Sonar Interference

[kernr]

Good Morning -

I am starting to troubleshoot a nagging sonar striping problem on our boat. Essentially I am getting some sort of interference on our displays when in the Sonar function. We have 4 Garmin GPSMAP 1242 Touch displays and a AIRMAR B744V transducer that measures speed, temperature, and depth. I will provide photos of the striping problem displayed the transducer both inboard and outboard in this thread. Basically the problem occurs randomly often when you least want to see it and then it goes away. It almost appears that another electrical device is turning on and then about 10 minutes later it turns off and every thing goes back to normal. It does not appear to be depth dependent.

The boat is a GB Europa built in 2008 and hull #50 called Serenity. Any thoughts on how to troubleshoot this problem would be appreciated. I also have a query into Garmin for the second time to see if they have any new suggestions. I have talked with a very knowledgeable person at AIRMAR and he is adamant it is an electrical interference (EMI) with a Garmin connection or wiring. He states that the AIRMAR cable coming from the transducer to another connection is robust and not a contributor to the problem we are seeing.

Thanks for any thoughts as always,
Bob

[Hippocampus]

Have you tried ferrites around all cables and wires anywhere nearby?

[kernr]

Hippocampus -

No, not yet. I am a little bit dreading the task of trying to track where the cable actually goes. The AIRMAR person did mention ferrites and I can see they are fairly inexpensive so it is obviously an option. One of the difficulties here is it is an intermittent problem. I think I need to take a day and follow the transducer cable to determine what other cables may be nearby. Unlike some electrical problems I don't know if there is a way to use continuity checks to help in the cable tracking - possibly someone can advise is there is a method on a transducer cable.

Bob

[Larry M]

Is your depth finder dual frequency? I had a similar problem with our Simrad depth finder at the lower frequency when we were in deep water only. I never could figure it out. We also had a Furuno that didn’t have the problem.

[kernr]

Larry M -

The AIRMAR B744V transducer is dual frequency (50HZ & 200HZ). I have often switched between frequencies when striping occurs and it makes no difference - i.e. striping remains present. Depth does not seem to be a difference maker either. I feel pretty confident that it is most likely a EMI problem and I will need to find where the transducer cable goes.

Thanks,
Bob

[Mac2]

A little more history is needed. Did you own the boat when the transducer was installed? Have you always had the problem, or did it just start? I'm wondering if you added electronics that caused the problem (AIS, VHF, etc).

[Larry M]

Bob: I’ve got 10-6mm (1/4”) ferrite chokes you’re welcome to for the cost of postage.

[kernr]

Larry M -

Let me do a little more investigation and then I may take you up on your offer - Thank You!!

Bob

[Circumnavigator]

Everyone with a boat that has a wiring maze should have a wire tracer. Here's an example -- while Triplett is a good brand, I haven't used this one, so it's only an example, not necessarily recommended.
https://www.triplett.com/collections...tone-probe-kit


The transmitter puts a distinctive tone on the wire and the receiver picks it up inductively. It will work on any two or more conductor cable, but generally you want the power to be off.


Ferrites on the depth sounder cable might help, but generally it's better to have them on the cable that is the source of the problem.


Can you trace the intermittent behavior? Does it come on when you turn something on? Try with everything off and adding things one at a time.


I suppose that it could be interference from a depth sounder on another boat -- that's a guess as I've never heard of it happening -- but that would account for intermittent behavior.


Jim

[kernr]

Mac2 -

We purchased the boat in Feb 2020 right at the start of our country's COVID problems then had to get it out of FL to avoid sales tax and then in April brought her up to New England where she has been since then. So, the transducer is original 2008 equipment but the Garmin displays GPSMAP 1242 touch are probably 2015 vintage and not original - I do not know when Garmin started making them. I believe the problem has always been there just comes and goes in sort of a random fashion. but as you can imagine in doing the ICW or cruising the Bahamas we don't need to struggle seeing the bottom depth readings with this problem. i have not replaced any electronics but I have been working on pieces to get them to function correctly (e.g. getting AIS 600 to transmit own ship position and putting a NNMI into the DCS radio so it would work if needed. No real new equipment and problem has been there since 2020 - did not show up on sea trials - but did while transiting up from FL.

Bob

[kernr]

Circumnavigator (Jim) -

It usually happens when we are all alone on a transit so not another boat. Thanks for the ideas on a wire tracer - I will pick one up and could come in handy. Since the boat is on the hard for the winter and the batteries are all disconnected I will have to wait until spring time to try to find the interference culprit. Also, I don't think it is a good idea to turn on transducer while not in water (I've read that somewhere).

