Does wifi work under water? A quick test.. - Page 1
Forum section: electronics / general

author: Emil
author_rank: Regular Contributor
timestamp: June 09, 2019, 12:28:30 pm
content: 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 dBmOn water filled cup: -53 dBmWater to top of cup (0cm): -63 dBm2cm -57 dBm3cm -71 dBm4cm -79 dBm5cm -81 dBm6cm -85 dBm7cm -84 dBm8cm -85 dBm9cm -85 dBmI 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..

author: rs20
author_rank: Super Contributor
timestamp: June 09, 2019, 12:34:08 pm
content: 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."

author: ptricks
author_rank: Frequent Contributor
timestamp: June 09, 2019, 12:35:59 pm
content: 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

author: rs20
author_rank: Super Contributor
timestamp: June 09, 2019, 12:44:02 pm
content: Quote from: ptricks on June 09, 2019, 12:35:59 pmConflating electromagnetics and acoustics?

author: apis
author_rank: Super Contributor
timestamp: June 09, 2019, 01:00:07 pm
content: Quote from: 3roomlab on June 09, 2019, 12:43:31 pmEven 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.

author: ptricks
author_rank: Frequent Contributor
timestamp: June 09, 2019, 01:03:41 pm
content: Quote from: apis on June 09, 2019, 01:00:07 pmThey did use the low 3-300Hz range but I think the last sending station in the USA was closed a few years ago.https://en.wikipedia.org/wiki/Project_Sanguine

author: Monkeh
author_rank: Super Contributor
timestamp: June 09, 2019, 01:05:42 pm
content: Quote from: apis on June 09, 2019, 01:00:07 pmDown below 100Hz to do that. A few kHz for shallow communications at much higher (but still text only) speeds.

author: Homer J Simpson
author_rank: Super Contributor
timestamp: June 09, 2019, 01:24:57 pm
content: Naval Communication Station Harold E. HoltExmouth, 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._HoltJim Creek Naval Radio StationOso, Washington." 24.8 kHz with a power of 1.2 megawatts "https://en.wikipedia.org/wiki/Jim_Creek_Naval_Radio_StationThe VLF communication to submarines is a very interesting read.General VLF wiki ;https://en.wikipedia.org/wiki/Very_low_frequencyYou can also go to ELF ;https://en.wikipedia.org/wiki/Extremely_low_frequency

author: soldar
author_rank: Super Contributor
timestamp: June 09, 2019, 02:15:56 pm
content: Quote from: ptricks on June 09, 2019, 12:35:59 pmNext experiment: can I heat my coffee cup using my phone.I wouldn't be surprised if there is already some similar hoax on YouTube.

author: madires
author_rank: Super Contributor
timestamp: June 09, 2019, 02:22:48 pm
content: https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 09, 2019, 02:30:30 pm
content: 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.

author: apis
author_rank: Super Contributor
timestamp: June 09, 2019, 02:58:40 pm
content: Quote from: Alex Eisenhut on June 09, 2019, 02:30:30 pmActually, I was thinking that maybe you could modulate the standard grid, although more subtly than using On-off keying, FSK/PSK perhaps.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 09, 2019, 04:24:24 pm
content: 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.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: June 09, 2019, 09:57:08 pm
content: Try this:

author: Homer J Simpson
author_rank: Super Contributor
timestamp: June 09, 2019, 10:08:23 pm
content: Russian ELF transmitter Zevshttp://www.vlf.it/zevs/zevs.htm

author: tooki
author_rank: Super Contributor
timestamp: June 10, 2019, 02:48:51 am
content: 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).

author: David Hess
author_rank: Super Contributor
timestamp: June 11, 2019, 03:05:15 pm
content: Quote from: tooki on June 10, 2019, 02:48:51 amLiquid 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.