5 ms·

How well does radio transmission work under water?

eimrine 4y ago
Typically 3-4m, 7m peak depth.
yardie 4y ago
Doesn’t work on any unlicensed frequencies. 2.4Ghz and 5Ghz are absorbed by water. Militeary submarines use VLF frequencies. With a mile long antenna. So tether is the only real practical method.
- jacquesm 4y ago
  No idea why this got downvoted, it is 100% accurate.
  - BugsJustFindMe 4y ago
    It's not 100% accurate to say that tether is the only practical method. Untethered AUV/UUVs are quite common in the industry.
    - yardie 4y ago
      Please point them out. All the UUVs/AUVs I've found are either tethered to a buoy or completely autonomous and only transmit when the surface. In all practicality there is no completely untethered ROV on the market. Acoustic controlled UUVs are still line of sight.
- vbezhenar 4y ago
  What about sound?
  - yardie 4y ago
    They operate at 100s of bits per second not fast enough to transmit live video so your back to line of sight.
  - BugsJustFindMe 4y ago
    Acoustic modems are indeed common in underwater applications.
skyeto 4y ago
Terrible (for 2.4/5GHz). They seemed to have worked around there not being a lot of hobbyist receivers by buying toy submarines that use lower frequencies like 40MHz and used the boards from there, nifty but seems very limited. https://brickexperimentchannel.wordpress.com/2022/07/13/rc-submarine-4-0-radio-7-10/ https://brickexperimentchannel.wordpress.com/2022/07/13/rc-s...
BugsJustFindMe 4y ago
Very poorly. The 27MHz radio used here won't penetrate more than a meter or so. GPS doesn't work through more than some inches. But like most things, the lower the frequency and higher the amplitude the farther the penetration. Acoustic modems work better under realistic constraints, though with a few exceptions you need the line of communication to be rather vertical if you're talking very long distances (hundreds or thousands of meters) because the speed of sound in water varies by pressure/temperature/salinity so the signal path curves up back toward the surface (from Snell's law).
- jstanley 4y ago
  Maybe the antenna could be on a long thin wire with a float so that it is always at the surface?
  - dylan604 4y ago
    what happens when it submerges lower than the radio buoy's tether?
    - jstanley 4y ago
      Then the antenna is submerged, but just make the tether as long as the maximum intended depth. You can't go infinitely deep anyway, because eventually the pressure will penetrate the seals.
      - BugsJustFindMe 4y ago
        > You can't go infinitely deep anyway, because eventually the pressure will penetrate the seals. This is actually the least useful reason why you can't go infinitely deep. For exploration you will basically always want to be near the bottom of the body of water because mid column is just extremely boring, so you will want to make sure that your pressure tolerance allows for that. We just haven't found any infinitely deep bodies of water yet.
    - BugsJustFindMe 4y ago
contingencies 4y ago
Badly. https://www.globalsecurity.org/military/systems/ship/images/sub_a-05.gif https://www.globalsecurity.org/military/systems/ship/images/... https://www.aerodefensetech.com/component/content/article/adt/supplements/rfm/features/articles/17526 https://www.aerodefensetech.com/component/content/article/ad... https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/ar/1987/04/page05/index.html https://www.robkalmeijer.nl/techniek/electronica/radiotechni... Radio communication under the sea is not an attractive option for experiment by the radio amateur as it requires the use of very low frequencies, large antenna systems and very high powers. Fresh water lakes and rivers have much lower electrical conductivity than the sea and underwater transmission distances (or depths) up to 30 metres appear feasible using the [then-not-now] lowest frequency amateur band of 1.8 MHz. Even larger distances (or depths) could be achieved if a lower frequency band allocation were made available. However, that was written in 1987 and from a cursory historical review of https://en.wikipedia.org/wiki/ISM_radio_band https://en.wikipedia.org/wiki/ISM_radio_band it seems that exactly around the late 1980s time that article was written, the still earlier-suggested lower frequencies within the ISM bands were popularized and confirmed by various national regulators and there are now commercially available ISM-band transceivers available, eg. https://hoperf.com/modules/rf_transceiver/index.html https://hoperf.com/modules/rf_transceiver/index.html You can use directional (high dBi / high gain) antennae at one or both ends of the link, however this adds substantial complexity and generally negatively affects the vessel hydrodynamics. Let's say a sub delivering critical medicines to peoples in need is supposed to cross an ocean, it probably wants GPS at least sporadically (for inertial navigation error correction) and AIS (to avoid collisions with cargo ships in busy shipping channels) which means it's operating at least near-surface most of the time anyway which means a radio comms tower is likely the best option, and the question is moot. OTOH, if a sub is launched from a research vessel, it's cheaper and easier to use a tether. If it's just for a hobbyist, then the commercially available ISM transponders are likely adequate. So as per the 1987 comment: it seems in-water long distance comm's is really the domain of the military due to their unique requirement for deep-water stealth and the corresponding need for unlicensed low radio frequencies. For the rest of us, use ISM-band, a towed surface relay (also stealthy anyway), a tether, or just surface for comm's.

