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Author Topic:   Electrical Interference To SONAR Transducer Cable
gusgus posted 11-27-2011 09:55 PM ET (US)   Profile for gusgus   Send Email to gusgus  
I am looking into moving both batteries from the splash well to within the helm. I want to move the single [unclear, perhaps means "circuit breaker"] into the helm from the splash well. And, lastly I would like to relocate the battery select switch there. My concerns are electrical interference in my transducer cable running through the trough. The other electronic cable in there along with the others is the speed wheel wire. The starter cable and all the control wires share the common path. Any advice is welcomed--in fact requested.
jimh posted 11-27-2011 10:44 PM ET (US)     Profile for jimh  Send Email to jimh     
Battery cables are not really very likely sources for interference to SONAR transducer cables. The battery represents an extremely low impedance shunt on the battery cables. About the only signal on the battery cables will be some alternator ripple, which is likely to be limited to a few volts.

A more likely source of interference to SONAR transducer cables would be the outboard engine control cable harness, particularly the KILL circuit on some engines. The KILL circuit often contains a 300-Volt signal directly from the ignition primary coil circuit. This sort of signal is many, many times more likely to interfere with SONAR than a battery cable.

domlynch posted 11-28-2011 06:56 AM ET (US)     Profile for domlynch    
Jimh, here's hopefully a similar one - I have a Montauk with 2 batteries in the console - I want to run a vhf radio antennae cable through the rigging tunnel back into the console(from a knock down rail mount on an aft rail) - wondering whether interference would be an issue here, it wouldn't suprise me if it is, my high school physics days were a long time ago... I guess it depends on the effectiveness of the insulation for all wiring + cables capable of carrying electricity (or having induced currents in them) ? I imagine when the motor is running,charging current passing in the battery supply cables in the rigging tunnel would generate electromagnetic fields around them - would this be likely to interfere with antennae cable ? I also wonder if there is some minor interference, if the squelch or noise supression on a radio can reduce this to give a more pleasant radio experience ?
Any advise/anecdotes are appreciated,
Cheers,
Dom
jimh posted 11-28-2011 08:03 AM ET (US)     Profile for jimh  Send Email to jimh     
The transmission line for your VHF Marine Band radio is a coaxial cable that is well shielded. I don't have any concern about current in the battery cable inducing interference to the VHF radio signals being carried on the coaxial transmission line. If the coaxial transmission line is in good condition and the match to the antenna is a proper one, there should be very little ingress or egress of signals to or from the radio transmission line.

Again, I would be more concerned about any high-voltage source, like the KILL circuit. That circuit tends to be noisy with spark ignition pulses.

The insulation on a wire has no effect on the magnetic field surrounding the wire. Insulation is a non-conducting material, by definition. All the cable should be insulated so that they cannot come in electrical contact with other cables.

gusgus posted 11-28-2011 08:53 PM ET (US)     Profile for gusgus  Send Email to gusgus     
quote:
Battery cables are not really very likely sources for interference to SONAR transducer cables. The battery represents an extremely low impedance shunt on the battery cables. About the only signal on the battery cables will be some alternator ripple, which is likely to be limited to a few volts.
A more likely source of interference to SONAR transducer cables would be the outboard engine control cable harness, particularly the KILL circuit on some engines. The KILL circuit often contains a 300-Volt signal directly from the ignition primary coil circuit. This sort of signal is many, many times more likely to interfere with SONAR than a battery cable.

The places the wires could run are limited. The gunnel bottom surface is an area that could be used for one or more wires, but the under floor cable channel is where all the big stuff will have to run. Would it be wise to use shielded wire for the kill circuit?

One more question is there a 2 battery wiring diagram for an '87 Outrage?

jimh posted 11-28-2011 09:34 PM ET (US)     Profile for jimh  Send Email to jimh     
I don't see much correlation between the electrical power distribution on a small boat and the brand, model, and model year of a boat. The electrical principles remain the same, no matter what the brand, model, and model year.

Keep the SONAR transducer cable separated from all other cables.

domlynch posted 11-29-2011 01:59 AM ET (US)     Profile for domlynch    
Thanks Jim.

