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 Longley-Rice coverage analysis (feet/meters) (float)] [-p
terrain_profile.ext] [-e elevation_profile.ext] [-h height_profile.ext]
[-H normalized_height_profile.ext] [-l Longley-Rice_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] [-n]
[-N] [-nf] [-dbm] [-ngs] [-geo] [-kml] [-gpsav] [-metric]
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, Longley-Rice 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 Longley-Rice 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
Longley-Rice 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 data may be obtained
through anonymous FTP from:
ftp://e0srp01u.ecs.nasa.gov:21/srtm/version2/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.
The srtm2sdf utility may also be used to convert 3-arc second SRTM data
in Band Interleaved by Line (.BIL) format for use with SPLAT!. This
data is available via the web at:
http://seamless.usgs.gov/website/seamless/
Band Interleaved by Line data must be downloaded in a very specific
manner to be compatible with srtm2sdf and SPLAT!. Please consult
srtm2sdf’s documentation for instructions on downloading .BIL
topographic data through the USGS’s Seamless Web Site.
Even greater resolution and accuracy can be obtained by using 1 arc-
second SRTM-1 Version 2 topography data. This data is available for
the United States and its territories and possessions, and may be
downloaded from: ftp://e0srp01u.ecs.nasa.gov:21/srtm/version2/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.
LONGLEY-RICE PARAMETER (LRP) FILES
Longley-Rice 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. Longley-Rice 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 ; 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 Longley-Rice model. In this
example, SPLAT! will return the maximum path loss occurring 50% of the
time (fraction of time) in 90% of situations (fraction of situations).
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 these parameters, see:
http://flattop.its.bldrdoc.gov/itm.html and
http://www.softwright.com/faq/engineering/prop_longley_rice.html
The final parameter in the .lrp file corresponds to the transmitter’s
effective radiated power, 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 Longley-Rice 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://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://www.census.gov/geo/www/cob/co2000.html#ascii and
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! v1.3.0 Available Options... ]==--
-t txsite(s).qth (max of 4 with -c, max of 30 with -L)
-r rxsite.qth
-c plot coverage of TX(s) with an 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)
-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 filename 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
-gpsav preserve gnuplot temporary working files after SPLAT! execution
-metric employ metric rather than imperial units for all user I/O
The command-line options for splat and splat-hd are identical.
SPLAT! operates in two distinct modes: point-to-point mode, and area
prediction mode. Either a line-of-sight (LOS) or Longley-Rice
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 Longley-Rice 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 Longley-Rice
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.
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:
SNR = T - NJ - L + G - NF
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:
T = TI + GT
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:
Signal_Margin = SNR - S
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, a Longley-Rice path loss
map for a transmitter site may be generated:
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 Longley-
Rice 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 Longley-Rice 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.
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 a Longley-Rice 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 proceeded by a semicolon
character. 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
Longley-Rice 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. Note that the addition of ground clutter does not
necessarily modify the Longley-Rice path loss results unless the
additional clutter height results in a switch in the propagation mode
from a less obstructed path to a more obstructed path (from Line Of
Sight to Single Horizon Diffraction Dominant, for example). It does,
however, affect Fresnel zone clearances and line of sight
determinations.
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 in a semi-transparent manner. 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 Model integration
Ron Bentley <ronbentley@embarqmail.com>
Fresnel Zone plotting and clearance determination