Week 2: Module 1: 2/8/13
Yesterday we learned about how other ships can find the JRH. Today we will delve into how the JRH and others ships communicate with each other. The main method of communication that ships use is radio. We are all familiar with radios in cars and in our homes. These radios are different but work in a similar way. The main difference between these radios is that the ones in our homes only receive.
The radio on a ship is called a VHF (Very High Frequency) radio. This radio is an absolute necessity for ocean going ships. This is how ships communicate with each other and also with the shore when they are close enough. With the recent advances in satellite phones, however, this form of communication is becoming more and more prevalent on ocean going ships. While this technology is a great advance it is only useful if you know the phone number of the person or phone that you are trying to call.
The radio has a very similar history to radar and uses the same electromagnetic waves. The first radio signals were being transmitted in the late 1890’s and by the early 1900’s radio signals were being transmitted across the Atlantic. The way this works is illustrated in this the following image.
The VHF radios that are onboard ships function on a line of sight principle, basically if you can see it you can talk to it. There are exceptions to this, just like radar signals can bounce off of things and go other directions, sometimes you can talk to things that are out of sight. This works for the image above because they are transmitting from a fixed point to another fixed point and are often able to use a much higher power transmitter than on an ocean going vessel. With the combination of satellite technology and VHF radios todays ships are very well connected to the land.