I am thinking of 2 scenarios to "modernise" my 1988 Montauk:
(It needs (a) new sounder/GPS combo + (b) either a 27 Mhz Australian marine radio (very common here, no licence required + has ok range for me)) or VHF radio (licence required))


Case 1:

Install both of the above with all cables (ie. (a)transducer cable + (b) coax cable) in the rigging tunnel

OR


Case 2:

2. Install (a) trandsucer cable in rigging tunnel + have a hand -held waterproof & floating rechargeable VHF radio (several on the market these days)

I'm leaning towards "Case 2" - as I will purchase an EPIRB + the radio issue is much simpler/neater + these days I don't get to go out much & when I do it's usually within a few miles (say 6 - 12) of shore. (more often lesser rather than further)

Any comments appreciated,

Cheers,

Dom

jimh posted 11-29-2011 09:12 AM ET (US)     Profile for jimh  Send Email to jimh     
I do not recommend using a hand held VHF Marine Band radio as the primary radio on a boat, and particularly on a boat that goes out to sea 10 miles. If you want a more elaborate answer please start a new thread on that topic. This thread is discussing interference problems with SONAR transducer cables, a distinctly different topic.
Diver Dan posted 11-29-2011 05:48 PM ET (US)     Profile for Diver Dan  Send Email to Diver Dan     
I have had both the VHF and Loran antenna cables routed thru the tunnel and attached at the rear on both aft ss rails. Have had no interference with any cable. Haven't pulled the loran cable out--still holding out hope for a phoenix moment!
gusgus posted 11-29-2011 07:19 PM ET (US)     Profile for gusgus  Send Email to gusgus     
I am installing a Lowrance LCX111c HD unit, removing a SIMRAD Shipmate.

I have pulled so many wires from the tunnel and see there are loads of room for the few wires I will need to put there. I think that I am going to risk the trouble with the fish-finder and sonar cable and just install it.

6992WHALER posted 11-29-2011 08:16 PM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
My GPS antenna, VHF antenna, transducer cable and a couple odd electrical wires all share the tunnel with my engine harness and controls on my 17'6" hull. I have never experienced any interference.
gusgus posted 11-29-2011 09:55 PM ET (US)     Profile for gusgus  Send Email to gusgus     
Great news! Thanks!
domlynch posted 11-30-2011 05:19 AM ET (US)     Profile for domlynch    
Thanks Jimh and all others. When I get around to it, I'll run my VHF coax through the tunnel and a new transducer cable through it, too. Just need the time--Dom.
gusgus posted 12-04-2011 09:52 AM ET (US)     Profile for gusgus  Send Email to gusgus     
I read on a fishfinder blog that installing the transducer cable in the same trough as the electrical wires is OK if it is housed in a piece of PVC pipe. I would have to ask "How does that work?"
I could see if it was housed in a piece of copper (grounded) tubing it could help, but plastic pipe? The copper being grounded would protect the cable from the eddy currents.
This pvc thing just sounds like a wives tale. Maybe it is like 6992Whaler has had happen and the effort of installing the pipe was simply extra expense and work for something that wouldn't have been any trouble anyway. Maybe?
jimh posted 12-04-2011 10:10 AM ET (US)     Profile for jimh  Send Email to jimh     
PVC is non-conductive. It cannot provide any sort of electromagnetic shielding effect. It is possible to read all sorts of nonsense, particularly about matters of electrical principles, on the internet. Installing cables in a conduit, even a non-conducting conduit made of PVC, might help to keep the cables dry. The tendency for signals to interfere with one another might be less for dry cables. That is about the only basis I can see where one might say a PVC conduit was desireable to suppress interference.
gusgus posted 12-05-2011 04:52 PM ET (US)     Profile for gusgus  Send Email to gusgus     
[quote=jimh] PVC is non-conductive. It cannot provide any sort of electromagnetic shielding effect. It is possible to read all sorts of nonsense, particularly about matters of electrical principles, on the internet. Installing cables in a conduit, even a non-conducting conduit made of PVC, might help to keep the cables dry. The tendency for signals to interfere with one another might be less for dry cables. That is about the only basis I can see where one might say a PVC conduit was desireable to suppress interference.
[/quote]
I agree with your assessment. The one striking and glaring fact I have seen within his statement (PVC pipe) it that the shroud of PVC piping would keep the wire from direct shielding contact and keep the distance consistently 1/8 inch further away from offending eddy currents. It may be miniscule, however it could have been enough if the interference was minimal.

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