strange sonar interference

[hawkeye625]

So last season my furuno 620 unit started acting funny.  It would track riggers and mark fish fine then I'd come over a bait ball and it would fill the screen with clutter.  When that happens I loose sight of the riggers or any fish marks.  I just have clutter.  I tried adjustjing the gain, even reset to factory settings with no luck.  Anyone else have this issue or have any ideas?

 

It doesn't happen all the time, which makes me think it's not a grounding issue.

[Gill-T]

Bait from top to bottom. Last year my screen seemingly always had bait on it.

[hawkeye625]

I agree there was a ton of bait last year, but this was more than just bait.  The bottom edge of the clutter had jagged peaks if that makes any sense. 

[Chas0218]

That is the way Sonar works it picks up what whatever returns the signal first.  You won't loose the bottom because it is a strong "echo" back but might loose rigger balls or other fish lower in the water column.  Same idea is if you setup on a ledge so your traveling parallel to a shelf.  Your sonar will read the shallowest reading as your constant depth and miss everything lower of that depth.

 

So for example you are trolling parallel to a shelf at 80' and you know it bottoms out at 120'. If your sonar is reading 80' you will pick up everything from 80' and shallower leaving the 80'-120' unread.  That is why lots of guys run across a shelf shallow to deep (perpendicular) to mark fish then setup on the depth where the fish were marked.

[Guppy35]

That is the way Sonar works it picks up what whatever returns the signal first.  You won't loose the bottom because it is a strong "echo" back but might loose rigger balls or other fish lower in the water column.  Same idea is if you setup on a ledge so your traveling parallel to a shelf.  Your sonar will read the shallowest reading as your constant depth and miss everything lower of that depth.

 

So for example you are trolling parallel to a shelf at 80' and you know it bottoms out at 120'. If your sonar is reading 80' you will pick up everything from 80' and shallower leaving the 80'-120' unread.  That is why lots of guys run across a shelf shallow to deep (perpendicular) to mark fish then setup on the depth where the fish were marked.

 

That is interesting, i never knew that.  It does make sense though, now that you pointed it out.

[hawkeye625]

I've always marked bait, hooks, rigger balls and occasionally dispys but never had this issue until last year.  To be more clear, when the screen fills with clutter, it doesn't go away, it stays on the screen for 10 minutes to several hours.  Turn the unit off and on, and it comes right back as clutter.  Never thought to take a picture of the screen.

[steelydan]

NESSIE!!!!! LOL

Edited March 20, 2015 by steelydan

[Legacy]

NESSIE!!!!! LOL

Nessie???

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[Frogger]

Da da da da daaaa da da da ......... Is this where the shark bit comes in?

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[hawkeye625]

Not Nessie, but your pic might help.  The interference looks like the light blue in your pic.  If everything on your screen was red and turned upside down, it would look like mine.

Edited March 20, 2015 by hawkeye625

[final flight]

Are you running next to a boat that has a 1k transducer on the same frequency? When this happens to me on the fingers I switch to a different one

[jimski2]

The new CHIRP systems are reported to have a sharper picture and less interference from nearby boats.

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[kayaker919]

I experienced a similar issue with my Lowrance HDS on the 50kHz screen.   No other boats around.  I noticed it occurred in deeper water (>300ft) and was a wide band of clutter.  The thickness of the band and depth would vary depending on the bottom depth.   I was never able to pin down exactly what it was; it acted like a harmonic of the bottom echo rolling through the screen but it was spread pretty wide.  It looked very similar the the blue vertical lines in Legacy's post.  Adjusting gain would reduce it, but then weaken signals for fish and down-rigger.

 

I was able to eliminate it by tweaking the sonar ping rate.  (I could also make it worse by tweaking the ping rate)

 

Your issue sounds a little different, but it might be worth trying to adjust the ping rate and see what happens.

[Iceman]

Hawk:

 

Did you ever turn the unit off for 15 minutes or more right after this occurs?  If so, when you turned it back on was the trouble cleared up?  If it was, might be a heat issue on the head unit, or a ducer problem. Please let us know what you find out.

 

Good Luck:

 

John

[hawkeye625]

I'm going to try adjusting the ping, but I've had the unit for a couple of years now and never had any issues like this in the past.  I didn't turn it of for more than a few minutes so it could've been a heat issue.  I guess I'll wait to see what it does this spring.  In hind site I should've sent it back in the fall. 

[Silver Fox]

Is your sonar wire to your battery running next to anything else?

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[hawkeye625]

No, it's wired into the main fuse panel up front.  Come to think of it, my vhf wire runs beside it and it's not on all the time.  Might only happen when it's on.  I'll have to check on that.