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Old Oct 15, 2015, 08:03 PM
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How does the depth affect the signal with the sub and RC?

The questions in the title. I want to know the scientific reason to why and how the signal gets effected when you go deeper down in normal and salt water.

thanks in advance.
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Old Oct 16, 2015, 12:39 AM
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What research have you done? I am not a scientist, but have working knowledge and a very layman's view. The duh statement is water is much denser than air. So a signal that can go as far as you can see in air, you might get 15 - 20 feet in clear water. For the signals that do propagate through water (lower frequencies), like air the further away from the source of the signal the weaker it gets. Salt water has a lot of particulates dissolved in it and those absorb the signal quicker - like walking in the fog, you can not see very far because of all the moisture suspended in the air. A heavily chlorinated pool is one slightly better than salt water. Is this what you are asking about?
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Old Oct 16, 2015, 09:15 PM
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Some guys have run their subs as deep as 30 feet in a fresh water filled rock quarry. Scuba divers were alongside the subs and verified the depth.

In swimming pools, you can expect to have complete control down to a depth of 3-5 feet. The control depth depends on the chorine and other chemicals used to keep the water clean. If you get below the control depth you lose radio signal - and wait for the fail safe to activate an emergency surface.
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Old Oct 21, 2015, 11:41 AM
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Originally Posted by tchalfant View Post
What research have you done? I am not a scientist, but have working knowledge and a very layman's view. The duh statement is water is much denser than air. So a signal that can go as far as you can see in air, you might get 15 - 20 feet in clear water.
The density thing holds true for sound and pressure waves in general (i.e. SONAR). But is false for radio waves. It is only indicative that matter does attenuate radio waves and more of that SAME matter attenuates the radio waves even more. It's not enough to draw predict or draw conclusions about how well or why different types of matter attenuate radio waves.

However, apparently the density of lead does play a role into it's effectiveness of attenuating gamma rays, but apparently that's in tandem with a bunch of other factors and not just a result of density alone. it *sounds* like an issue of lead is already good at absorbing it and higher density means being able to "pack more of the same good stuff into a smaller area". I'm an engineer, not a physicist so this starts to go beyond the bounds of my knowledge and this paragraph here is the foggiest part of my entire post.

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Salt water has a lot of particulates dissolved in it and those absorb the signal quicker - like walking in the fog, you can not see very far because of all the moisture suspended in the air. A heavily chlorinated pool is one slightly better than salt water. Is this what you are asking about?
The particulates angle is also incorrect as well, or at least grossly over simplified.

Salt water is conductive and therefore attenuates radio signals similar to how a metal wall will. That's not to say pure water does not attenuate radio signals either- everything will. But conductivity is a real killer. It becomes conductive because salt which has the chemical formula of NaCL decomposes into Na+ and Cl- ions when dissolved in water. These ions are what conducts electricity and makes the water conductive. I am pretty sure similar Chlorine will do something similar when dissolved in water. Apparently, even a small amount of water molecules will also dissociate into H+ and HO- ions which causes water to be slightly conductive as well (and I mean very very slightly).

But if you take something like sugar, which will dissolve in water but NOT dissociate into ions , it will not cause the water to become conductive and significantly attenuate more radio waves more than pure water, even though it's also a particle floating in water.

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For the signals that do propagate through water (lower frequencies), like air the further away from the source of the signal the weaker it gets.
This is true, but should be generalized more to say that GENERALLY lower frequencies have better penetration and less multi-pathing issues than higher frequencies. However, different materials will pass different wavelengths differently and there can be particular "windows" of frequencies where a material will pass or block those wavelengths by unusual amounts.

The attenuation of electromagnetic radiation, or lack thereof is based on the atomic structure of the materials themselves and has no real or correlation with density, Different materials attenuate different wavelengths better or worse and unless you are able to see in the same wavelengths that your radio is using, using your eyes as an indicator is a poor substitute.

BTW, water is an unusually good absorber of 2.4GHz specifically. 2.4GHz is a higher frequency which generally works against penetration but that's not what I am talking about. Water molecules specifically absorb 2.4GHz in an exceptional amount compared to higher and lower frequencies. That's why it's used in microwaves to heat food. Don't use 2.4Ghz for subs. Don't use 5.8Ghz since it it has such poor penetration in general due to being a higher frequency.

It should also be noted that there seems to be multiple mechanisms responsible for how materials attenuate radio waves. They can be absorbed, scattered, or reflected by the atom. There's also the mechanism about why conductivity, in particular, will attenuate radio wave passing through a material which may or may not be a subset of one of the three previously mentioned mechanisms.
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Old Oct 22, 2015, 08:12 AM
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Thank you! I stand corrected.
Either way, the deeper you go, the further from the transmitter, the weaker the signal.
Dilan, we have not heard from you since you posted, has any of this answered your question?
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Old Oct 22, 2015, 09:31 AM
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I wonder if anyone has built an ELF station for their RC submarine yet?
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Old Oct 26, 2015, 03:33 PM
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I wonder if anyone has built an ELF station for their RC submarine yet?
I want to see them scale down the 1500 mile antenna.
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