Can you sheild wires to prevent electircal noise?

[Bustedknuckle84]

I have googled several thing and cant come up with an answer. I have electric noise at idle that shows up on my fishfinder. Is there a way to add isulation or sheilding to the wire to help prevent electrical noise?

 

[j_martin]

Re: Can you sheild wires to prevent electircal noise?

Add a noise filter to the power line at the fish finder.

If that doesn't work, resistor plugs in the engine.

Check all your grounds. Route the ground for the fish finder back to the battery, or a main distribution buss, not to the control ground shared by the engine and instruments.

hope it helps
John

 

[Bustedknuckle84]

Re: Can you sheild wires to prevent electircal noise?

help alot! thanks buddy!

 

[jhebert]

Re: Can you sheild wires to prevent electircal noise?

I have electric noise at idle that shows up on my fishfinder.

Your situation is unusual in my experience. Usually the interference shows up when engine speed increases. At idle speeds the interference is usually not as noticeable.

Typically the source of the interference is from ignition spark. You should observe that the pattern of interference changes as the engine speed changes. Also, I assume you already have installed radio-frequency suppressor spark plugs. Check your engine manual for the recommended optional radio-frequency noise suppressor spark plugs and install them, if you don't have them already.

To provide more immunity from interference, try to keep the cable connecting the transducer and the echo sound as far away from the engine wiring harness as possible. Certainly do not bundle them together.

To see if the interference is due to common mode noise in the electrical distribution, bring a second battery aboard the boat and temporarily operate the echo sounder from the second battery so that it is completely isolated from the battery running the engine. If this reduces interference, then you can benefit by installation of power line filters on the power wiring for the echo sounder, and you should try running the echo sounder power directly to the battery terminals; this will also reduce common mode noise in the power.

 

[Midnight Krawler]

Re: Can you sheild wires to prevent electircal noise?

There is two types of noise interference. Low frequency and radio frequency.
Low frequency noise requires an inline filter.
http://www.tss-radio.com/products/pie-5-amp-in-line-power-lead-noise-filter

For radio frequency a ferrite choke on the power wire will work. (http://www.radioshack.com/product/index.jsp?productId=3012599)

Use a combination of these on all electronic devices and eliminate your noise problem.

 

[ChampionShip]

Re: Can you sheild wires to prevent electircal noise?

Try wrapping wires with tin foil till you find which one is making the headache. It's typicaly advisable to not install a sonar on the same battery running the engine for this very reason.

 

[sschefer]

Re: Can you sheild wires to prevent electircal noise?

Batteries do not cause RFI. It makes no difference which battery you use. The noise you're seeing is Radio Frequency Interference and can be caused by any number of onboard objects. Most common is spark plug wires which can be replaced with RFI sheilded wires. You also want to look for loose deck fittings, chains, anchors, etc that are vibrating against themselves or something else. Corrosion will also cause an increase in RFI so if you have corroded battery terminals or cables or deck fittings that are loose and corroded clean them up. Dirty motor brushes or a scored commutator in a motor is often a culprit. .

Ferrite chokes will help and STP wire (shielded twisted pair) bonded to ground on one end will also help. The level of interference is based upon the order of the harmonic present. Odd orders are canceling and even orders are amplifying. Change the order to anything below 9th order and keep it odd and your problem will seem to go away.

 

[bruceb58]

Re: Can you sheild wires to prevent electircal noise?

The level of interference is based upon the order of the harmonic present. Odd orders are canceling and even orders are amplifying. Change the order to anything below 9th order and keep it odd and your problem will seem to go away.

This is nonsense!

Curious, why are you talking about harmonics in this particular situation? And LOL...what in the heck are you trying to tell a person to keep harmoics under 9? You even know what causes harmonics and why that doesn't even apply here?

 

[bruceb58]

Re: Can you sheild wires to prevent electircal noise?

Move the fishfinder to a battery that only has the fishfinder on it as a test. If that causes the noise to go away, your source of noise is in the wiring. I prefer to run twisted pair power wiring to a battery rather than source the power at the fuse block at the dash.

An easy way to make a twisted wire pair is to chuck two wires in an electric drill and have a helper hold the other ends while you operate the drill.

Run your transducer cable away from all power lines if possible to prevent noise being induced onto that cable.

 

[sschefer]

Re: Can you sheild wires to prevent electircal noise?

This is nonsense!

Curious, why are you talking about harmonics in this particular situation? And LOL...what in the heck are you trying to tell a person to keep harmoics under 9? You even know what causes harmonics and why that doesn't even apply here?

Yes, I know what causes it, pretty much explained that. You must be thinking of a harmonica and in that case you are correct, it would not apply here.

 

[bruceb58]

Re: Can you sheild wires to prevent electircal noise?

Yes, I know what causes it

Then explain how harmonics even matter here then? Please fill us in how you would attempt to control them. You are suggesting the OP to control something yet you don't give him any examples! Can't wait to hear this!

 

[reddogg]

Re: Can you sheild wires to prevent electircal noise?

I used to use some stuff called mu-metal to shield car audio wires when I was into it, that would help though I don't know how it would hold up in a water environment.

red

 

[sschefer]

Re: Can you sheild wires to prevent electircal noise?

Then explain how harmonics even matter here then? Please fill us in how you would attempt to control them. You are suggesting the OP to control something yet you don't give him any examples! Can't wait to hear this!

