Introduction
In a recent post I was considering a hypothetical 2m amateur radio repeater and studying its VHF coverage with a Yagi antenna (Ref.1). In the process I read an article describing the difference in results of using the Longley-Rice & ITWOM propagation models (Ref2). The researchers used the Radio Mobile program developed by Roger Coudé VE2DBE (Ref.3). The program has an on line version (Ref.4) and stand alone version (Ref.5). I downloaded the stand alone version from Ian Brown G3TVU and quickly realized how comprehensive and detailed it is. There are excellent tutorials available, two of which I used. The first by K0LWC describes how to use the on line version (Ref.6) and the second by Double A Labs on how to use the stand alone desktop version (Ref.7).
In order to learn how to use the program, I compared results against previous work. In this post I will examine Marine VHF propagation for point to point links and general coverage with obstructions (Ref.8).
VHF Marine Regional Coverage
| AIS Parameter | Value |
| F=Frequency | 156 – 162MHz |
| Pt=Power | 25W = 44dBm |
| Rx Sensitivity | 0.22uVrms SINAD 12dB 0.71uVrms CH70 BER=1% |
| Gt=Tx Antenna Gain Gr=Rx Antenna Gain | 3dBi (Typically 0.9m long) 6dBi (Typically 2.4m long) |
| Antenna Height | 2.5m 5m 10m |
| Lt=Tx Coax Loss Lr=Rx Coax Loss RG-213 (2.7dB/100ft/200MHz) | 7.5m (0.7dB) 10m (0.9dB) 15m (1.3dB) |
| EIRP | 44+3-1.3=45.7dBm (3dBi Ant) 44+6-1.3=48.7dBm (6dBi Ant) |
In a previous post I looked at Marine VHF coverage and point to point range (Ref.8). Let’s examine this using Radio Mobile. For typical parameters, I am using an ICOM IC-M605 VHF transceiver (Ref.9). Figure 1 lists the parameters, with various antenna heights and gains.
Line of Sight & Earth Bulge
| Antenna Height m | Line of Sight d/2 |
| 2.5 | 6.5Km/3.5Nmi |
| 5 | 9.2Km/5Nmi |
| 10 | 13.0Km/7Nmi |
| 15 | 16.0Km/8.6Nmi |
| Re=6371Km |
Figure 2 shows a profile of ship to ship communication. Figure 3 lists the Line of Sight to the horizon for various antenna heights. For example, at 10m the horizon is 7Nmiles away.
Radio Mobile Configuration
Figures 4 & 5 show the various screens that have to be configured. The program standalone version from Ian Brown has a base network already configured which is really helpful to understand all the various features available. He has two spare folders Network 2 & Network 3 setup. I used Network 2 for my 2m repeater study and Network 3 for this study. Under Network Properties/Parameters, I defined the Net 3 to be Marine_VHF, with vertical polarization, freq 156-162MHz, mobile (50,90)% probability and Maritime over land for climate. Network Properties/Systems defines the Marine_VHF_Tx & Marine_VHF_Rx. Network Properties/Membership assigns them to Net 3 = Marine_VHF. Finally Unit Properties locates the Tx & Rx. I used the same locations as in the previous post (Ref.8).
Radio Mobile Point to Point
Figure 6 shows the same case as in Ref.8. We have antennas at 20m with gain of 10dBi (big antennas & high up!). For 0.22uVrms at the receiver, this translates to -120dBm. This gives a range of 101Km/55Nmi+ which is the same as before. Figure 7 shows a compromise of 6dBi antennas at 10m height. Range is 36Nmi. Finally Figure 8 shows 3dBi antennas at 2.5m height. Range is reduced to 15Nmi. What makes Radio Mobile so useful is the ease with which all these parameters can be changed and results seen instantly!
Radio Mobile Coverage
Figure 9 shows the area coverage for the case of 6dBi antenna at 10m. Note the strong signals as the ground level is reached and elevations increase removing the earth bulge.
Please send your comments, questions and suggestions to:
contact:
References
#1. – “Splat Antenna Patterns”
https://jeremyclark.ca/wp/telecom/splat-antenna-patterns/
#2. – “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
#3. – “Radio Mobile Home VE2DBE”
https://www.ve2dbe.com/english1.html
#4. – “Radio Mobile On Line”
https://www.ve2dbe.com/rmonline_s.asp
#5. – “Radio Mobile G3TVU Ian Brown”
http://www.g3tvu.co.uk/Radio_Mobile_Handbook.htm
#6. – “Radio Mobile Tutorial K0LWC”
https://www.youtube.com/watch?v=WJPPUk37jUA
#7. – “Radio Mobile Tutorial Double A Labs”
https://www.youtube.com/watch?v=UAEkNEQOMFE
#8. – “Splat! – Marine VHF Propagation”
https://jeremyclark.ca/wp/telecom/splat-marine-vhf-propagation/
#9. – “ICOM IC-M605 Marine Transceiver”
https://www.icomamerica.com/lineup/products/IC-M605/
