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Old Feb 17, 2006, 10:45 AM
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Increasing Tx range underwater

I have read that R/C Submarines aren't able to go very deep due to the radio waves not being able to go very far through the water. What if a wire like what the full size subs use for sonar is trailed behind the sub? would this increase the depth that the R/C subs can go? Has this been tried before? and if so where can I read more about this?

Thanks for any help
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Old Feb 17, 2006, 11:54 AM
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Good idea, but unfortunately it won't help you much. The reason has to do with radio waves. Radio waves lose power (amplitude) as they travel distances. this is called Attenuation. Now Attenuation is affected by 2 things: the medium that the wave is going through, and the frequency of the signal. A radio wave loses power a whole lot more quickly in water than it does in air. (Like 10-100's of times faster.) So, that's why radios have limited range in water, because going through a few feet of water just totally nerfs the signals power, and the reciever can't pick it up. (The signal attenuates even faster in salt water than in fresh water- thus why you pretty much can't run RC subs in the ocean except if you have the antenna sticking out above the water.) Now, the other part that effects attenuation is the frequency of the signal. Low frequency signals tavel a whole lot better than high frequency signals. That explains why real subs can recieve signals under water- because they are sent to them at really low frequencies. This is impossible for remote control subs, because of a number of things. First, the length of the antenna would have to be miles long. In order for an antenna to work right, it has to be at least the wavelength of the signal. At the really low frequencies that travel well in water, this means that the antenna would literally have to be miles long. Second, you would have an incredible amount of delay between when you input a control, and when the sub responds. I won't get into the details of that, but at those frequencies it would take in the order of minutes for the sub to respond to a control input. Third, the government won't allow it. The FCC has all the frequencies from ultra low to ultra high mapped out and certain frequency ranges are mapped out to certain things. Why? So that interferance doesn't happen. If you have someone trying to control a radio control plane on a certain frequency, and a radio station is transmitting on the same frequency, the plane will think that the music is instructions for it and it'll start dancing and most certainly crash. (Ok, maybe it'll just start acting really wierd and crash.) So, you have to stay within the ranges that the FCC says you have to- namely 27 or 75 mHz. (For ground, airplanes run on 72 mHz radios.) You can increase the length of your antenna, but it will only help you if you have part of it sticking out of the water. (I would suggest keeping the length at a multiple of it's current length.)
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Last edited by d3snoopy; Feb 17, 2006 at 11:59 AM. Reason: darn typos
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Old Feb 17, 2006, 12:01 PM
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How deep do you want to go?
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Old Feb 17, 2006, 01:05 PM
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Thanks for the explaination. I was lookingto go no more than 10 feet or so
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Old Feb 17, 2006, 01:42 PM
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Quote:
Originally Posted by mrbaseballny
Thanks for the explaination. I was lookingto go no more than 10 feet or so
Standard radio gear will get you to at least double that without problems (in fresh water)
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Old Feb 17, 2006, 03:19 PM
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Quote:
Originally Posted by HelloMoto
Standard radio gear will get you to at least double that without problems (in fresh water)
Oh, alrighty then, I guess I'm set

Thanks for the help!!
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Old Feb 19, 2006, 06:58 AM
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This Australian radio amateur has researched the topic. Have a look at this page:

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