Author Topic: Does wifi work under water? A quick test..  (Read 878 times)

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Offline Emil

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Does wifi work under water? A quick test..
« on: June 09, 2019, 12:28:30 pm »
I was curious if wifi would work under water and I couldn't find any clear answer online, so I did a quick experiment.

I packed my phone in a plastic bag and notet the signal strength at different depts of water in a plastic bin. I placed the phone on a water filled cup, to make sure there was water on all sides. Water level under the phone 5cm, sides minimum 10cm. Depth is measured from under the phone, so allow ~2cm for thickness of phone and air in the bag.

Tests at 2.4GHz:
No water:   -54 dBm
On water filled cup:   -53 dBm
Water to top of cup (0cm):   -63 dBm
2cm   -57 dBm
3cm   -71 dBm
4cm   -79 dBm
5cm   -81 dBm
6cm   -85 dBm
7cm   -84 dBm
8cm   -85 dBm
9cm   -85 dBm

I didn't repeat the full series at 5GHz, but i measured -59dBm above water and -80dBm at 9cm.

It would be interesting to repeat this with an ESP32 under more controlled conditions..
 
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Offline rs20

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Re: Does wifi work under water? A quick test..
« Reply #1 on: June 09, 2019, 12:34:08 pm »
Try salting the water, would be interesting to see if increasing the conductivity makes the situation even worse.

To replicate sea water, start with 35 grams of salt to a beaker, and then add tap water until the total mass is 1,000 grams. (Says the internet, I haven't really verified that).

EDIT: This seems like a pretty clear answer: https://portail.telecom-bretagne.eu/publi/public/fic_download.jsp?id=20537

"The measurements demonstrate transmission capabilities of these low cost antennas to support 54 Mb/s WiFi underwater communications over short distances (25 cm in fresh water, 10 cm in sea water), using low emission power (10 dBm) and standards Wi-Fi modems."
« Last Edit: June 09, 2019, 12:44:47 pm by rs20 »
 

Offline ptricks

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Re: Does wifi work under water? A quick test..
« Reply #2 on: June 09, 2019, 12:35:59 pm »
Any radio in the 2-2.4Ghz range is a pretty bad performer through water because of the frequency that it uses.  Microwave ovens are around these frequencies ,the molecules in water interact with the waves to produce heat.  Low frequencies work best , submarines used ultra low frequencies for communication in water, and nature figured out long ago that low frequency is best, ie whale songs.

https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water
« Last Edit: June 09, 2019, 12:39:15 pm by ptricks »
 

Offline 3roomlab

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Re: Does wifi work under water? A quick test..
« Reply #3 on: June 09, 2019, 12:43:31 pm »
I remember reading that submarines use kHz to transmit thru water
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Offline rs20

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Re: Does wifi work under water? A quick test..
« Reply #4 on: June 09, 2019, 12:44:02 pm »
... and nature figured out long ago that low frequency is best, ie whale songs.

Conflating electromagnetics and acoustics?
 

Offline apis

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Re: Does wifi work under water? A quick test..
« Reply #5 on: June 09, 2019, 01:00:07 pm »
I remember reading that submarines use kHz to transmit thru water
Even lower I think (less than a kHz). Massive ground stations that transmit messages that the subs can receive even if a hundred meter under water.
 

Offline ptricks

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Re: Does wifi work under water? A quick test..
« Reply #6 on: June 09, 2019, 01:03:41 pm »
I remember reading that submarines use kHz to transmit thru water
Even lower I think (less than a kHz). Massive ground stations that transmit messages that the subs can receive even if a hundred meter under water.

They did use the low 3-300Hz range but I think the last sending station in the USA was closed a few years ago.
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Offline Monkeh

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Re: Does wifi work under water? A quick test..
« Reply #7 on: June 09, 2019, 01:05:42 pm »
I remember reading that submarines use kHz to transmit thru water
Even lower I think (less than a kHz). Massive ground stations that transmit messages that the subs can receive even if a hundred meter under water.

Down below 100Hz to do that. A few kHz for shallow communications at much higher (but still text only) speeds.
 

