Example Regional Coverage Analysis
In the previous post, I discussed how to use the Friis equation to determine the free space loss and receive level between a transmitter and receiver (Ref.1). The example was for an AIS Class B transmitter on a sailing yacht communicating with another boat at a distance of 10 nautical miles. Both boats have vertical whip antennas with gain of 3dBi, and transmission lines of 20m. The parameters were:
Pt = 2W = 2000mW = +33dBm
Freq = CH87B/88B = 161.975/162.025MHz = 162MHz approx.
Gt = Gr = 3dBi
Lt = Lr = 20m RG58/U = 8.1dB/100ft@200MHz = 5.3dB/20m approx.
R = 10 Nautical Miles = 18.52Km
Let’s use the Open Source Software program Splat! to solve for the transmitter LOS Line of Sight range and receive signal level. I discussed the basics of using Splat! in an earlier post (Ref.2). Let’s assume our blue water round the world yacht is located at the Toronto Harbourfront Spadina Quay and the antenna height is 15m above water level. Figure 1 shows the Latitude & Longitude. The additional parameters required by Splat:
Tx EIRP = 33dBm + 3dBi – 5.3 = 30.7dBm = 1175mW = 1.175W
TxERP = 30.7dBm – 2.15dB = 28.55dBm = 0.716W
Figures 2 & 3 show the QTH & LRP files required by Splat. Note that West Longitudes are positive in Splat. Figure 4 shows the Splat Windows interface for regional coverage. Figure 5 shows the Splat console output showing the Splat Data Files used.
Running Splat produces several files:
location.qth = Required Site Location Description (before)
location.lrp = Required Irregular Terrain Model parameters (before)
location.ppm = Splat Output Graphics File (after, open in Gimp)
location.kml = Splat Output KML Keyhole Markup Language File for Geographic Data (after, open in Google Earth)
Figure 6 shows the geometry of LOS Line of Sight from two antennas located 15m above the earth surface and with 4/3 Earth Radius:
Re=6371Km Average Earth Radius
d = 2*sqrt[((4/3)*Re+0.015)^2 – (4/3*Re)^2] = 31.9Km = 17.2Nmiles
Figure 7 shows the Splat value which is slightly lower 29.4Km, but this was for 301 N units.
In order to get the full flexibility of command line operation, Splat can be run on Linux. I use Ubuntu 20.04 running on VMWare Workstation 15 Player:
$sudo apt install splat
I setup a directory /splat where all the input & output files are stored. Within /splat I created a directory called sdf-sd where all the data files are stored. The qth and lrp files are created using a text editor gedit and each line is an entry exactly like the windows files. Figure 8 shows the command to perform a receive signal analysis:
splat – t spadina_quay -metric -L 15.0 -dbm -db -100 -o plot.ppm -kml -d ./sdf-sd
Note you have to specify where you located the data files by the -d switch. Figure 9 shows the receive level output as viewed on Google Earth.
#1. – “RF Signal Propagation Calculations – 1”, Blog Post
#2. – “Splat! RF Signal Propagation, Loss and Terrain Analysis Tool”, Blog Post
#3. – Splat Home Page
#4. – Splat Documentation
#5.– Splat with Windows GUI Version – Beta 1.1.2, Austin Wright