT! into highly compressed Portable Network Graphics (PNG) files is wpng. wpng may be downloaded from the libpng.org web site.

Thanks to work by John McMellen, a Windows version of SPLAT! is available.

SPLAT! News

SPLAT! Version 1.2.2 was released on May 10, 2008. This is mostly a bug-fix and accuracy improvement release.
SPLAT! Version 1.2.1 was released on October 20, 2007. This release has the ability to predict received signal strength levels based on transmitter effective radiated power, Longley-Rice path loss, and transmitter antenna radiation pattern. Path loss and field strength contours for networks containing as many as 30 transmitters, revised text reports, support for .BIL formatted topographic data, and increased integration with Google Earth are some of the many new features available in this release.
SPLAT! Version 1.2.0 was released on December 22, 2006. This release adds Fresnel Zone plotting and clearance determination, support for directional antenna systems (including the ability to import normalized azimuth and elevation antenna pattern data, pattern rotation, and mechanical beam tilt information into SPLAT!), and support for exporting Longley-Rice path loss contour studies outside of SPLAT! for the purpose of field analysis, or for external modification (with antenna pattern data, for example), and re-importing that data back into SPLAT! for rapid generation of updated contour maps. Also included are improved graphing functions, .geo Georeference Information File generation for compatibility with Xastir software, .kml Keyhole Markup Language file generation for compatibility with Google Earth, and support for metric as well as imperial units of measure.
SPLAT! Version 1.1.1 was released in April 2006. This release includes a new utility permitting use of Space Shuttle STS-99 Radar Topography Mission elevation data (SRTM-3 version 2) with SPLAT!. The increase in resolution and accuracy possible with this data over the older USGS data is quite significant. Additional coding changes were made that in concert with the new srtm2sdf utility should allow SPLAT! to function over all regions of the planet for which SRTM-3 elevation data is available.
SPLAT! version 1.1.0 was released on January 29, 2004. This version provides additional analysis results including path loss data, coverage maps, graphs, and reports based on the popular Longley-Rice Irregular Terrain propagation model.
SPLAT! Version 1.0.3 was released on Tuesday June 11, 2002. This version offers substantially faster analysis of transmitter and repeater regional service areas, and now provides a determination of antenna height above average terrain (HAAT), based on definitions and procedures outlined in FCC Part 73.313(d).
The Spring 2002 issue of CQ VHF magazine carried an article entitled, "A Computerized Analysis of VHF-and-Above, Free-Space Radio-Wave Propagation" that described some of the inner workings of SPLAT! software, and provided some examples of its use as a propagation visualization and terrain analysis tool.
Bill Walker, Ph.D., W5GFE, has created a SPLAT! server with a web-based interface.
Stan Horzepa, WA1LOU, discussed the use of SPLAT! in recent ARRLWeb feature articles Surfin': SPLAT That Path and Surfin': SPLAT That Path Online.

Who uses SPLAT!?

Interest in SPLAT! has been reported or demonstrated by:

The National Aeronautics and Space Administration (NASA) in developing communications link and fade margin policies for future lunar surface operations and exploration. See NASA's recent Technical Memorandum (PDF document) for details on SPLAT!'s application in exploring the "Final Frontier".
Lucent Technologies for use in designing wireless networks.
The United States Army for use in their Future Combat System (FCS).
Communications organizations such as Space Data Corporation.
Internet service providers such as Amigo.Net, who provide wireless access to clients.
Utility companies who employ wireless SCADA (Supervisory Control And Data Acquisition) networks for remote monitoring functions.
Commercial television broadcasters and viewers wishing to estimate broadcast range and reception requirements. Doug Lung's recent TVTechnology columns Do-it-Yourself Longley-Rice Studies, Determine Real Coverage with SPLAT! 1.2.0, and Running SPLAT On Windows describe the use of SPLAT! in estimating the range of over-the-air Digital Television broadcasts. Doug has also created a SPLAT! Resource web page to provide assistance in getting started with SPLAT!.
The University of Massachusetts in their Wireless Networking (CMPSCI 496A) course.
Amateur Radio Operators in estimating point-to-point link and repeater coverage. See the web sites of N0MAR/R, N2SMT/R, and K2MFF/R for some examples of SPLAT! in action.

