my transducers coax is cut can it be spliced back

Discussion in 'OnBoard Electronics & Controls' started by the brain, Jan 28, 2017.

  1. the brain
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    the brain Senior Member

    my transducers coax is cut can it be spliced back the cut part will not be exposed to direct water (it will be inside the transom)

    the temp sensor is also cut same ? for sensor

    Thanks STB
     

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  2. gonzo
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    gonzo Senior Member

    It is OK to splice the wire. I usually solder them. The shield should also be soldered and preferably make sure there are no gaps. If there are gaps, some noise will be introduced in the signal.
     
  3. kinggeordie
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    kinggeordie New Member

    i would heat shrink the joints the also pot the joint with a small piece of tube filled with hot melt glue or epoxy
     
  4. PAR
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    PAR Yacht Designer/Builder

    I also solder the conductor, though the RF shielding just needs to overlap to be effective as a shielding, I also solder it too. Shrink tube it and if any gaps in the shielding was visible during the repair, wrap the area with some tin foil before shrink tubing it.
     
  5. tom28571
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    tom28571 Senior Member

    Regular heat shrink tubing will not be waterproof but you can get tubing with a sealant/adhesive inside that will waterproof the splice after heating.
     
  6. PAR
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    PAR Yacht Designer/Builder

    Good point and one I've taken for granted, as I only use epoxy lined tubing.
     
  7. Scot McPherson
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    Scot McPherson Senior Member

    Well the shielding in coax is a conductor as well as a shield...Old fashioned RF cables were what was called Ladder Line, or two wires carefully spaced to assure a fixed and even impedance. Although a connector will attenuate the signal a little, it will help assure the impedance is matched at the joint. If there is an impedance mismatch, you lose more than just signal attenuation, some of the signal is reflected back the way it came (this is called a standing wave, and is measured as a ratio..SWR Standing Wave Ratio). You want this SWR to be as close to 1:1 as possible to avoid signal reflection at the joint. In low level applications, this isn't usually harmful to the electronics as it is in communications equipment, but it does represent even more signal lost along the feed line.

    Simply overlapping the shielding will increase the mismatch of the impedance at the joint. Remember it's carefully spaced, and carefully manufactured so the shielding is perfectly distributed around the dielectric core. Do yourself a favor and spend the couple bucks on a compression connector, test it, then shrink wrap it to keep moisture out of the line.
     
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  8. the brain
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    the brain Senior Member


  9. Sparky568
    Joined: Jan 2017
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    Sparky568 Junior Member

    Scot is right on point. Back in the late 80's early 90's I did hundreds of 75 ohm BNC connections for the now defunct DEC Ethernet networks. I did a lot of work for Bayer in their main plant and every cable run would need to be tested with an MTDR. When starting out in the networking field I did some tests with kinked, damaged and the splice fix. The return signal was quite obvious. The connector coupling is the best way.

    Here's an Amazon link.


    https://www.amazon.com/Coupler-Fema...F8&qid=1487903891&sr=8-6&keywords=bnc coupler
     
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