Splat! – Antenna Patterns – Telecommunications, Navigation & Electronics

Introduction

Splat! (Ref.1) is a very versatile propagation prediction program that I discussed in several previous posts. In my first post, I looked at installation on Windows and Linux, how to obtain the digital elevation data files, create .qth & .lrp files, and run a simple point to point analysis (Ref.2). In the second and third posts I examined Marine VHF communications calculations for AIS & VHF coverage (Ref.3/4). The fourth post I did a path analysis for reception of VOR signals (Ref.5). In the last post I examined how we can use QGIS, an open source Geographic Information System, to analyze and convert various digital elevation data files so that they can be used with Splat! (Ref.6). Splat! requires SRTM 1arc_sec (30m) or 3arc_sec (90m) data files of type .hgt which can then be converted to .sdf splat data files by using the srtm2sdf converters.

In the last few years I have replaced my desktop and laptop, so I had to start with a new Splat! installation on both platforms. The original Splat! Linux build was 1.4.2, now it is 1.4.2-3build1. Installation is from the command line. I used the same Windows installation. I also re-downloaded the SRTM1sec/3sec data again from NASA Earth Data (Ref.7).

Fig.1 Latest Splat! Linux Build

Amateur Radio 2m 144MHz Base Station Coverage

Splat! Parameter	Value
F=Frequency	144MHz
Pt=Power	25W=14dBW 25W=25000mW=44dBm
Gt=Tx Antenna Gain SY250 VHF Antenna	7dBd (ref.dipole)
Lt=Tx Coax Loss	10m RG213/U (2.7dB/100ft) =0.9dB
ERP	14+7-0.9=20.1dBW=102.3W 44+7-0.9=50.1dBm

Fig.3 VE3PKC .lrp Parameters

Free Space Path Distance KM Freq=144MHz	Attenuation dB=32.44+ +20log10(F_MHz) +20log10(R_Km)
10Km	95.6dB
20Km	101.6dB
40Km	107.6dB
80Km	113.7dB
100Km	115.6

Fig.5 Free Space Attenuation at 144MHz

Hypothetically let’s say we want to study the coverage possibility of a 2m amateur radio base station. We can use my previous ve3pkc.qth file along with a suitable ve3pkc.lrp file. Figure 3 shows typical parameters for a 25W base station with a 7dBd Yagi and 10m of coax. Figure 4 shows the associated ve3pkc.lrp file . My location is now surrounded by cavernous condo buildings, so in reality this would be a terrible location, but for study purposes only.

Antenna Patterns .az .el

Fig.7 Excel Spreadsheet to Calculate Antenna .az Pattern

Fig.8 Excel Spreadsheet to Calculate Antenna .el Pattern

Figure 6 shows the horizontal and vertical patterns of a typical 2m Yagi antenna. The ve3pkc.az file starts with the azimuth of the main lobe which in this case is due East or 90deg. Then there is an entry for relative azimuths from 0deg to 360deg. The requirement is for normalized field voltage, so I read off the dB readings from the antenna pattern every 10deg and interpolated in between. Then I converted these to relative voltage by 10^(dB/20). After that I selected only the first two columns and pasted into a text reader and saved as ve3pkc.az.

I followed the same procedure for the ve3pkc.el file. The first line is the tilt angle and main azimuth. In this case 0deg and due East 90deg. Then the relative voltage over -10 to +90 deg. This is shown in Figure 8.

Longley Rice Path Loss Analysis Windows

Fig.9 Splat! Windows Longley Rice Path Loss Analysis

Fig.11 Path Loss Antenna .az & .el Files

For a Longley Rice path loss analysis using Splat! Windows, Figure 9 shows the setup. Figure 10 shows the result without .az or .el files. Figure 11 shows the result with both .az & .el files located in the working directory, thus taking into consideration the antenna patterns. Notice the increased attenuation off the main azimuth of 90deg/East.

ITWOM3 Path Loss Analysis

Fig.12 Linux Command Line for ITWOM3 Path Loss

Fig.14 Path Loss Antenna .az & .el Files

Figure 12 shows the Linux command line for a ITWOM3 path loss analysis. Figure 13 shows the result without .az or .el files. Figure 14 shows the result with both .az & .el files located in the working directory, thus taking into consideration the antenna patterns. Notice the increased attenuation off the main azimuth of 90deg/East.

Longley Rice vs. ITWOM3 Path Loss

Fig.15 P2P Graph Between Base Station & Test Site Port Hope Windows

Fig.16 P2P Graph Between Base Station & Test Site Port Hope Linux

Fig.17 Terrain Profile Port Hope to Base Station

Fig.18 Test Result Base Station to Port Hope Windows LR

Fig.19 Test Result Base Station to Port Hope Linux ITOW3

To compare the two path loss methods I selected a test site at Port Hope. The Longley Rice method gives a terrain shielding of 43dB, whereas the ITWOM3 gives only 11dB! – big difference. Ref.8 discusses the differences between the two models a topic for another post.

Fig.20 YouTube Video Splat! – Antenna Patterns

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References

#1. – Splat Home Page
http://www.qsl.net/kd2bd/splat.html

#2. – “Splat! RF Signal Propagation, Loss and Terrain Analysis Tool”
https://jeremyclark.ca/wp/telecom/splat-rf-signal-propagation-loss-and-terrain-analysis-tool/

#3. – “Splat!_RF Signal Propagation Calculations_2”
https://jeremyclark.ca/wp/telecom/rf-signal-propagation-calculations_splat/

#4. – “Splat! – Marine VHF Propagation”
https://jeremyclark.ca/wp/telecom/splat-marine-vhf-propagation/

#5. – “VOR VHF Omani-Directional Range – Splat! Path Analysis_a”
https://jeremyclark.ca/wp/telecom/vor-vhf-omni-directional-range-splat-path-analysis_a/

#6. – “Splat! – Digital Elevation Data with QGIS”
https://jeremyclark.ca/wp/telecom/splat-digital-elevation-data-with-qgis/

#7. – “NASA Earth Data”
https://search.earthdata.nasa.gov/search

#8. – “Comparison of Longley-Rice, ITM and ITWOM propagation models for DTV and FM broadcasting”, Stylianos Kasampalis et al,
https://www.researchgate.net/publication/250615289_Comparison_of_Longley-Rice_ITM_and_ITWOM_propagation_models_for_DTV_and_FM_broadcasting