Mapping Hacks (Tips and Tools for Electronic Cartography) published by O'Reilly and Associates includes a description of a somewhat older version of SPLAT! (Version 1.1.0), and provides some examples of its use beginning on page 73. A limited preview of the chapter describing SPLAT! use and operation can be viewed on-line through Google Books).

Program Operation

SPLAT! is invoked via the command-line, thereby permitting batch operations, or even background processing with user-defined priorities that can be performed either locally, or via remote workstations. Generated topographic maps are in the form of 24-bit (True Color) Portable Pixmap (PPM) image files that can be easily viewed and/or converted to other formats using standard Unix applications and utilities. Through gnuplot, SPLAT! generates terrain profile plots in GIF, PNG, Postscript, Adobe Illustrator, AutoCAD dxf, LaTeX, and many other formats supported by gnuplot. SPLAT! also generates obstruction and path-loss reports in the form of plain ASCII text.

The following are several examples of some of the data generated by SPLAT! Software:

Figure 1

Figure 1 is a thumbnail representation of a much higher resolution (2400x2430 pixel) repeater coverage map generated by SPLAT! software. Each color represents a discrete level of path loss based on the Longley-Rice irregular terrain propagation model, assuming a frequency of 439.250 MHz, horizontal polarization, and a receiver antenna height of 30 feet above ground level.

A legend at the bottom of the figure maps each color to a specific level of signal attenuation in dB. Effective coverage can be determined knowing the transmitter ERP, receiver noise figure, receiver antenna gain, frequency, bandwidth, and the minimum signal-to-noise ratio requirements.

Figure 2

In Figure 2, SPLAT! displays the line-of-sight coverage areas of four UHF-FM repeaters that are part of the W2NJR linked repeater system in New Jersey. Individual as well as mutual areas of coverage are clearly visible in this thumbnail image. Full resolution of this image is 3600x3600 pixels.

Figure 3

Figure 3 shows the line-of-sight paths between two transmitter sites and a common receiver site. In this example, the receiver is located 20 feet AGL in Oyster Bay, NY. The line-of-sight path between the Empire State Building and Oyster Bay is displayed in cyan, while the path between the Armstrong Tower in Alpine, NJ and Oyster Bay is displayed in green.

Line-of-sight conditions are absent for either path. An antenna at least 95 feet AGL is required to reach the Armstrong Tower. At least 82 feet of altitude is required to reach the Empire State Building over a line-of-sight path.

Figure 4

Figure 4 illustrates a point-to-point path profile generated by SPLAT! Version 1.2.0. In this example, normalized terrain heights referenced to the line-of-sight path between two tower sites are plotted as a function of distance from the receive site on the left. This plot shows a line-of-site path unobstructed by terrain clearly exists between the Lincroft and Lawrence Township sites. In addition, clearance of the first Fresnel zone is demonstrated. The Earth's curvature contour against which the terrain has been plotted is displayed at the base of the plot.

Figure 5

WFUT-TV 68's directional contour is illustrated in Figure 5 using SPLAT! Version 1.2.0. Although transmitting from New York City, WFUT's signal is directed west northwest toward Newark, New Jersey, the station's actual city of license.

Beginning with version 1.2.0, SPLAT! can generate KML files compatible with Google Earth when performing point-to-point analyses:

A line-of-sight path

Street-level path analysis

SPLAT! Google Earth Signal Strength Contours

Predicted WLIW-DT signal strength contours displayed in Google Earth (SPLAT! v1.2.1)

Google Earth's navigation tools allow the user to identify landmarks, roads, and other featured content.

