# Achieving a transmission data underwater at 100 mts depth

##### Well-Known Member
Ever wonder about communication with submarines? I know aircraft have been used, all you do is get above the sub area and deploy a long wire antenna, about six miles long. Pretty simple huh? Communication at a depth of 100 meters is not going to be easy, even wired. Figure roughly atmospheric pressure is about 14.6 PSI. That pressure increases about 1 atmosphere for every 10 meters so at about a depth of 100 meters that is about 146 PSI or 10 atmos of pressure on whatever is down there. Tethered maybe to a surface buoy may work.

Ron

#### dknguyen

##### Well-Known Member
Ever wonder about communication with submarines? I know aircraft have been used, all you do is get above the sub area and deploy a long wire antenna, about six miles long. Pretty simple huh? Communication at a depth of 100 meters is not going to be easy, even wired. Figure roughly atmospheric pressure is about 14.6 PSI. That pressure increases about 1 atmosphere for every 10 meters so at about a depth of 100 meters that is about 146 PSI or 10 atmos of pressure on whatever is down there. Tethered maybe to a surface buoy may work.

Ron
It's called a VLF drogue or trailing antenna. Imagine how careful you would have to be circling the aircraft so that you don't get tangled or caught up in your own antenna. A 30kHz, quarter wave antenna is 2500 meters. Lower frequencies are even longer so if your depth is only 100m, well...you might as well just use a cable rather than trailing out a 2500m long wire antenna behind your ship (as well as from your submerged device).

I'd go with a floating radio buoy at the surface connected to the submerged device with a data cable, personally.

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#### JPolo

##### New Member
Hi everyone! Thanks a lot for your responses. The main objectif with this project is to locate an object underwater, so the use of a cable is not an option. I did a deeper research on acoustics and I found an interesting technique for underwater localisation: Ultra-short baseline or USBL (https://en.wikipedia.org/wiki/Ultra-short_baseline). The problem is this technique requires the use of several hydrophones and transducers, wich are a little bit expensive (~$300-$400/each). By any chance, do you know any provider that would offer low-cost underwater acoustic stuff? (I've been checking on Benthowave.com but they don't show the prices and I've already send them an email; I'm waiting for their response).