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  Estimating Path Loss on Marine Non-Line-of-Sight Paths

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Author Topic:   Estimating Path Loss on Marine Non-Line-of-Sight Paths
jimh posted 01-29-2009 08:09 AM ET (US)   Profile for jimh   Send Email to jimh  
Please use this discussion for any questions or comments concerning the path loss estimates derived in

Estimating Path Loss on Marine Non-Line-of-Sight Paths
http://continuouswave.com/whaler/reference/pathLoss.html

jimh posted 05-03-2009 11:05 AM ET (US)     Profile for jimh  Send Email to jimh     
Recently I came across a formula from an antenna manufacturer that gave an estimate of the increase in range that would result from changing to an antenna with 9-dB gain compared to an antenna with 6-dB gain. The formula predicted an increase in range by a factor of 1.32 times.

In any estimate of how range will increase with more signal, you must have some basis for assessing the path loss increase with distance. The rate of signal loss with increasing distance is obviously a crucial factor in determining how much farther you can communicate if you increase your signal by 3-dB.

If we use the free space theoretical model of path loss, 3-dB more signal will get you a much larger increase in range than if we use a more realistic model for path loss over real terrain on the real earth. So any claim for increase in range by adding 3-dB to the signal level is going to be entirely dependent on how much loss occurs with increasing distance in the path.

To cover this topic I have added two new sections to my article which examine this in detail. I also use the manufacturer's claims to deduce what sort of path loss they were assuming.

jimh posted 03-06-2011 02:14 PM ET (US)     Profile for jimh  Send Email to jimh     
In the summer of 2010 I had a chance to make a short test of the range of VHF Marine Band radio communication between my boat and another over open water. This occurred as we left Isle Royale in Lake Superior. About 14-miles out into the lake we called another boat who was still at the island. We were able to establish good communication with excellent signal-to-noise ratio. As it turned out, the other boat was not yet away from the dock, and his view to the lake was impeded by some intervening land mass of significant height. Thus our test was not entirely over open water.

A range of 14-miles boat-to-boat is below my estimate of 25-miles, which in the reference article I speculated may be possible. However, it was comforting to get confirmation that two rather ordinarily set-up boats could easily communicate by radio at a separation of 14-miles even with some intervening land obstacles in the radio path.

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