Anyone know how to restore shielding to a splice?

[cjc]

Had a splice done to my PI and the perforance is not the same, with falsing wwhen the water splashes on the spliced section. Coveing it with a bicycle tube helps but it still tunes very weak. Trying a foil wrap, taped and sealed with rubber wrap next. Any ideas?
Picture shows why I need it working!
CJC

 

[Largesarge]

Best thing to do is to completely replace the cable as in all probability you've gotten water in the cable. If it's salt water the salt will cause corrosion and things will never work right. Save yourself the headache and replace it all.

 

[Eric Foster]

Hi CJC,

Splicing a coax does cause a problem, if not done with a coaxial splice. It exposes the central conductor to capacitive effects, and this is what is happening when the cable dips in and out of the sea. When using a short delay, this effect gets worse as it upsets the damping setting. At the point you are sampling, the sudden extra capacitance will give a slight change in the recovery response. Dipping the coil in the water only gives a short beep as the SAT cancels it out. You are OK if the join is always in the water - or always out of it.

You can get rid of the effect by increasing the delay to 15 - 20us, but you will lose some sensitivity to small items. I believe you can get coax splices, but I have just looked in one of my major parts catalogues and couldn't find them.

Wrapping metallic tape around the join can make matters worse, as the tape is ungrounded until it touches the water, and you can get a bigger capacitive change.

The other problem with an unshielded splice, is that it forms a small one turn TX/RX coil that is in series with the main coil. If the spice is up against a metal shaft, it will generate a signal which will vary if there is relative movement.

Eric.

 

[Mr.Bill]

First cut the bad section out, and make sure the wire is not corroded. Remove a good section of the sheathing protecting the shielded braid. Carefully roll back the shield for a few inches. Remove a little bit of the center conductor insulation, solder very close together both center conductors. Clip off excess center conductor wire, and insulate. I did forget to mention to slide a piece of heat shrink tubing on to the center wire before soldering. Use this to seal it with.

Carefully roll down the braid, it will now cover the splice. With a low heat tip, solder the braid together where you cut it. I again forgot to mention first sliding a 2 part epoxy filled, piece of heat shrink tubing over the outer cable to now slide it down, and seal in place over the finished splice.

This is only a quick explanation, but it should give you some idea. One needs to solder the shields together to maintain a good electrical connection between the cut shield braids. Without this good shield connection there

 

[cjc]

What you say is true, in or out of the water, or with added delay. My foil setup helped a bit but wish there was some kind of a replacement for the spiral soulder that is inside.
Thanks again, and good hunting.
CJC