Right now I think I will focus on tracing the cable and where it pins out to a Display box. It could be a pin out problem. Garmin has come back with a similar thought that it could be the wrong wire adapter block being used. I believe that box might be behind the lower helm displays. Need a 50F day to check it out - Admiral says not tomorrow!! I said yes Mam!! Happy Thanksgiving!!

Bob

[diver dave]

I have done quite a bit of EMC engineering. First step is to identify the culprit. Turn off everything else and note if its self-inflicted or external. Then start to slowly bring other systems on.

“Everything else” includes engines, all dc and ac devices.

[tpbrady]

Just for grins, disconnect the connector on each end (may not be one on the transducer end) and reseat them. Many intermittent problems like that are traced to loose or bad connectors.

Tom

[sailormike]

I am now having the same issues never had them before myself. We will have to trouble shoot together.

[Ka_sea_ta]

I suspect that the issue is not interference but a bad connection in the transducer cable or a failing transducer. To verify find another compatible xducer connect it to sounder and hang it overboard. Personally I'd clean the connections first. what happens when the sensitivity or gain is turned up?

[kernr]

Good Evening -

I hope everyone got there fill of turkey yesterday - I know I did.

So, an update because I have been tallking to Garmin Support online and I got to boat today (54F in RI) before it started raining. Basically the support folks asked how the transducer cables are connected to the Garmin display. I went to boat and removed the primary display from its seat and looked behind it. There were the transducer cables going into a wire block adapter to take the 8 pin transducer cables into the 12 pin connection on the display. There is a bright yellow label on the box saying, "DO NOT USE THIS ADAPTER WITH 8 PIN DIFFERENTIAL TRANSDUCERS." Since the AIRMAR B744V is an 8 pin transducer I am waiting to hear back from Garmin support as to what they recommend prior to opening up the box to check for loose connections.

Looking at all the other wires and their closeness I am not surprised at the interference problem. The photos show the wire nests onboard behind display and coming up from engine room. The final shot is the bundle in the engine room going up to the electrical panels above. I physical traced the transducer cable into that bundle. More to come I am sure.

Bob

[kernr]

tpbrady -

Unfortunately the transducer does not have free ends that are loose at the transducer end. That's why a wire tracer is difficult to use from the transducer end. But I definitely know and see where the cable goes prior to entering Garmin display. So once Garmin support gets back to me I will take the cover off the adapter box and check out the connections. I think if the adapter box is okay and connections are tight I will have to figure out the power sources close to the transducer cable and probably use some ferrite pieces on suspected power cables.

Bob

[tpbrady]

Kernr,

I think it may have already been mentioned, but go pick up a cheap “telephone toner” on Amazon. You only need access to one end of a cable to put a tone on it, that can be heard with a handheld inductive amplifier with a probe on the end that is part of the kit. They are invaluable for finding a needle in a haystack if you can put a tone on it. Back when phones were not mobile, you could find a single wire out of 100 on a punch block pretty fast as well as trace the route of the cable that got it there from the jack.

Tom

[PNK]

Kernr,

Are you able to see your electric panel while you are looking at the sonar display? Typically AC motors create more interference than DC, so you can focus on those to begin, and see what is on or off when the interference happens, to narrow it down further, and avoid having to trace every wire on the boat.
I am not familiar with the Europa, but you probably have a number of motors that come on and off automatically, like pumps, heads, a/c, fridge, etc. Fan motors can also create such interference; there may be one or more in behind your display panel to keep the electronics cool.
Good luck, must be really annoying!
Peter

[kernr]

PNK - Peter -

You are correct - it is annoying. Sometimes (not very often) it happens when you are entering a port where you have never been before. At that point I just slow down and hope the chart is correct. Should not have to deal with it.

Normally due to better visibility around the Europa we drive from the fly bridge. The electric panels (AC panel photo below) are at the Lower Helm - of course. But when it does happen it usually stays on for a good 10 to 15 minutes - enough time to drop down to lower helm to investigate. The one item you did mention was the fan. See photo of fan right behind the Garmin display in between it and the Wire adapter block that the sonar wires come into. Certainly a potential suspect. AC motors that could be cycling while underway are the Galley fridge and the Ice Maker.

When we cruise we are minimalist regarding power usage - usually no AC required in NE, heads (vacuum) usually shut off and a tight water system so no water pump cycling.

I will check connections in adapter box first and then take a look at fan / Ac loads when power is restored to boat. It shouldn't be that hard. More to come I am sure.

Thanks for your input,
Bob