How to send frequency through water? - Page 1
Forum section: electronics / rf-microwave

author: Chriss
author_rank: Frequent Contributor
timestamp: November 10, 2019, 10:13:04 pm
content: Hi!Today I was talking with a friend of mine and we come to a theme about frequency transmitting, receiving and that stuff.We was also chatting about "how could be done" to send some frequency through water?What kind of transmitter would do that?I've assume a speaker is not suitable for that, maybe some sort of antenna?Does somebody have any knowledge/idea how to let's say send some signal through water, something like from the surface to adiver or so?Thanks for any info, maybe a link for something that could be reproduced at home for fun...My best regards.

author: WN1X
author_rank: Unknown
timestamp: November 10, 2019, 10:37:27 pm
content: What frequencies are you referring to? The classic solution for audio frequencies is to use a hydrophone for transmission and reception. These can cover from sub hertz to 240khz or so.

author: Chriss
author_rank: Frequent Contributor
timestamp: November 10, 2019, 10:42:20 pm
content: I don't know what frequency for now, but let's say something like several 100 Hz or so...But wait, is a hydrophone not a receiver?What about transmitting?This field is for me absolutely unknown.

author: radiolistener
author_rank: Super Contributor
timestamp: November 11, 2019, 02:23:55 pm
content: Submerged submarines using VLF band for two way communication from 10-20 meters depth, they are using several kilometers wire with buoy at the end as antenna. They have very active traffic on that band. You can listen them on 19-21 kHz frequency.At great depths submarine using ELF/SLF band. The U.S. Navy's system Seafarer operated at 76 Hz. The Russian system ZEVS operated at 82 Hz.Since ELF/SLF needs very long wire, submerged submarine cannot transmit, they are using it in receive only mode to listen commands from command center.Russians have special aircraft Тu-142MR (NATO classification "Bear-J") to communicate with submarines. It uses a very long wire, about 8600 meters length and can transmit commands to submarine. Interestingly, the system has a protection that cuts off the wire under high tension.US also have similar aircraft E-6 Mercury, which uses 7925 meters length wire as antenna.

author: radiolistener
author_rank: Super Contributor
timestamp: November 11, 2019, 02:34:22 pm
content: The main problem with ELF/SLF and VLF communication is that it needs very long antennas (many kilometers length). For ELF/SLF band it even more difficult. Because it needs many kilometers length antenna and very high power transmitter, because efficiency is too low. But ELF/SLF band allows to have communication through water at great depths

author: radiolistener
author_rank: Super Contributor
timestamp: November 11, 2019, 03:03:30 pm
content: Here you can find photo of such Russian aircraft antenna:https://defenceforumindia.com/forum/threads/tupolev-95-bear.71297/page-4

author: Chriss
author_rank: Frequent Contributor
timestamp: November 12, 2019, 12:30:40 am
content: Thanks for this infos, these are huge thinks, is there are something smaller what I could build to experiment in my aquarium or the river in front of my house?Something what I could build to send a signal and than receive them with a diy hydrophone?

author: Lord of nothing
author_rank: Super Contributor
timestamp: November 12, 2019, 12:49:48 am
content: What do the transmit? Something Like Morse? Voice?

author: radiolistener
author_rank: Super Contributor
timestamp: November 12, 2019, 04:17:53 am
content: Lord of nothing, they are using some kind of CW modulation, may be MSK or something like that. But their messages are encrypted, so you cannot read itHere is how it looks:

author: hamster_nz
author_rank: Super Contributor
timestamp: November 12, 2019, 04:36:01 am
content: Quote from: radiolistener on November 12, 2019, 04:17:53 amNice picture! - do you know what was used to receive that? (i.e. what was the antenna)Oh, and I wonder how many kW the transmitter on that plane is working at...

author: vk6zgo
author_rank: Super Contributor
timestamp: November 12, 2019, 04:40:00 am
content: We are talking at cross purposes.Acoustic waves (both tne ones you hear & higher) can fairly readily be transmitted through water.This is done by whales, dolphins, & some other marine creatures to communicate between individuals or between individuals & groups.It has also been done by various navies.The drawback for communications use is that normally it is fairly short range, so acoustic waves are much more often used for such things as echosounding, echolocation, & passive listening.In use, the acoustic wave is transmitted by a transducer which is fed with an electrical signal, & produces acoustic (sound) waves.(a similar function to a loudspeaker)It is received with another transducer (similar to a microphone).The other thing is receiving Radio waves under the sea.Seawater, particularly, acts as an "RF screen" to largely prevent the passage of electromagnetic waves, such as Radio.This increases with frequency, but is always present.Radio stations which can transmit through any reasonable depth of seawater use very low to extremely low frequencies & very high power.

