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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 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.

## References 