sea communication - Problem

[memox]

hi, i have a problem about sea communication.

as show in figure, i want to make communication between two antennas. First antenna is over the sea, second antenna is over land or sea. between range of two antenna is 5 km.

according to you. Which frequency band can I use? Which is the best ?

 

[G4BCH]

I don't think that there is a 'best' frequency to use. You are operating over a line of sight path so, so long as you can overcome the path loss with an antenna that can be fitted to your offshore platform, it will work.
UHF is probably the most practical.

One thing to watch out for, is the height of your receive antenna, on a path like this with a reflection from part way along the path you could end up with no signal; it has been cancelled by the reflected wave. And then there is the tidal height variation to consider, that will alter the height at which the null will occur. You may need to consider diversity antennas at the shore end. Simple ray tracing will tell you if there is going to be a problem over this path and allow you to select a best height, or at least avoid the worst height for the shore antenna.

Peter

 

[artem]

sometimes, dependent on whether and frequency, it is possible to have good wave propagation even if no direct visibiity is there between antennas, yet it is not the case to rely on when making antennas for submarines.)

 

[vfone]

A good compromise between cost of equipment and performance, a good frequency for low power communication over water for 5km distance, is near 450MHz frequency range.
I am using successfully the 433MHz ISM band for a two way wireless communication link over the water (5km distance), using two Yagi antennas vertical polarized.