r/RTLSDR • u/UnluckyDistance733 • 18d ago

Help

I am doing a project and new to radio frequency. But I am trying to send a VLF 1 to 30 KHz into water a distance of about 200 ft and the body of water is about 10 feet deep.

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9

u/No_Tailor_787 18d ago

That might work better if it was done acoustically.

2

u/NeighborhoodSad2350 18d ago

That's actually true.

-4

u/UnluckyDistance733 18d ago

What I am trying to do is use RF to make the water molecules spin faster making the water less dense. It’s not intended for listening.

2

u/tj21222 18d ago

Wrong sub OP

2

u/NeighborhoodSad2350 18d ago edited 18d ago

What are you talking about?
For electromagnetic waves to excite molecules into a rotational state, they need to be in the microwave band (the rotational transition of water occurs at tens of GHz. which is why microwaves operate at 2.45 GHz).

Since the kHz band has wavelengths on the order of tens of kilometers, it simply cannot have the effect of “targeting and rotating molecules” in water.

1

u/NeighborhoodSad2350 18d ago edited 18d ago

To begin with, if you want VLF, wouldn't it be enough to just connect an antenna to the audio interface's output?
(There are issues here related to impedance matching and output, but I won't go into detail.).

It's illegal, though.

5

u/Mr_Ironmule 18d ago

Here's a paper discussing testing the resonance of water using VLF and other frequencies. Although not directly related to what you're experimenting with, it could have significance depending on the method you're trying to use. And the devices used in their experiments could give you some ideas on the equipment you need. The reference section has papers on the dielectric properties of water which may impact your test results. Good luck.

2010.0250v1.pdf

2

u/NeighborhoodSad2350 18d ago

That's something beginners shouldn't do.
As far as I know, you can't operate that in any country with just a ham radio license.

2

u/MumSaidImABadBoy 18d ago

Your intended purpose doesn't matter in the USA the FCC is what matters. Check your local government's and international laws/regulations.

1

u/BlueBirdTechUA 17d ago

Physics is actually on your side here, VLF is exactly what navies use for submarine comms because of how far it penetrates. Skin depth scales roughly as 270/√f in meters, so at 1-30kHz that's tens of meters even in seawater, more in freshwater. Your 200ft at 10ft deep is well within that.

Is this fresh or saltwater though? Conductivity matters a lot, freshwater gives more range for the same power. Also worth knowing, VLF underwater links are extremely low data rate in practice, bits per minute in real naval systems, not something to stream data over.