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Random Quote: Ignorance can be fixed, stupid is permanent.
Page 33 of the BoatUS catalog, under the heading "Installation and Maintenance Tips" says:
"Don't trim the fishfinder's transducer cable to fit your boat. If it's too long, coil it. Cutting the cable will interfere with the accuracy of the fishfinder's signal. Some manufacturers supply cable if you need a longer cable (check with our Product Information Department at 800-568-0319)."
I don't know if this really answers your question, but I bet the folks at the BoatUS 800 # could answer it pretty well. Hope this helps some.
Traveller
quote:Originally posted by leeway79: Has anyone ever cut and respliced a transducer cable with success?What is the technical reason this cannot be done?
I just installed a simrad fishfinder that has a $1200 transducer. I could not fish the cable through the tower leg with the plug on the end. They said you could cut it but you might get some interferance where it is not shielded. After I spliced it, I used some shield from another wire and soldered it over the splice. The boat goes in the water this weekend so I can try it out.
This is the same problem I am having.I have tried dish soap,grease,wd40.I have read here where you should not do this but no reason why(I understand it voids the waranty).I think if a large section of cable is cut out maybe the flow of electrons would get to the unit sooner and cause a diffrent reading.(I am not a EE terminology may be incorrect)Then it could be the shielding.Thom do you know this one.Thanks,Lee
Splicing cable is a practice routinely done by many installers. You can splice most any cable including fiber optic (glass) cable, with the correct tools. You can add length or shorten cables within MFGs listed parameters. I removed 15ft from a 30ft radar scanner cable (1/2 dia 10 conductor shielded with one coax) without and problems because did not want 15ft of cable coiled up in the box (RaytMarine Tech said not to shorten less than 12ft due to timing issues).
Step one is make sure the ducer is working properly before you start (dont want to pay for a unit that was not functional before you cut the cable).
Examine the cable: Use a raxor blade and slice a 4 cut in the outer insulation jacket, peel back the cover and see what have to deal with. The conductors should be color-coded. If its too difficult then close it up.
Joining cables: First slide one or two pieces of heat shrink over the entire cable to seal the outer insulator when finished with the splice. For each conductor, strip 1/2: from each side, slide heat shrink onto wire, push ends into opposite conductor, twist together and solder, slide heat shrink over joint and shrink.
Repeat for each conductor and stager the connections for each conductor to prevent any possibility of shorting and to keep the cable from becoming too thick. If the shield is a wrap of tin foil then wrap an extra piece of foil between joining parts the outer insulating jacket will hold in place once the final shrink wrap is used.
There are two possible reasons why manufacturers don't want you to shorten depth transducer or Radar or VHF antenna cables:
1. You might screw up the splice. There is a pretty high probability of that if you don't have a fair amount of experience splicing or putting connectors on shielded cable. (I suspect this is the big reason cutting the cable is a no-no according to most user manuals.)
2. Changing the transducer or antenna lead can change the impedence the driving device sees when the transducer or antenna is hooked up. But this is only a factor if the transducer and the device driving it are already mismatched, in which case having the lead a certain length will reduce the mismatch. If the device and its load have the same impedance the length of the cable is immaterial (except for resistive losses, which increase with length).
I can't say with authority how big a factor #2 is in depth sounder installations, but in the case of RF devices (Radar, VHF, etc.) shortening the antenna cable (within reason) should always improve system performance if the antenna and transmitter are designed right and not defective. I suspect the same holds true for depth sounders, but who knows what shenanegans the designer pulled when trying to make the lowest-cost transducer work with their unit?
Oh, by the way, the reason you want the device and its load matched is because matching assures maximum power delivery to the load and reduces stray signal which may interfere with other equipment. Stray signal can account for mysterious stuff like the fishfinder display blanking when the operator tries to transmit on VHF. In extreme cases, stray signal can even cause injury (but this is unlikely at the low power levels used on recreational boats).
[This message has been edited by Chris J (edited 05-13-2002).]
I was a professional marine electronics tech and spliced many cables that were cut by inexperienced installers(read: boat owners).
It can be done IF the integrety of the shielding is maintained, and the person has good soldering skills.
A properly tuned VHF antenna is 50 ohms, and if the cable is good, the radio sees a 50 ohm load, regardless of lenght, however, dont shorten it below 7 feet (2 wavelenghts).
the transducer cable, is a tuned circuit with the element and cable working together.
Some shortening and lenghtening can be done but within reason. For instance, if its 25 feet, I would not cut it past 15 or lenghten it past 40.
Now, if you have to cut a plug off to run the wires, Make sure that all shielded wires stay that way, not even unshielded for an inch. Does 2 bad things: 1. Screws up the impedance match. 2. can admit stray interference to the unit.
The impedance matching thing is somewhat like having a hose with water flowing thru it. If the hose is proper, the water flows smooth and with little resistance. having the shielding damaged is like a kink in the hose. Some water gets thru, but it is not right.
As said above, if you cut the depth cable, have someone who can solder handy.
My sounder came with 30' of transducer wire and there is 15' coiled up and taped. tell you something?
Captharv
I couldn't get the plug on the end of the wire for my Garmin 168 Sounder through the pipe in the hull on my 18' CC. I cut the wire and spliced it using solder and alluminum foil as a shield. The unit works perfectly. Sometimes ya gotta do what ya gotta do!
Same here. Been cutting and splicing for years. Most boats the transducer plug is too large to get through t-top supports along with radar and everything else.
Here's my 2 cents - if the transducer is a multisensor (Depth, speed, & temp) be very careful. If you just snip the cable you might blow out the Hall cell that is the speed pick-up in the transducer. The ceramic in the transducer can hold a charge (it is, afterall, just like a big fat capacitor.) A charge can develop if the ceramic experiences any thermal cycling. If the ceramic discharges while you are cutting all the conductors (shorting them all) the Hall cell can be damaged. So I guess that I would remove a section of the cable jacket and then cut the wires individually - the two wires for the ceramic can be touched together in order to discharge any voltage excesses. E Fitz.
Cutting transducer cable 