Typically 3-4m, 7m peak depth.

Doesn’t work on any unlicensed frequencies. 2.4Ghz and 5Ghz are absorbed by water. Militeary submarines use VLF frequencies. With a mile long antenna. So tether is the only real practical method.

jacquesm 4y ago
No idea why this got downvoted, it is 100% accurate.
- BugsJustFindMe 4y ago
  It's not 100% accurate to say that tether is the only practical method. Untethered AUV/UUVs are quite common in the industry.
  - yardie 4y ago
    Please point them out. All the UUVs/AUVs I've found are either tethered to a buoy or completely autonomous and only transmit when the surface. In all practicality there is no completely untethered ROV on the market. Acoustic controlled UUVs are still line of sight.
vbezhenar 4y ago
What about sound?
- yardie 4y ago
  They operate at 100s of bits per second not fast enough to transmit live video so your back to line of sight.
- BugsJustFindMe 4y ago
  Acoustic modems are indeed common in underwater applications.

skyeto 4y ago

Terrible (for 2.4/5GHz). They seemed to have worked around there not being a lot of hobbyist receivers by buying toy submarines that use lower frequencies like 40MHz and used the boards from there, nifty but seems very limited. https://brickexperimentchannel.wordpress.com/2022/07/13/rc-submarine-4-0-radio-7-10/ https://brickexperimentchannel.wordpress.com/2022/07/13/rc-s...

BugsJustFindMe 4y ago

Very poorly. The 27MHz radio used here won't penetrate more than a meter or so. GPS doesn't work through more than some inches. But like most things, the lower the frequency and higher the amplitude the farther the penetration. Acoustic modems work better under realistic constraints, though with a few exceptions you need the line of communication to be rather vertical if you're talking very long distances (hundreds or thousands of meters) because the speed of sound in water varies by pressure/temperature/salinity so the signal path curves up back toward the surface (from Snell's law).

jstanley 4y ago
Maybe the antenna could be on a long thin wire with a float so that it is always at the surface?
- dylan604 4y ago
  what happens when it submerges lower than the radio buoy's tether?
  - jstanley 4y ago
    Then the antenna is submerged, but just make the tether as long as the maximum intended depth. You can't go infinitely deep anyway, because eventually the pressure will penetrate the seals.
    - BugsJustFindMe 4y ago
      > You can't go infinitely deep anyway, because eventually the pressure will penetrate the seals. This is actually the least useful reason why you can't go infinitely deep. For exploration you will basically always want to be near the bottom of the body of water because mid column is just extremely boring, so you will want to make sure that your pressure tolerance allows for that. We just haven't found any infinitely deep bodies of water yet.
  - BugsJustFindMe 4y ago

contingencies 4y ago

Badly. https://www.globalsecurity.org/military/systems/ship/images/sub_a-05.gif https://www.globalsecurity.org/military/systems/ship/images/... https://www.aerodefensetech.com/component/content/article/adt/supplements/rfm/features/articles/17526 https://www.aerodefensetech.com/component/content/article/ad... https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/ar/1987/04/page05/index.html https://www.robkalmeijer.nl/techniek/electronica/radiotechni... Radio communication under the sea is not an attractive option for experiment by the radio amateur as it requires the use of very low frequencies, large antenna systems and very high powers. Fresh water lakes and rivers have much lower electrical conductivity than the sea and underwater transmission distances (or depths) up to 30 metres appear feasible using the [then-not-now] lowest frequency amateur band of 1.8 MHz. Even larger distances (or depths) could be achieved if a lower frequency band allocation were made available. However, that was written in 1987 and from a cursory historical review of https://en.wikipedia.org/wiki/ISM_radio_band https://en.wikipedia.org/wiki/ISM_radio_band it seems that exactly around the late 1980s time that article was written, the still earlier-suggested lower frequencies within the ISM bands were popularized and confirmed by various national regulators and there are now commercially available ISM-band transceivers available, eg. https://hoperf.com/modules/rf_transceiver/index.html https://hoperf.com/modules/rf_transceiver/index.html You can use directional (high dBi / high gain) antennae at one or both ends of the link, however this adds substantial complexity and generally negatively affects the vessel hydrodynamics. Let's say a sub delivering critical medicines to peoples in need is supposed to cross an ocean, it probably wants GPS at least sporadically (for inertial navigation error correction) and AIS (to avoid collisions with cargo ships in busy shipping channels) which means it's operating at least near-surface most of the time anyway which means a radio comms tower is likely the best option, and the question is moot. OTOH, if a sub is launched from a research vessel, it's cheaper and easier to use a tether. If it's just for a hobbyist, then the commercially available ISM transponders are likely adequate. So as per the 1987 comment: it seems in-water long distance comm's is really the domain of the military due to their unique requirement for deep-water stealth and the corresponding need for unlicensed low radio frequencies. For the rest of us, use ISM-band, a towed surface relay (also stealthy anyway), a tether, or just surface for comm's.