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  #1  
Old 08-10-2007
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GPS Sonar vs. Depth Finder: Interference?

Bought a Garmin 498 GPS/chartplotter/sonar, with in-hull transducer. The transducer is an Airmar P79. Little did I know, at the time, that the PO of my boat had upgraded the depth sounder to a Raymarine unit, including, you guessed it, an Airmar P79 transducer. Naturally he installed the depth sounder's transducer right where the instructions said to. (Or as close as possible, given access restrictions.) Now I'll be doing the same, and installing the sonar's transducer directly on the other side of the keel--or so close as the difference makes no nevermind. The Raymarine depth sounder is appearantly running its transducer at 200KHz. Unless there's some magic involved here, I imagine I won't be able to run the sonar at 200KHz, otherwise they'll interfere with one another and neither will give readings worth spit. So it would appear I'll have to run the Garmin sonar at 50Hz, right? Will I get any kind of worthwhile picture of the bottom that way? I'll be in shallow, sometimes very shallow, water.

TIA,
Jim
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Old 08-10-2007
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Hello,

My boat came with basic instruments - knot / log, wind, and depth finder.

I added a Lowrance GPS / SONAR unit. The transducer is a dual frequency unit 50 and 200 khz. When I installed it and turned it on it worked great. Then I noticed the original depth finder would blink. I figured the two transducers were interfering with each other. On the Lowrance unit I changed the SONAR from 200 khz to 50 khz. Now both units are happy. I can still see plenty of detail on the bottom. You might lose detail in deep water, but I don't think that is very important.

Barry
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Old 08-11-2007
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I think you'll be fine in shallow water with it at 50 khz. I think you'll lose resolution running it at 50 Khz though. IIRC, the higher the frequency, the better and finer the discrimination of the sonar image. If you aren't using it for a fish finder, it shouldn't really matter all that much, but if you want to use it as a fish finder, I think running it at 50 KHz will lose you a lot of fish.
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Thanks for the info, guys.

Nah, SD, I find my fish at Mickey D's . Mmmm... Nothing like a well-prepared particle fish!

Jim
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There is also the option of splitting the transducer that is already installed to work for both units. Most manufacturers sell the coupler that will allow you to use the same transducer for two depth finders. I prevents the option of redundancy, but would make install / use much easier.
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Old 08-12-2007
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Originally Posted by T34C View Post
There is also the option of splitting the transducer that is already installed to work for both units. Most manufacturers sell the coupler that will allow you to use the same transducer for two depth finders. I prevents the option of redundancy, but would make install / use much easier.
Thanks for the idea. I checked Airmar's web site and Google'd for it, but there doesn't seem to be such a beast for those transducers.

Jim
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Old 08-12-2007
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I think there is a piece of equipment out there called "Pas-Thru Box" that will allow you to link a bunch of different electronics together. You may be able to use one of these to wire the old and new together. It's nothing more than a water tight terminal junction box. It looks slick, and might work for you.

http://www.westmarine.com/webapp/wcs...&classNum=null
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