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Underwater Transmitting - Recommended Frequency

R/C Submarine modelers

Postby Ramius-II » Wed May 14, 2003 11:09 am

I am looking for opinions and recommendations for the frequency and transmitter to send video back while the sub is submerged. I know the usual answer is 160 meters which seems like towing such a long wire would not be practical. ???

Thanks, Ed :D
Just one more wire!
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Postby M. Munger » Wed May 14, 2003 1:51 pm

Ed-
This is an area I've somewhat been working with lately. The best way to see what's going on down there is a hardwire to a monitor. Going wireless is frustrating: 2.4ghz and 900mhz broadcast power needed to penetrate water is very high (similar to the way a microwave oven works!), otherwise, you need to keep the antenna tip above the surface. Resolution, bandwidth etc, will also play a part.... Lower frequencies which will penetrate water readily are challenging to design/develop/implement with video/sound/data. Scott Thatcher (the "S" in H&S Video Periscopes) has very much 'been there and done that,' and imparted to me what little technical info I'm privy to. Cramming all of this into the confines of a functional R/C sub, another challenge. Tethering your transmitter antenna to a towed buoy does work successfully.

Any diver might then note that water clarity will be critical to seeing anything, no matter what the lux rating and resolution of your camera and or illumination via lighting. For pools it'll be a hoot, most ponds and lakes it'll likely look like mud.

Is it possible? #### yeah! Do it, figure out how to make it work, push the modeling/technical envelope. If it was easy, everybody'd have one....

I wish you much luck and perseverance

Matt
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Postby Ramius-II » Wed May 14, 2003 4:01 pm

Hi Matt:
Thanks for the input, 2.4 GHz is the resonant frequency of water which is why mircowave ovens operate there. 900 MHz might be a possibility. Mostly from what I've seen, the point of failure is in the antenna design. People try to use a "whip" or "rubber ducky" type at a lenght that produces negative gain. In the case of a whip, it needs a ground plane so the only way it will work is out of the water since the water is now the ground reference. Other designs allow for a power "gain" so if the design gives 3DB of gain you have doubled your ERP (Effective Radiated Power). Polarity plays a key part also. Weather it is vertical, horizontal or circular polarization. Maximum power is transfered when the transmitting antenna and the receiving antenna are in the same plane. In Model sub construction, we have a vertical antenna on our transmitter and our receiving antenna is horizontal in the hull, folded in a semicircle (which reduces it's capture area) so the receiver is only getting a few microvolts and yet we can operate servos. So it would make sense to me (unless they've changed the blend of the company coffee again) that transmitting should not be much of a problem. ??? I don't know for sure all the whys and limitations it just does not make sense to me that it's not possible. Of course if the end answer is you need at least 1000 watts of power, then I'll need a bigger battery. :D

Ed
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