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Thread: Interference between fishfinder and chartplotter sounder

  1. #1
    Member Maast's Avatar
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    Default Interference between fishfinder and chartplotter sounder

    The new Northstar chartplotter arrived today, reading through the manual I see that it uses a 50/200 HZ sounder.

    Unfortunately my fishfinder (garmin 340C) uses the same frequencies. It seems to me that they're likely to interfere with each other, if they will I'll just disable the chartplotter as it would be redundant info anyway.

    However the plotter is twice the power output of of finder (1000W RMS vs 500W RMS)

    I want to keep the fishfinder on while I'm zipping along to see any fish schools in my path, the plotters screen will have the moving GPS and radar map displayed, along with the info from the motor (GPH, MPG, etc).

    I'd be nice to port the plotters sounder/fishfinder output to the fishfinders or a separate screen, but I dont think thats really possible..
    2696 Sea Raider Pilothouse
    "Dominion"

  2. #2
    Moderator stid2677's Avatar
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    Just thinking out loud, run one at 50hz and the other at 200hz and change as needed. I know on mine I can select either freq. Sounds like a good reason for a winter king trip, to test it out.

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    Member Maast's Avatar
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    Thats a good thought, but I lose the advantage of having a dual beam / dual frequency finder.

    Googling people who own the same chartplotter/sounder as I do it sounds like there will be enough screen real estate to have the map, sounder and fuel computer windows up at once. I'll keep the garmin as a backup then, or sell it with my 17 footer.
    2696 Sea Raider Pilothouse
    "Dominion"

  4. #4
    Member HuntKodiak's Avatar
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    If you haven't done so already, read your manuals closely for the feature I'm about to describe. The feature may be called something different, but you should have this ability to adjust none-the-less.

    I have a Garmin and a Lowrance (my chartplotter/depth combo). I normally run my Garmin for depth and Lowrance with the chart displayed. Although, I can run a split screen (chart and sonar) on the Lowrance, I prefer to have only the chart displayed on the full screen. Like you stated, I have the comfort of knowing I have another sonar available in the Lowrance should my Garmin have a problem. And, there have been times that I've displayed the sonar screen on both simultaneously.

    Now for your question, an adjustment available on the Lowrance model to alleviate interference with another depth sounder is to change the "ping speed". This alters the rate at which your depth sounder unit transmits a signal to your transducer. A higher ping rate is good for when you are driving your boat at higher speeds because you get more returns off the bottom than you would with a slower ping rate, which is good since you are covering ground more rapidly. Slower ping rates are fine for when you are moving more slowly or not at all.

    The other advantage of having this adjustment (and the one you are interested in hearing) is that you can set one of your units for a faster rate and the other for a slower rate. That should prevent them from interfering with each other if they transmit on the same frequency. The Lowrance manual specifically mentions this for owners running two sonars, and I'd guess you will find something similar in your manuals.

    Good luck!

  5. #5
    Member Maast's Avatar
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    Great info, thanks! Give that man a rep point or two!
    2696 Sea Raider Pilothouse
    "Dominion"

  6. #6
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    Default Had the same concerns

    I am in the process of installing a separate fishfinder / chartplotter for the guests to look at rather than always hovering over mine.

    I talked to Raymarine (that is the system I run) and they suggested a very similar fix to what hunt kodiak suggests. They fully agreed that trying to run both would cause problems. They even stated that having the each sounder on a different frequency may not eliminate interferance.

    One intem of note was the ability to disable the ping. This just requires a few pushes of a button and away you go.

    Now for one other idea!!
    Do you have the ability to select where your Garmin gets its depth info from? If your Garmin has a NEMA input then send the depth data to it from the Northstar. This may sound a little tricky but I assure there is no "black magic" to it! If you look at the Gamin manual it should say what NEMA sentences it outputs and recieves. So you get good depth info on the old garmin and if the Northstar acts up, you just change the depth input from the NEMA input from the Northstar to the transducer input on the Garmin.

    The other neat thing is you can have it flow the other way too. So if the Northstar transducer gets damaged you can send depth and any other data your Garmin outputs to the Northstar.

    NEMA 0183 is probably the protocal your Garmin is using. I bet your Northstar has 0183 & NEMA 2000 and perhaps another. If you are going to be getting info from your engine it must be using some way to communicate it to the Northstar.

    I wired up my engine to a seatalk network so most of my engine and fuel data could be viewed on my chartplotter. This data I was not able to send over the NEMA path.

    The only thing that may be a question is seeing schools of fish. It think you will just get a depth reading.
    Hopefully this last paragragh has not destoyed my chances at a "rep point"

    Chuck

  7. #7
    Member Maast's Avatar
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    More good info!

    From my research the Northstar is actually the better fishfinder, and the Garmin only does sonar output data - not input.

    I'm going to mount the garmin and a serarate trandsducer, but not turn it on unless the northstar goes funky.

    On the other hand the northstar m121 can output sonar data on NMEA 2000, if I can find a inexpensive external screen to interface that might be a way to go too.

    Actually I tried to do a rep point but I think only mod can do it
    2696 Sea Raider Pilothouse
    "Dominion"

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    Member Maast's Avatar
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    Default Rep points

    Somebody was kind enough to point out in a PM that to give a rep point all thats needed is to click on the scales over the post.

    I should have known that already......
    2696 Sea Raider Pilothouse
    "Dominion"

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