In addition to graphic output, SPLAT! also produces data in the form of plain text. The following are a sample of some of the reports generated by SPLAT! software:

  
		--==[ SPLAT! v1.2.2 Path Analysis ]==--

-------------------------------------------------------------------------

Transmitter site: WLIW-DT
Site location: 40.7886 North / 73.4525 West (40° 47' 18" N / 73° 27' 9" W)
Ground elevation: 229.66 feet AMSL
Antenna height: 253.61 feet AGL / 483.27 feet AMSL
Antenna height above average terrain: 341.48 feet
Distance to Oyster Bay: 6.68 miles.
Azimuth to Oyster Bay: 324.60 degrees
Depression angle to Oyster Bay: -0.5824 degrees
Depression angle to the first obstruction: -0.5538 degrees

-------------------------------------------------------------------------

Receiver site: Oyster Bay
Site location: 40.8673 North / 73.5265 West (40° 52' 2" N / 73° 31' 35" W)
Ground elevation: 124.67 feet AMSL
Antenna height: 30.00 feet AGL / 154.67 feet AMSL
Distance to WLIW-DT: 6.68 miles
Azimuth to WLIW-DT: 144.55 degrees.
Elevation angle to WLIW-DT: +0.4858 degrees
Elevation angle to the first obstruction: +0.5896 degrees

-------------------------------------------------------------------------

Longley-Rice path calculation parameters used in this analysis:

Earth's Dielectric Constant: 15.000
Earth's Conductivity: 0.005 Siemens/meter
Atmospheric Bending Constant (N-units): 301.000 ppm
Frequency: 521.000 (MHz)
Radio Climate: 5 (Continental Temperate)
Polarization: 0 (Horizontal)
Fraction of Situations: 50.0%
Fraction of Time: 90.0%
Transmitter ERP: 92.000 kilowatts

-------------------------------------------------------------------------

Summary for the link between WLIW-DT and Oyster Bay:

WLIW-DT antenna pattern towards Oyster Bay: 0.390 (-8.18 dB)
Free space path loss: 107.43 dB
Longley-Rice path loss: 130.79 dB
Attenuation due to effects of terrain: 23.36 dB
Total path loss including WLIW-DT antenna pattern: 138.97 dB
Field strength at Oyster Bay: 72.27 dBuV/meter
Voltage produced by a terminated 50 ohm 0 dBd gain antenna: 311.48 uV
Voltage produced by a terminated 75 ohm 0 dBd gain antenna: 381.49 uV
Mode of propagation: Double Horizon, Diffraction Dominant

-------------------------------------------------------------------------

Between Oyster Bay and WLIW-DT, SPLAT! detected obstructions at:

        40.8609 N, 73.5204 W,  0.55 miles, 183.73 feet AMSL
        40.8590 N, 73.5187 W,  0.70 miles, 200.13 feet AMSL
        40.8578 N, 73.5176 W,  0.81 miles, 239.50 feet AMSL
        40.8548 N, 73.5147 W,  1.06 miles, 259.19 feet AMSL
        40.8487 N, 73.5090 W,  1.58 miles, 278.87 feet AMSL

Antenna at Oyster Bay must be raised to at least 98.00 feet AGL
to clear all obstructions detected by SPLAT!

Antenna at Oyster Bay must be raised to at least 245.00 feet AGL
to clear the first Fresnel zone.

Antenna at Oyster Bay must be raised to at least 185.00 feet AGL
to clear 60% of the first Fresnel zone.

  
      --==[ SPLAT! v1.2.2 Site Analysis Report For: WLIW-DT ]==--

---------------------------------------------------------------------------

Site location: 40.7886 North / 73.4525 West (40° 47' 18" N / 73° 27' 9" W)
Ground elevation: 229.66 feet AMSL
Antenna height: 253.61 feet AGL / 483.27 feet AMSL
Antenna height above average terrain: 341.48 feet

Average terrain at   0 degrees azimuth: 159.47 feet AMSL
Average terrain at  45 degrees azimuth: 222.70 feet AMSL
Average terrain at  90 degrees azimuth: 145.74 feet AMSL
Average terrain at 135 degrees azimuth: 64.72 feet AMSL
Average terrain at 180 degrees azimuth: 59.64 feet AMSL
Average terrain at 225 degrees azimuth: 97.26 feet AMSL
Average terrain at 270 degrees azimuth: 188.59 feet AMSL
Average terrain at 315 degrees azimuth: 196.19 feet AMSL

System Requirements

SPLAT! was developed on a 100 MHz Pentium-based PC having 16 megabytes of RAM and a 200 megabyte swap partition running under the Linux operating system (Slackware 9.0, 2.4.21 kernel). A faster processor and more memory, while recommended, are not necessary to operate SPLAT! comfortably over a 3 degree by 3 degree geographical region with 3 arc-second precision.