I think you are confused a bit. You mentioned sonar which is sound but you talk about an antenna which is electromagnetic. You will need another piezo transducer to recieve the transmitted sound from the boat. One poster is correct, it will not be a simple task. Also as far as frequency, there are many frequencies used. I bought transducers from Airmar which makes the transducers for many of the commercial fish finders. I was able to choose different frequencies so that my device wouldn't interfere with the common frequencies of the fish finders and could be used simultaneously. I believe fishfinders were generally in the 100khz to 200khz range. The higher the frequency, the less range but higher resolution. If you search on google for airmar, they have very good technical info on tranmission and reception of sonar. I think it would be just what you are looking for in what you are wanting to accomplish. Good luck, FJ >From: John Nall >Reply-To: pic microcontroller discussion list >To: PICLIST@MITVMA.MIT.EDU >Subject: Re: [OT]: Underwater navigation >Date: Sat, 10 May 2003 17:33:20 -0400 > >At 12:20 PM 5/10/2003 -0700, Dave Tweed wrote: > >>John Nall wrote: >> > There would have to be a directional antenna, but since it would be >> > receive-only the length would not be critical. >> >>I don't see how "have to be directional" and "length would not be >>critical" >>go together. For pretty much any transducer, directionality is a strong >>function of size. > >I doubt we are in disagreement. I was only talking about the receiver -- >not on the transmitter end. On the receiving end we are talking about an >antenna, not a transducer. "Directional" in that turning the antenna >produces a gain or loss in received signal strength. The old-fashioned >radio directional finders (RDF's) that boats used to use before LORAN and >GPS became available used this, homing in on broadcast radio towers. I had >a Heathkit RDF on an old fishing boat that I used to have many years ago, >and the "antenna" was merely a length of ferrite (I believe) which would be >turned around to find the strongest signal. Of course, this does have >problems, because a dipole such as that has the strongest signal broadside, >but you do not know which way of the broadside is producing the signal. :-( > >I'm thinking that perhaps the problem of deciding which side of the >broadside is receiving the signal could perhaps be solved by using a >compass. Take one reading and then swim 100 yards off the end of the >antenna and take another reading. It should narrow in toward the signal >and spread out away from the signal. > >I'm not sure I agree that directionality is a function of size. Signal >strength, perhaps. But not directionality. A dipole is a dipole is a >dipole. :-) > >>Furthermore, in underwater acoustics, multipath is going to be a major >>issue that needs to be dealt with. The transmitter will need to send out >>a narrow pulse (or other signal with high time resolution, such as SS), >>and the receiver is going to have to process its input and show when the >>*earliest* input signal is the strongest, which means that it's pointed >>more or less directly at the source -- although in some circumstances, a >>reflected signal could be stronger than the direct path, distorting the >>results. > >That may indeed be a problem, although it seems intuitive that it would be >a problem which would increase with distance. That is, at a very short >distance it would not be a problem, but would increase as the distance >increases. So that is one I suppose I will just have to grapple >with. Perhaps giving the transmitter end (at the boat) a very strongly >directional signal, and rotating the transmitting antenna. > >> >Not a trivial problem at all. > >I would not think it would be trivial. I assume that the $$$ that XIOUSA >wants for their system represents their trying to recoup their >research. But for us hobbyists, a challenging real problem is far >preferable to a challenging trivial problem. :-) > >Ciao, >John > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email listserv@mitvma.mit.edu with SET PICList DIGEST in the body _________________________________________________________________ Protect your PC - get McAfee.com VirusScan Online http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963 -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body