Remember Oceangate Titan? Not pretty! Rating equipment for EXTERNAL pressure is a different ballgame to rating it for internal pressure, if you are wanting to send it to that depth. Neither is a trivial design nor construction, even if you are wanting to test the equipment inside a vessel. So unless you, personally, have the necessary qualifications and skill to design such a unit, may I suggest that you try to find someone who can. Depending on equipment size and your country, there will be regulatory authorities that will require inspections and certifications before it is commissioned. Stay safe!

Hi Doug. 
We are located in Melbourne and work with Bush Heritage in large reserve monitoring. Would love to chat and hear more about the issues you are having to see if we can help out with it. Let me know via private message and we can set up a meeting. 
Akiba

It's probably much easier to find a company selling acoustic modems than to try and create your own...very challenging environment to work within. I have about 10 years working with underwater acoustics (as a non-engineer). 

To give you the best advice, I need a bit more information about your specific application. Underwater communication typically relies on acoustic modems because radio waves don't travel well through water. For longer distances, a hybrid solution is often used. This could involve an acoustic modem transmitting data from your underwater sensor to a surface buoy or platform. The buoy could then relay the data to shore using traditional radio communication, such as 900MHz radios (even commercially available options like Ubiquiti radios, depending on distance and line-of-sight). To help me understand your needs and recommend the right approach, could you tell me more about:

Data Rate Requirements: How much data do you need to transmit, and how often?

Range: What is the vertical distance between your sensor and the surface receiver?

Environment: Are you working in shallow or deep water? What is the water temperature, salinity, and expected noise level?

Power Budget: How much power is available for the underwater sensor and modem?

Cost: What is your budget for the acoustic modem system?

Integration: How will you integrate the modem with your sensor and surface receiving system?

Real-time or Delayed: Do you need the data in real-time, or can it be stored and transmitted later?

Thank you for sharing! 

Hi Brett,

 

I am interested in developing really low cost multi channel underwater acoustic recorders.  Can you tell me a bit more about the board and stuff you were using for yours? You can get me at chris@wilcoanalytics.org.

 

Thanks,

 

Chris

Really great project @MattyD797 and team. Looking forward to seeing your progress. What is the target price of the FinDrop?

Hi Brandon,

This is hard for me to write, because I don't have good news for you.  You can find many receivers and transmitters for 433MHz that are used for remote control, such as wireless doorbells, garage door openers, lost model locators, etc.  These are extremely cheap, a couple of dollars literally.  While this tech can be modified to operate with wildlife tags (around 150MHz), we are talking about hacking RF, not to be approached lightly.

If you really need to DIY, I see 2 options: migrate to 433MHz and build/rebuild all your kit (tags, collars, receivers, locators).  Commercial solutions are cheap and available, the work remaining is not much above handyman level.  But it is work, and not just work but also testing.

The other option is to remain with 150MHz (although you can make your own tags) and modify an aviation receiver (it lets you listen in to aircraft talking to each other or to the airport).  These receivers operate at 130MHz, which puts it in spitting range of 150MHz wildlife tags (this matters).  This is the option I'd go for, just because I know it can be done, and I have less sense than curiosity.

You mention you're working with an engineer, here are a couple of pointers:

• with an SDR (the "digital USB receivers" you mention) you can scan some bandwidth to detect radio pulses. I'm only familiar with the Lotek coded VHF transmitters but they can be received as in the Motus Sensorgnomes. I can point you at the code used there, it does involve a good amount of digital signal filtering/analysis code. One issue with the SDRs is that they're pretty power hungry so you need to plan on more solar panel and battery than you may like, e.g. even rPi Zero + SDR is probably >300mA. Another issue can be interference in that SDRs have a very wideband front-end and so TV, radio, and other stuff can desensitize the front-end.
• there are integrated receivers (ICs) that can be tuned to 150Mhz and can detect VHF transmissions, it's easy for non-coded ones, a bit more involved for coded ones. Specifically, the Semtech sx1231 or sx1276 series are widely available (often called Hope RF69 or RF96, which are modules with those chips). You need someone comfortable writing a customized driver that uses OOK mode or RSSI detection. The other issue is that while there are many suitable boards available for 433/868/915Mhz (e.g. Adafruit, Sparkfun, LilyGo, and many others) you most likely won't find one for 150Mhz. However, for RX-only the matching isn't so super important if you have a good antenna and the signal isn't crazy weak. From a power point of view these can sip power so you can run one on an 18650 for days and a small 1W-5W solar panel is most likely all you need.

Hope this helps...