1. What is the range or distance the modems can go? How far can they transmit?
This question, like many here, has a wide range of answers. There is the “text book answer”, the marketing answer and the “hey, here’s what we’ve seen answer”. We’ll try to give you a bit of all of the above, but focus on the “real world”. The modem ranges vary considerably based on environmental conditions. As anyone familiar with acoustics knows, the instrument (in this case the modem) is only one piece of the equation. There are thermoclines, absorption, snapping shrimp (funny huh, but we’ve seen stranger things) other noise in the environment…
So the question is what kind of environment do you have? Is it next to a dynamically positioned oil rig or near the beach with breaking waves? If so then you may have some issues. Distance may be limited to 1000 meters or so.
Is it a “normal” ocean environment out deep? You can see distances up to 8km. Heck we’ve even seen more than that.
Is it a bay in 10m of water? 2000m is probably a safe bet.
2. How deep can the modem go?
Really deep! Seriously, the modems have various depth ratings based on the housings. The SR-100 is rated to 12,000m. The ATM-887 is depth rated to 6000m. The ATM-885 is rated to 2000m. See above about distances because noise in the environment effects depth just as it would distance.
3. What makes up a “system”? What do I need to buy to have a complete modem?
Think of a modem system as 2 telephones, a sending unit and a receiving unit. Usually there are:
- Topside Modem
- Subsea Modem
The topside consists of a deckbox cable and dunking transducer. The subsea is a pressure housing with transducer, electronics and batteries. The subsea unit is connected to your instrument or anything you want to get data from. Yes, you can have 2 subsea units only, or you could have only 2 deck units. (See “What are the different configurations?”) The key thing to remember is that the PCB or electronics in all of the configurations are the same.
4. What frequency band should I use?
The choices are LF, MF or HF. They are 9-14kHz, 16-21kHz and 25-30kHz respectively. The most common are either the MF or the LF. Here are a few things to think about when choosing:
What other equipment in the water may interfere? Positioning systems etc. Things that may be in the same frequency band? For example you don’t want to have an HF modem transmitting at 25 to 30 kHz if your positioning system is at 27kHz. Pretty obvious, I know.
The typical theory has always been if you want to go far and deep go LF. Let’s stick with that for now. Another good reason to go LF is that you can use the LF deck box with the older Benthos acoustic releases and the new SMART modem/release combination units. Extra bonus going forward! Everyone loves interoperability.
MF is also a really good choice. The one benefit of MF that we’ve seen is that it is that nice “in-between” frequency. It is below the other pingers that may be out there and it is higher than a lot of the low frequency ship noise. It also has worked well over 6000m distances. It’s the best of both worlds.
Once you select a frequency, that frequency band goes with all of the equipment. For example if you select MF then you would order an MF deckbox, MF transducer and MF subsea unit with MF transducer.
If you don’t know – just go MF it will work!
5. How do I know if there is too much noise in the water?
This is a hard one. Most of the time there isn’t an issue. We have band pass filters on our modems that filter out noise above and below the band that we are “listening for”. Also, we have demo equipment that we are willing to give you to try it out. You may have to decrease your distance, or increase your source level setting on the modem if it is really noisy, but it should work.
6. How long will the batteries last?
That depends. How much are you going to use the modem functions? How much data are you going to transmit and how often are you going to do the transmitting?
This may be best answered with some examples. Lets say you have your subsea modem (ATM-885) connected to an RDI ADCP. You want to get current data every 20 minutes. Now lets say you have the ADCP set up to send 1000 bytes of data every 20 minutes. Your battery should last you over 6 months with certain setting in the modem. By then you’ll want to change the ADCP batteries anyway right?
7. What is the data transfer rate? (How fast are your modems?)
15360 bits/sec. Ok, that’s the marketing answer. And you’ll see other vendors claiming this or even more. But really, we all face the same challenges in the water. We, of course, feel we have some of the most robust and reliable data communication methods available. So then lets look at this a different way – what is your application and how much data do you want to transfer? Realistically if you need to transfer video at over 15,000 bits/sec you probably should run a cable. The modem is great for sampling data or getting preprocessed data from your subsea instrument. 1000 bytes every 10 minutes or so is great at a rate of 1200 bits/sec.
We have done 10,240 bits/sec in over 1000 meters of water with no errors, so it does work. But the problem is if you develop your application or plan around this and then the environment changes you may be out of luck.
Good reliable communications at 1200 or 2400 bits/sec is what I would plan for.
8. Should I consider using a modem in my application?
Yes!
9. What are the different configurations?
For the topside your choices are:
- ATM-891 – this is the standard deckbox
Or
- ATM-880 – this is the NEMA enclosure made for a buoy
Or
- ATM-885 PCB – this is our OEM board set that can be integrated
Then for either of these you need a cable and a transducer.
The cable comes in 25m increments up to 200m for the ATM-891 and 2,10 and 25M length for the ATM-880.
The transducer on the end will probably be an omni direction unit called the AT-408.
So to recap, the topside = deckbox, cable and transducer
Subsea choices are:
- ATM-885 – 2000m rated unit
- ATM-887 – 6000m rated unit
- OEM board sets for integration into you subsea bottle
There are many other options to confuse you, like having remote transducer heads and directional verses omnidirectional transducers, but we won’t go into that here. It is explained really well in the manual.
10. What’s a deck box?
We use some terms interchangeably. The deckbox is also sometimes called the topside unit or the ATM-891. Or it could be the ATM-880 if you have the version that goes on a buoy.
11. What software comes with the system?
All the software that you need to run the system is included. And right now we do not charge for upgrades. We are constantly making improvements to the software code and you can download it for free anytime if you are a customer of ours. The software consists of 2 parts: firmware and then a GUI called TelesonarPC that you load on your laptop. Your PC or laptop connects via rs-232 to the deckbox. You also can download our terminal program called Telesonar Terminal and use our AT based commands. AT commands! Can that be easier?
12. Will the modem deckbox work with my old Benthos acoustic releases like the 865-A, 866-A, 867-A or 875-A?
Yes. As of March of 2006 there is software in the modem deckbox that will allow you to range on and release the older Benthos acoustic releases.