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Will a 49MHz transmission work underwater? Answered

I'm building a small device that needs to go to a depth of only a few feet in swimming pool water (I'd say three feet at the most) working on an arduino. I wanted to make it radio controlled and was planning on using a standard 49Mhz RC car circuit connected to the arduino. I don't want to keep the antenna above the water line and was wondering if a 49 MHz would work underwater. Any help would be appreciated. :)
I know higher frequencies like those in Bluetooth don't work underwater.

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KitemanBest Answer (author)2015-04-17

I found this on another forum:

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.

By my rough calculations, that means a 49MHz signal will penetrate (much attenuated) to a distance of around 3m/10'

However, your signal will not be travelling in a vertical line, but at an angle, so your target depth of 3' will probably be at the extreme.

You may want to take the route that is sometimes used by submarines, of having an antenna on a floating bouy, connected to the vessel by a length of cable.

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sidgupta (author)Kiteman2015-04-18
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Kiteman (author)sidgupta2015-04-18

You're welcome.

If you're going to keep your antenna underwater, don't forget to follow Downunder35m's advice for testing whether it will work.

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Downunder35m (author)2015-04-17

You can try but don't expect to use it at long distances.
Water is quite a good filter in this case.
If you have the RC cars still in working condition put it in a sealed bag and try it under water.

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BinuwaraB (author)Downunder35m2016-09-08

It is more efficient and simple.I'm also a newbie in making rc submarine can you please tell me a website for buying 49mhz remote controller

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iceng (author)2015-04-17

Your country is only one of three countries to own and operate a submarine alert ELF (Extremely_Low_Frequency) transmitter good to maybe 20 meters depth at 3 Hz

http://en.wikipedia.org/wiki/Communication_with_su...

All that gets transmitted is an alert code which tells a sub to rise to periscope depth and talk with a satellite to get detailed orders.

Like Kiteman said your 49 MHz will not get you a meter below sea water.

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Wired_Mist (author)2015-04-17

I'd make a floating antenna !

I know your not a big fan of that Idea but it will also give you and everyone around you where the (Rov?) is. Besides then you could use something like a 2.4Ghz signal and have room for expansion, like adding a Camera at the front !

Over a short distance you could also try experimenting with IR led's but I feel you would get a similar result as RF.

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