Naked Science Forum

General Science => General Science => Topic started by: neilep on 23/03/2007 18:22:06

Title: Radio Signals through water !!....how's that done then ?
Post by: neilep on 23/03/2007 18:22:06

My nephew just got his scuba qualification......which is nice !

So when he plumbs the depths of ocean luff and joy how does the radio communication frequency thing work ?

Do radio waves travel through water as well as they do in air ?

As a firm believer in empirical study I put my son with his walkie-talkie in the shower and it did not work very well at all !!..tch rch !!


So...how do scuba peeps talk to one another ?...and what about peeps who live in those undersea environments ?...is it all done via umbilical ?

Title: Radio Signals through water !!....how's that done then ?
Post by: another_someone on 23/03/2007 18:32:33

The whole point about scuba is that it is self contained (i.e. Self Contained Underwater Breathing Apparatus) - so, no umbilical cord.

My understanding was that most communication underwater, apart from hand singals, would only be ultrasonic transducers (sound travels very well in water, radio does not).

It is possible to receive radio underwater, but as I recall, it is limited to a fraction of a wavelength (e.g. half a wavelength), so a 10 metre signal would maybe be received about 5 metres underwater, while a 10Km wavelength, could be received at 5Km underwater.  A 10Km wavelength radio signal would have a frequency of about 30,000Hz - not a lot of bandwidth to send voice over.  Submarines can use these kinds of low frequencies to send and receive low signal rate digital signals, but you would not normally try and send voice or high data rate digital signals over it.

Title: Radio Signals through water !!....how's that done then ?
Post by: Pumblechook on 09/12/2007 00:25:14

Radio Waves penetrate very poorly through water and it gets worse with higher frequencies.  As someone said submarines use VLF or ELF..  Very or extra low frequency.  Even then they have to be near the surface. 

Try putting a glass bottle in front (between and it and the dish) of the Low Noise Block (thing at focus with wire coming from it) of a satellite dish,  It will have little effect.  Fill the bottle with water and the satellite signal will disappear. 

Title: Radio Signals through water !!....how's that done then ?
Post by: Pumblechook on 09/12/2007 22:15:07

Actually to with another thread about microwave ovens I tried putting sheets of wet paper in front of a satellite dish LNB and only 3 were needed (dry they add up to 0.3mm) to block the satellite sigmal but this at 12GHz. 

Title: Radio Signals through water !!....how's that done then ?
Post by: Pumblechook on 09/12/2007 22:17:56

Underwater Radio Communication


http://www.qsl.net/vk5br/UwaterComms.htm