Looking for RF SHIELDING for a depth finder - trying this First


Electri-Cal
 

Just got some adhesive tape-like stuff.  It's called MWRF conductive tape, and is used to stop RF noise.  It shields the 40 - 100db, ( 10MHz - 3GHz ) wavelengths from interference.  That might help cut interference from my power cables.  The depth finder has to run beside the main cables and past the batteries, then beside the electric get home motor to the transducer.  I can get a pretty clear picture when idling, but under way it looks like snow has taken over the screen.  I turned the filter up, less resolution, and not as fish sensitive as I would like.  I imagine Bob Larkin will have a welcome observation, maybe John and others have looked at what might help clear that finder screen.

Not sure if this will work, but this tape I have here is the width that will go lengthwise and fold around the wire, at   0.6 in. wide.  A second roll is wider, and can wrap around the major power cables, after I get it fully tested for working in the water.  I figured no harm in trying, might help with any random instrument variations, even though they are 3  feet away for the most part.  Part of that power cable has to run to the helm mounted speed control, so that at least will need some protection from rfid problems too.    

All further insights welcome, ---- Cal


johnacord
 

Hi Cal,

Electrical noise issues are more frequently grounding deficiencies rather than the cabling.  Your depth sounder transducer cable should be shielded to prevent noise impression on the signal, and the shield connected to depth sounder negative of it's power supply.  If it is not than a better depth sounder would be in order for your situation.  While it can be done, it is often difficult to add shielding that is contiguous without RF gaps.

Good grounding practice is the most effective mitigation.  Single point grounding, where all the common points (ie: negative power and signal wiring) go to one point is essential:  motor controller & depth sounder controller especially connected to ONE SINGLE point only at or near the battery common.

The other practice that will reduce noise impression is keeping power wiring away from signal cabling, and have signal cables cross power cables at 90 deg.

Finally adding a noise filter in the depth sounder power cable will reduce anything coming from the power source.  These are readily available in a small package for low current devices in a case with a ground terminal connected to the single point grounding point. 
https://www.jameco.com/z/851-10-007-Qualtek-AC-Power-Line-EMI-Filter-115-250-VAC-10-Amp-RMS-Max-50-60-Hz-Flange-Mount_2230176.html

Hope this helps you.
John A


Bob Larkin
 

Hi Cal - Tell us a bit more.  What is the depth sounder powered from?  Is the motor power entirely separate? Do they share a common ground?  If so, at how many paces?  Bob


Electri-Cal
 

Thanks John A -- I will do that as time permits.  I have the rolls of supression adhesive tape, so that first, by wrapping the whole 20 ft or so on the depth finder cable, then check the signal.  If not then the spiral wrapped motor power cable as a 2 nd. bunch.  Then the grounding part you suggested looks like a good bet.  It's the main motors that do this, not the new trolling motor, so I can wait till I see what helps the most.  The odd part is that the old original depth unit is fine, just not the new multi program color unit.

Upgrades, maybe or maybe not so much, Thanks John, ----  Cal 


 

I'm no electrical expert like Bob and John, but I'm pretty sure you'll have to ground the shielding tape for it to have a chance of working.

Is th old depth sounder a Humminbird like I"ve got in Lazy Jack? Not a Cadillac of depth Sounders, but a reputable make. Is the fish fonder from Harbor Freight, or direct from China, and was it cheaper than the depth sounder? Maybe that's the problem...

On September 8, 2022 6:11:35 PM PDT, Electri-Cal wrote:
Thanks John A -- I will do that as time permits.  I have the rolls of supression adhesive tape, so that first, by wrapping the whole 20 ft or so on the depth finder cable, then check the signal.  If not then the spiral wrapped motor power cable as a 2 nd. bunch.  Then the grounding part you suggested looks like a good bet.  It's the main motors that do this, not the new trolling motor, so I can wait till I see what helps the most.  The odd part is that the old original depth unit is fine, just not the new multi program color unit.
--
John <jkohnen@...>
A facility for quotation covers the absence of original thought. (Lord Peter Wimsey)
Sent from some sort of mobile device.


