BNC RG58 cable connections

[Slim]

Looking for some advice regarding making off some connectors. The 50 ohm co-ax cable that came with the data aerial has an outer sheath, screening mesh, inner insulation with solid conductor in the middle . All as one would expect. However, the inner insulation is coated with some kind of foil which is fused to it. Do I scrap this back a bit from the solid connector to ensure complete insulation or what? I've even resorted to u tube without success, no one mentions this foil.

😊 

 

 

 

[Alan de Enfield]

The foil is part of the electrical screening and 'covers' the holes in the braid that allow signal leakage.

 

Ideally the foil should be 'unwound' back to the level of the cut off inner insulation and then twisted in to the braid.

 

 

 

Better quality co-ax cables have a much higher density of braid (you can see above has only around 45-50%) The MOD specify a 90% coverage of braid for their radio communication cables.

 

With a high density braid you do not need to 'plug the gaps' with foil, but, it is a more expensive cable.

[Slim]

24 minutes ago, Alan de Enfield said:

The foil is part of the electrical screening and 'covers' the holes in the braid that allow signal leakage.

 

Ideally the foil should be 'unwound' back to the level of the cut off inner insulation and then twisted in to the braid.

 

 

 

Better quality co-ax cables have a much higher density of braid (you can see above has only around 45-50%) The MOD specify a 90% coverage of braid for their radio communication cables.

 

With a high density braid you do not need to 'plug the gaps' with foil, but, it is a more expensive cable.

Thanks but. In the case of my wire the foil is fused to the inner insulation and cannot be unwound in any way. I'm concerned that if I just strip back the inner insulation the foil is perilously close to the core wire especially as I can't see into or take apart the finished joint. Maybe I'll just continue scraping it back. It just seems wrong. 😕 I suspect the cable provided is cheap  and nasty as the screening braid isn't even copper.

[nicknorman]

Sounds a bit odd, but anyway the main thing is to ensure no ragged bits of foil (or screen wire) can touch the core. You can check for a dead short with an ohmmeter after assembly. If no short it will be fine as the voltages are obviously very low.

[Alan de Enfield]

1 hour ago, Slim said:

Thanks but. In the case of my wire the foil is fused to the inner insulation and cannot be unwound in any way.

 

I used to be employed as a cable designed at a cable manufacturer - we would only wrap the foil tape around the insulation as a secondary operation after the insulation had fully solidified. I know that others had the foiling wrapper incorporated at the end of the extruder, if the wrapper was set to tight and the insulation was still 'hot' than the tape could weld itself to the insulation.

 

The foil tape itself is very weak and is normally combined (stuck) with a mylar tape to give it the strength to be wrapped it will most likely be the mylar which has welded itself to the core insulation.

 

As Nick says - just scrape it back so there is a mm or two of insulation exposed (without foil) make sure there is no bits that can short out on the bare conductor and fix your connector.

[dmr]

The inner insulation is quite thick so you should be able to cut back the tape without going through the insulation. I believe that at the high frequencies involved these cables are a wave guide as much as a cable, with the energy travelling through the plastic and "steered" by the conductors, so the inner insulation has to be of the correct thickness to give the righ characteristic impedance.  This is maybe why the foil is there, otherwise the signal would escape on any tight bends 😀

[Slim]

2 hours ago, Alan de Enfield said:

 

I used to be employed as a cable designed at a cable manufacturer - we would only wrap the foil tape around the insulation as a secondary operation after the insulation had fully solidified. I know that others had the foiling wrapper incorporated at the end of the extruder, if the wrapper was set to tight and the insulation was still 'hot' than the tape could weld itself to the insulation.

 

The foil tape itself is very weak and is normally combined (stuck) with a mylar tape to give it the strength to be wrapped it will most likely be the mylar which has welded itself to the core insulation.

 

As Nick says - just scrape it back so there is a mm or two of insulation exposed (without foil) make sure there is no bits that can short out on the bare conductor and fix your connector.

Thanks Alan/Nick, was trying to use compression type connectors that didn't need a specific crimper. Gave up and ordered a crimper from Amazon that's just arrived. As suggested I'll use a blade to scratch some foil away.(nails are shot after yesterday).

[Slim]

1 hour ago, Slim said:

Thanks Alan/Nick, was trying to use compression type connectors that didn't need a specific crimper. Gave up and ordered a crimper from Amazon that's just arrived. As suggested I'll use a blade to scratch some foil away.(nails are shot after yesterday).

Quick update. Terminals made up, everything works. Thanks. 

Now, where shall I stow this never to be used 🔧