author: radiolistener
author_rank: Super Contributor
timestamp: November 12, 2019, 04:57:45 am
content: Quote from: hamster_nz on November 12, 2019, 04:36:01 amjust long wire. But the signals are too weak, most of the time, there are interference and noises, so there is need to catch time when environment noises are not high.Quote from: hamster_nz on November 12, 2019, 04:36:01 amthey using onground transmitter, something like this:https://en.wikipedia.org/wiki/Goliath_transmitteraircraft VLF antennas are designed as backup channel. In case of Nuclear War, onground transmitter can be destroyed, so there is needs alternate way to communicate with submarinesZEVS transmitter power is about up to 7-14 megawatts

author: GerryR
author_rank: Frequent Contributor
timestamp: November 12, 2019, 12:00:31 pm
content: Principles of Underwater Sound by Robert Urick will probably tell you more than you want to know. This was the go-to book at the Naval Systems Underwater Sound Lab many (many) years ago. I believe it is still available used.

author: profdc9
author_rank: Frequent Contributor
timestamp: November 12, 2019, 08:10:45 pm
content: I think this depends on how deep you want to transmit under the water. I think the waves are absorbed within a fraction of a wavelength, so you may be able to get away with higher frequencies if you are transmitting to a fairly shallow depth.An alternative to a huge antenna if you want to broadcast with very low bandwidth is a loop antenna. Basically a very wide aluminum sheet (think aluminum roof flashing) with a capacitor (probably two large placed separated by HDPE rated for the high voltage, think same roof flashing) that resonates with a high Q. You couple to it using a smaller loop. The voltage across the loop can get very very high (tens of kV) if the antenna is efficient, and the fields near the antenna are also very high.

author: Lord of nothing
author_rank: Super Contributor
timestamp: November 12, 2019, 08:18:11 pm
content: What I know the just use an Floating Sat Antenna?!Theoretically the can deploy a Floating Sat Antenna think wo send after a period of Time a Message to a Sat.

author: MarkF
author_rank: Super Contributor
timestamp: November 13, 2019, 01:23:54 am
content: Quote from: GerryR on November 12, 2019, 12:00:31 pmYes. The "Bible" of underwater acoustics.We had several copies at work. However, they are very expensive ($80 USD in the '80s)!Quote from: vk6zgo on November 12, 2019, 04:40:00 amWe are talking about "propagation loss" here. And yes, it is directly proportional to frequency. The higher the frequency the higher the loss.There are three main travel paths for sound to travel between the transmitter and the receiver. They are "direct", "surface duct" and "bottom bounce" paths. All of which are depend on frequency, temperature profile, bottom depth, transmitter depth and receiver depth. There are also two distinct situations, deep water and shallow/littoral water, in which sound travel varies considerably.Quote from: Chriss on November 12, 2019, 12:30:40 amIf you want to experiment, I would think a swimming pool and a "cheap" modified marine fishfinder.Although, the fishfinder frequency would be quite high for long range communication.

author: Teledog
author_rank: Regular Contributor
timestamp: November 13, 2019, 03:43:26 am
content: Our local mfr. of dive confusers use ultrasonic (30-40kHz FSK) comms between their dive watches & tank/pressure transducer/monitors.I'm sure you could rig up a couple of cheap ultrasonic/piezo Rx/Tx units for short range use.{edit} with those freqs. might use a "bat listener" type circuit ie: up-converter/down-converter for voice comms.G'Luck!

author: EEVblog
author_rank: Unknown
timestamp: November 13, 2019, 04:24:29 am
content: https://en.wikipedia.org/wiki/Naval_Communication_Station_Harold_E._HoltPhoto with scale

author: EEVblog
author_rank: Unknown
timestamp: November 13, 2019, 04:28:12 am
content: Quote from: vk6zgo on November 12, 2019, 04:40:00 amThey are called Underwater Telephones, been around since WWII

author: vk6zgo
author_rank: Super Contributor
timestamp: November 13, 2019, 04:39:16 am
content: Quote from: EEVblog on November 13, 2019, 04:24:29 amFunny thing about scale---looking from the road, the building at the base of Tower One just looks like the "antenna tuning hut" at the base of an AM Broadcast station, until you stop to think that it is a BIG building & is 2-3 storeys high.