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Discussion Starter #1
i'm looking at the lowrance 520c or the 527 df igps.the only diference i see is that one has the internal gps antenna,for 50$ more . my question would be, will the internal antenna work as well or better than the external antenna? or would i be paying 50$ just to not see the little round antenna?would one have better reception in heavy fog?i noticed they don't list the 32 c anymore is this unit replacing the 32c?
thanks
rich
 

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I asked the Lowrance expert Darrell Rollins specifically the same question. Darrell's advice was stay with the external antenna unit 520c. I planned to mount this unit for front trolling motor use. You need to have the GPS antenna as close to where your sonar transducer is mounted to pin point where the coordinates are in relation to the sonar signal. For example if you sonar/GPS unit is 5 feet away from the transducer, you have a 5 foot error in regards to the GPS way points or sonar image displayed. The built in antenna units still have a few bugs compared to the external units. I'm sure Jim will have clearly stated explanation.
Tom
 

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As long as the external antenna has a clear view of the sky, even to the horizon for low satellites, it will give highly accurate positions. Some folks have mounted it under the boat deck, thugh that isn't recommended. Any metal, metallic paint, wood, etc will block signals. There's no way you could use low-horizon satellites, your best ones up there, far better that those overhead.

The internal antenna is much less forgiving. The head unit can't be flush mounted, in fact must be positioned with top straight up. If you had to tilt it back to view it, chances are you couldn't get a position. They won't do on a bow deck since that requires the screen aiming up at you.

The 520C replaces the 332C.

Tom already indicated the best way to match antenna and transducer. If when setting a waypoint you take action with the pop up window you see after pressing WPT, you can get accuracy to within 5' for whatever sonar view you have (like a brush pile) assuming antenna is over the transducer. Choose point averaging and let the unit collect 30 second's worth before creating the waypoint. I let it go longer if the boat is still, taking time to assign a peculiar name that describes the spot. if you end up with a long list of default names like Wpt 001, Wpt 002, etc, they lose value later when you have no recall of what was there or why you made it. "Brush Pile" would be a better name. "Laydown". "Ridge". "Ledge". There are many ways to organize your data. I'm going to write an article on it.

Jim
 

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Discussion Starter #5
if i mount the antenna on the bow of the boat right next to the trolling motor mount will this give any interferance?
I can't wait for your article between you and tom i have sooooo much to absorb.
thank you both
rich
 

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An antenna close to the trolling motor head doesn't normally get interference from there. Hooking your sonar to the same power supply as the trolling motor is on can. The motor in the water is what causes problems. When they wear out (motor brushes) they begin to get electrically noisy then later make noises you can hear and feel.

Jim
 

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The one thing that I forgot to mention is the consul units usually have their transducers in the very back of the boat on or just inside the transom and is already about 6 feet from the antenna. The boat is moving forward away from the sonar signal creating more distance from the target by the time you see it as a returned image on the sonar units screen. If you hit instant way point you maybe 25 feet or more away from the planned target. You need to factor that in when trying to establish accurate readings by going back over the target and splitting the distance in half. If you have a trolling motor unit with the antenna located over it, then the target is below the sonar signal and a accurate way point is achieved.
Tom
 

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Discussion Starter #8
when i get it it will go on the bow next to the trolling motor bracket and the transducer on the trolling motor,the garmin that is in the front now will be moved to the steering area.unless momma lets me get 2 of the lowrances.then of course the garmin will have to go to a new/used john boat for the rseivoirs.
thanks again for your help i'm sure there will be more questions once i get it and install it.
rich
 
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