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Splat! – Marine VHF Propagation

Introduction

In a 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). Let’s consider an example that I saw in a recent sailing forum. The discussion was around the range of a typical marine VHF transmitter using a quality VHF antenna mounted at 30 – 60ft above water level. These are the parameters based on Ref.2/3/4:

Pt = 25W = 25000mW = +44dBm
Freq = Marine Mid Band = 156 – 162MHz = 159MHz
Gt = Gr = 10dBi @ avg height = 20m
Lt = Lr = 25m RG213/U = 2.7dB/100ft(30.5m) @ 200MHz = 2.2dB/25m
EIRP=44+10-2.2=51.8dBm
ERP=51.8dBm-2.2dB=49.6dBm=91W
Prx=-13dBu for 12dB SINAD=-120dBm
Prx at Antenna=-120dBm-10+2.2=-127.8dBm

Splat! Receive Signal Power Plot

We can use the Splat! program to give receive power curves for a transmitter located south of Toronto on Lake Ontario with an ERP of 91W and antennas at 20 above the water. The limit of the -130dBm power curve is located at a receiver location of lake_ontarioE1 55Nmi away (Figure.2 power level color codes). A point to point Longley-Rice propagation test can also be run giving an Rx level of -130dBm.

Fig.1 VHF Tx at lake_ontarioW Rx at lake_ontarioE1
Fig.2 Splat! Receive Power Level Colors
Fig.3 Longley-Rice Propagation Parameters
Fig.4 YouTube Video Splat! – Marine VHF Propagation

References

#1. – “Splat! – RF Signal Propagation Calculations-2” , Blog Post

#2. – “ICOM M330G Marine VHF Transceiver Specifications”

#3. – “Shakespeare 476 Marine VHF Antenna”

#4. – “Belden 8267 Mil RG213/U Coaxial Cable”

#5. – “Splat! RF Signal Propagation, Loss and Terrain Analysis Tool”, Blog Post

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

#8. – Splat Documentation
http://www.qsl.net/kd2bd/splat.pdf

#9.– Splat with Windows GUI Version – Beta 1.1.2, Austin Wright
http://www.ve3ncq.ca/wordpress/?page_id=62

By Jeremy Clark

Jeremy Clark is a Senior Telecommunications Engineer and Advanced Amateur Radio Operator VE3PKC. He is the author of E-Books on Telecommunications, Navigation & Electronics.