434 Mhz communication issue with boost electric fin on paddle board.

[zacksc]

A small company called Boost Surfing makes a small electric propeller that adds assistance and range to a stand up paddle board, extending its range kind of like an electric bike. It is pretty light weight (about 3 lbs) operates at about 24 volts. A 70 Wh battery, a small motor and propeller, and the controller and remote control receiver are all housed together in a waterproof enclosure that goes under the paddle board. On land the remote controller to start and stop the motor works great. When the board is in the water, the normal path for the on/off signal is a straight line directly from the remote control through the board to the motor assembly under the board. Apparently for carbon fiber boards, that normal signal path is mostly blocked. I have read vague comments that a small rope full of salt water can help the signal get around the board. That made me wonder if one could use metallic tape in some way to make an antenna that receives the 434 MHz signal on the deck of the the board and somehow conveys it to the underwater side of the board near the motor receiver. Does anyone know how to design or do this? Or does anyone have any ideas in general as to how to help the signal get to an underwater fin underneath a carbon fiber board?

I don't think it is hopeless. It is sort of at the edge or working. Like if you push the remote button 20 times with a new battery in the remote, it works maybe once. So I don't want to give up and I would most appreciative of expert advice. I don't really have any experience with antenna design beyond very basic physics concepts. I am thinking that the antenna would need to receive signal in the air at one end retransmit signal in the water very close to the device. Does that make any sense at all? Is that possible? I imagine the wavelength of 434 MHz is much shorter in water and the 1/e transmission length is maybe 10 centimeters or less? Any help will be appreciated!

 

[amberwolf]

That made me wonder if one could use metallic tape in some way to make an antenna that receives the 434 MHz signal on the deck of the the board and somehow conveys it to the underwater side of the board near the motor receiver. Does anyone know how to design or do this?

If you're really close to it, you can probably use "any" wire as an antenna, as long as it is directly connected to the antenna port on the unit.

If it works but not reliably, you may need to use a proper length / shape antenna, which you can design based on whatever onboard antenna it has (probably part of the PCB itself) mounted on top of the board, and then a shielded wire of the right impedance to go thru or around the board to the unit.

I don't remember enough of the math from my ham radio days, but there's plenty of info on how to design one, sizes, etc., out there. This is one possible search that finds useful info:
https://www.google.com/search?q=antenna+design+400mhz+range


BTW, the wavelenght itself can't change for a frequency, but the signal strength itself or it's absorption, reflection, etc does change with different materials (even the speed of propagation can change, as the "speed of light" is not constant everywhere (just consistent within a material).