EMI affects the performance of electronic equipment in a marine environment. Noise cancellation or amplification can be measuered in harmonics. From that you can determine if those harmonics will interfere with the frequencies that the equipment is designed to be operated at.

For instance, if your transducer is operating at 200Khz and something else on your boat is also producting a 200khz frequency or an even order harmonic then it's highly likely that you will see that as noise or interference. Odd order harmonics are often desireable but beyond the 9th order they do tend to be less controlled and therefore are best eliminated.

You need a sensitve reciever and an O-scope to pinpoint the exact frequencies being generated by your boat. I have that equipment and have surveyed my boat. Tightening loose bolts, removing corrosion and relocating stored items will often improve the situation. I've even seen rods stored with their tips against the hull cause interference.

 

[bruceb58]

Re: Can you sheild wires to prevent electircal noise?

First of all, you can't use an oscilloscope to determine what the frquencies are present. You need a spectrum analyzer. An O-scope only measures voltages in the time domain. For example, if you had something generating a pure 100 Khz sine wave and there was a 2nd order harmonic of 240Khz that was 20dB down, not only would you not see it with an O-scope, but a 20dB harmonic at 200Khz would have such low power it would unlikely cause any interference with a fish finder. With an O-scope, once you have a mixture of frequencies, its almost impossible to determine the actual frequencies of all the components of the signal. It might help with determing a noise floor but using it to actually determine actual frequencies is pretty much useless.

I am a EE and my main design career has been with digital signal processing where I deal with harmonics and noise levels(SNR). What you are writing here is just plain wrong.

So here is a picture of what a sine wave with multiple harmonics of various phase would like on an O-Scope. Please tell me how you determine what harmonics are present here in this picture. The answer is that you can't.

 

[TerryMSU]

Re: Can you sheild wires to prevent electircal noise?

Thank you Bruce. As another EE I was just trying to decide whether to comment or not. As far as the ninth harmonic, the average boater has no control over which harmonics show up. In addition, the even vs. odd harmonic issue is totally bogus. Also, noise rejection is measured in decibels, NOT harmonics.

As far as mumetal, mumetal is ferrous and does a great job of shielding magnetic fields. Because it is ferrous, it will probably rust like crazy. If I were shielding the power wires, I would use shielded twisted pair, but shield twisted pair cable is not easily available in large wire sizes. The other thing I would od is ground the offending source. In this case, the offending source is likely his trolling motor. Ground the case for the motor portion of the troller and watch what happens. The noise should drop markedly. Also, use what is called a common mode choke. This is the coil that HB is trying to get folks to use in the first place.

Frankly, based on my experience, HB is doing all the right things technically to fix this problem. Dealing with an electromagnetic interference problem like this one is a real challenge. It takes both fixing the noise source and fixing the device that is responding to the noise. Following the advice that they give you will ultimately have a very good chance of fixing the problem.

TerryMSU

 

[dingbat]

Re: Can you sheild wires to prevent electircal noise?

As far as mumetal, mumetal is ferrous and does a great job of shielding magnetic fields. Because it is ferrous, it will probably rust like crazy.

Mumetal doesn't rust. 80+% nickel, ~15% FE, ~5% MO. THe balance is SI, MN and a couple of trace elements

 

[sschefer]

Re: Can you sheild wires to prevent electircal noise?

First of all, you can't use an oscilloscope to determine what the frquencies are present

.

While a specany is a nice piece of equipment it is nothing more than a fancy radio receiver and an oscope. As for TerryMSU, you are correct to a point. The average boat owner can do a lot to control the spurious frequencies that show up. Consider that a graphite fishing rod is really a nice antenna and that tip rubbing against the hull is a pretty good transmitter.

Some good advice was given pertaining to ignition systems, choke coils and Mumetal to help keep the noise from bothering the equipment. My point was that if you take the time to look around you can usually find the source. In small boats it's pretty easy. I did it on US Navy Ships throughout my career.

 

[bruceb58]

Re: Can you sheild wires to prevent electircal noise?

.

While a specany is a nice piece of equipment it is nothing more than a fancy radio receiver and an oscope.

Which is like saying a truck and a shopping cart are the same because they both have 4 wheels.

 

[kahuna123]

Re: Can you sheild wires to prevent electircal noise?

Make sure you have a good ground at the dash buss where the grounds tie in with the fish finder. I had a customer that lost this and the 200khz through hull started becoming a conductor. It did show up on his color scope fish finder as interference. by the time he brought it in it cost him $2,000 for a new shaft. this was a 25ft inboard diesel that was dry docked when not in use. It only took a few day trips to eat through it.

 

[Bustedknuckle84]

Re: Can you sheild wires to prevent electircal noise?

Your situation is unusual in my experience. Usually the interference shows up when engine speed increases. At idle speeds the interference is usually not as noticeable.
.

Thats what i cant figure out, with motor off the display works pretty good with radio and and stereo on.

UPDATE:
So far mounting ground to steering rack didnt work as i was advised after i did it, also clamp on suppressor made no difference.

will this help anyone, seems like it has to be voltage related, as in when i have more juice from the battery i get less interference.

ex: when first getting on water and first starting motor up(idling) i get horrible lines on display . After driving(batteries are charging) when i get to my location to fish i cruise (idling) and not much interference shown on display.