RF 27/433MHz maximum depth in pools (1-5 ppm chlorine, 6-8pH)

Hi guys,
i would like to discuess the issue of RF penetration in pool,
what is the dpeth i can count on when using a legel rf transmitter to an inwater robot ?
talking about an air distance of 10 meters and depth of up to 1.8m, can i count on transmitting and getting connectivity abovr 805 of the times in such scenarious?

i dont mind low baud rate.

There are a lot of factors involved:

- Frequency?

- Transmission power?

- Conductivity of pool water - can be quite high - (getting towards seawater if the pool is not drained much.)

- Grounded metal (railings, ladders etc)

- Glancing angle (i.e height above the water surface.

But generally transmission is OK judging from my experience at 40 and 458 Mhz, typical pools , typical transmitter powers etc.

David

about the frequency, this is part of my question, which do you think is best? is it 27Mhz
about saltines, lets say up to 3500ppm
About transmission power, what do you think is the power i need to transmit?
metals like a regular pool of cement with one ladder

the glancing angle, is it important? do you mean, it matters if im standing in the side of the pool, lets say 5 meters from it ( pool od 8mX4m and 1.8m deep) with the transmitter in hight of 30cm above the water or 200cm above the water ? is this the angle you mean? what is hte affect of it?

Have a look at the thread on here for some more information:

https://www.theassociationofmodelsubmariners.com/t1783-433-458-mhz-openlrs-in-a-swimming-pool?highlight=swimming

Sadly I don't think the link to the original paper by Butler works now But the paper was 1987!

Rob  in the Netherlands has some very good information and is developing some solutions:

https://www.robschuckman.nl/

Yes, you have the right idea. My use of the phrase glancing angle really refers to refraction and reflection at the water surface -  like light. But I haven't seen it creating any practical problems.

Power used has always been the legal limit for commercial equipment in the UK. (100mW, I think, but I have never measured it.)


David

Hi David
   27 mhz is the best frequency to use under water, probably using AM mod as standard radio control goes but as you go lower in frequency the more penetration you will get through the water, that's why i did low frequency using LF to get greater depth when sailing the big Gato as where i used to go it was about 90ft deep

   That is what i have been working on trying to get fully proportional control the same as what would be on say 27 mhz but i have done this now using ultra sonic's to control the sub so if it is salt water or fresh water it will still work. Transmitting end can knock out 60 watt's of ultra sonic if need be, it is on 40 khz. I have just done this to see if i can get it to work, unit can be switched to work in air or water it is not far off being finished should be interesting to see how it works out

   Did a lot of work to get antenna's to be resonant under water best mode AM 27MHZ also did LF antenna's to work under water. The antenna in the big sub tunes it self to the water it was in.

   Hope you find it as some interest Sub John

david f wrote:Have a look at the thread on here for some more information:

https://www.theassociationofmodelsubmariners.com/t1783-433-458-mhz-openlrs-in-a-swimming-pool?highlight=swimming

Sadly I don't think the link to the original paper by Butler works now But the paper was 1987!

Rob  in the Netherlands has some very good information and is developing some solutions:

https://www.robschuckman.nl/

Yes, you have the right idea. My use of the phrase glancing angle really refers to refraction and reflection at the water surface -  like light. But I haven't seen it creating any practical problems.

Power used has always been the legal limit for commercial equipment in the UK. (100mW, I think, but I have never measured it.)


David

I noticed something on that dutch site, where he says that RF regulations dont apply UNDER the water. if thats true then my idea of using a relay could be used with a standard 2.4ghz link to a low frequency RF transmitter under the water. Specifically, I'm thinking we could recycle a lot of 35mhz equipment. something like a buoy with a 35mhz module and antenna under the water with a 2.4ghz receiver attached. we could even go a step further by adding a conductivity switch so the 35mhz is only active when its in the water.


Another approach is just add coax to a 35mhz radio and have the antenna in the water so your not broadcasting "over the air"

Good point Geof.

It has always been in the back of my mind with this 27 MHz development  that OFCOM are not interested in ( under) water only Air!

John thanks for the info and congratulations but you need to give more detail. There is nothing here for us to work on.

David