I am looking to get a hold of small transmitters for use under water (sea water). They will be rigged to my sensor equipment and attached to fish for scientific monitoring, so size is very important.
The transmitters will need to:
- Transmit digital data packages of around 256 bits once per second.
- Have a minimum range of approx. 150 meters for good measure.
- Be able to work in an system with 10 or more active transmitters at the same time.
- Be as small as possible.
- Be as energy efficient as possible
My research indicates that my best bet is to build fixed frequency am-transmitters. (Availability, cost, size etc.) with small crystal oscillators. Is this a viable plan or are there better solutions out there?
Also, does anyone know if a setup like this could work under water? Keep in mind that I only need a range of 150 meters.
Since I only need a bitrate of about 512 bits / second per transmitter (I want overhead for more data), would a lower frequency transmitter give me lower power consumption?
There are no size or power restrictions on the receivers.
EDIT: I am getting a lot of good information. The attenuation in sea water is much higher than I had expected, thanks for the graph.
I see that even my initial plan, using frequencies in the LF-band is out of reach at this range.
1KHz at 20 meters range with more receivers placed seems more realistic, but even this does not look very promising. It seems that EM transmission just isn't that feasible under sea water. Maybe I'll be better off with an acoustic transmitter or some form of passive telemetry.
Thank you all.