Bob Larkin
 

Hi - Cal, John's assessment is that it is most likely a conducted noise problem, not a radiated noise problem.  This seems very likely. If that is the case, the tape only complicates the issue, depending on where it is grounded.

As a start, I believe it would be worthwhile to draw out a wiring diagram of everything you have, including the existing ground system and how you derive the 12 Volts from the higher voltage for the motors.  That  diagram can be valuable for future maintenance as well as showing common paths creating the noise problem. 

Good luck, Bob


Electri-Cal
 

Good Luck !!, it looks like I'll need that. and more.  Power has been out for a couple days effectively, so I have installed the RF blocking tape while I was idle.  Most everything on the transducer line has been wrapped, but testing has to wait for water to register any clutter.  Tried that yesterday, the taping has a couple open spots, which I need to remove panels and rewrap to get total coverage.  Ahhh! as a note this tape sticks like 100 mph tape, or gorilla tape, that's a one way ticket !!   UNremovable, but could have copper ground wires sandwiched between coverings as ground, that I can add after full install.

A note or two though, the depth finder is a Garmin Striker Vivid 4CV ---- Color 4 inch fishfinder, with gps, and map creating programs.  I also have the older  Eagle _ Cuda 168, a basic black/white unit still installed, and the fore floorboard mounted TV probe with screen, set in line with my helm seat. So, plenty to play with, which I ignored since the twins were out of use for quite a while.  Now maybe i'll get on that again. 
 
As per me, I didn't do a wiring chart, but the 4 strand trailer wire was used to connect everything, so I just wiggle and look to follow the connections.  All the control hookups needed to run along the sides, but I did try to get the power cords on one side only.  The battery mains run the other side, but the depth finder is on that side.  So that is now almost wrapped, for good or ill.   Water testing would help locate further problems, and I do have enough tape to wrap all power cables.  That extra part depends on what the Garmin screen shows with what I did.  If the main finder cable is secured, maybe that's enough, there is a "clutter" damper setting on the Garmin, sorta works but that restricts any chance of fish location with the other electrical noise too.  Gotta get it wet, so it works in the local water.

This will be a process I fear !!  Might be a good idea to have Surprise on dry land, so we can walk around without being in the wet stuff.  Meanwhile I will review the input, get some items to add on.  I'm not cutting and wiring in the remote speed and direction, to be added to the dash electronic controls till this clutter interference is sorted out.  I will also need some advice with this at our next lunch meeting.  As Myles Swift always reminds me, " Fight only ONE Dragon at a time  !! " ---  I repeat that daily in other situations.

I will review all the notes on this, till I get a handle on what fixes this, THANKS TO ALL ---   Cal


 









Electri-Cal
 

THread with a long tail !   Har, but here goes, from my last outing at Fern Ridge.  The wrapped depth finder tape works, I can now see the images, they are a lot clearer. The amount of "snow" on my screen is reduced by maybe 75 % minimum.  I have some but a ghost of what it was, and that's with increased details.  I had it on max noise reject, but that pretty much reduced the overall detail as well.  So, now it works, just wrap the factory cable and it works, so ok.  I also ordered some magnetic suppressor gadgets, so those I can use in addition, to the wrap.

I found some rf wrapped instrument wire in my goodie box, so shortly rewiring some of the most possible troubling instruments, adding in line fuzes, etc.  The main cables did NOT need wrapping in any way, so far as I see, and the new Newport 62 lb. motor shows zero interference, so that's good also.  I believe the problem is solved for now   The important take away is that the adhesive tape works.  Glad I did this, wish it had been done before the original install, but it does work. To make it tidy, I got some split auto wiring cover for 1/4 in, -- and overcoated the whole exposed wrapped cable for better protection of that portion, and it looks better too.