Offline Homer J Simpson

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Re: Does wifi work under water? A quick test..
« Reply #8 on: June 09, 2019, 01:24:57 pm »
Naval Communication Station Harold E. Holt

Exmouth, Western Australia

" The frequency is 19.8 kHz. With a transmission power of 1 megawatt, it is the most powerful transmission station in the Southern Hemisphere. "

https://en.wikipedia.org/wiki/Naval_Communication_Station_Harold_E._Holt


Jim Creek Naval Radio Station

Oso, Washington.

"  24.8 kHz with a power of 1.2 megawatts "

https://en.wikipedia.org/wiki/Jim_Creek_Naval_Radio_Station


The VLF communication to submarines is a very interesting read.

General VLF wiki ;

https://en.wikipedia.org/wiki/Very_low_frequency

You can also go to ELF ;

https://en.wikipedia.org/wiki/Extremely_low_frequency

« Last Edit: June 09, 2019, 01:31:26 pm by Homer J Simpson »
 

Offline soldar

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Re: Does wifi work under water? A quick test..
« Reply #9 on: June 09, 2019, 02:15:56 pm »
... ,the molecules in water interact with the waves to produce heat.

Next experiment: can I heat my coffee cup using my phone. :)

I wouldn't be surprised if there is already some similar hoax on YouTube.
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Online madires

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Online Alex Eisenhut

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Re: Does wifi work under water? A quick test..
« Reply #11 on: June 09, 2019, 02:30:30 pm »
I think there's already a ELF communication network of sorts in place: the 60Hz power grid.

I suppose you could signal the submerged subs by switching the entire state of New York on and off in Morse code.
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Offline apis

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Re: Does wifi work under water? A quick test..
« Reply #12 on: June 09, 2019, 02:58:40 pm »
I think there's already a ELF communication network of sorts in place: the 60Hz power grid.

I suppose you could signal the submerged subs by switching the entire state of New York on and off in Morse code.
Actually, I was thinking that maybe you could modulate the standard grid, although more subtly than using On-off keying, FSK/PSK perhaps.
« Last Edit: June 09, 2019, 03:07:09 pm by apis »
 

Offline NiHaoMike

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Re: Does wifi work under water? A quick test..
« Reply #13 on: June 09, 2019, 04:24:24 pm »
What might work and be surprisingly simple is to put an electrode in the water far from the shore (safety and to reduce energy lost in local current paths), then switch power to it via SCRs.
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Online tpowell1830

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Re: Does wifi work under water? A quick test..
« Reply #14 on: June 09, 2019, 09:57:08 pm »
Try this:


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Offline Homer J Simpson

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Re: Does wifi work under water? A quick test..
« Reply #15 on: June 09, 2019, 10:08:23 pm »

Russian ELF transmitter Zevs

http://www.vlf.it/zevs/zevs.htm
 

Offline tooki

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Re: Does wifi work under water? A quick test..
« Reply #16 on: June 10, 2019, 02:48:51 am »
That the 2GHz band is heavily absorbed by water is precisely why it’s used for microwave ovens (where this absorption makes it heat food) and for the ISM band allotted to unlicensed radio like WiFi and Bluetooth (where the absorption by atmospheric humidity limits functional range, allowing frequent reuse of frequencies and preventing someone from hogging a frequency over long distances).
 

Offline David Hess

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Re: Does wifi work under water? A quick test..
« Reply #17 on: June 11, 2019, 03:05:15 pm »
That the 2GHz band is heavily absorbed by water is precisely why it’s used for microwave ovens (where this absorption makes it heat food) and for the ISM band allotted to unlicensed radio like WiFi and Bluetooth (where the absorption by atmospheric humidity limits functional range, allowing frequent reuse of frequencies and preventing someone from hogging a frequency over long distances).

Liquid water absorption at RF frequencies is dominated by hydrogen bonding so there are no discrete peaks in absorption and all RF frequencies work about equally well with absorption gradually dropping off at lower frequencies.  5 GHz and 900 MHz microwave ovens work just as well as 2.4 GHz microwave ovens for heating water.  So will a VHF or UHF transmitter when properly coupled.

2.4 GHz is preferred because it is about the lowest frequency ISM band where a choke ring can be built into the door (1) which is too bad because 900 MHz microwave ovens were arguably superior except for their fragile door seal.

(1) This is why microwave oven doors are so thick yet can block the RF without a conductive seal.
 


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