Soldering double shield coax

[wanders]

I purchased some Belkin 1505 double braided shielded coax to make new interconnects. Thought I would twist both shields together to connect to one end RCA jack. (As opposed to connecting only one of the shields.) Any different opinions?

 

[Speedskater]

Connect both shields at both ends. The lower the end-to-end resistance of a RCA unbalanced interconnect coax the better.

Bruno Putzeys suggested double or triple shields on coax cable well over a decade ago.

 

[wanders]

Connect both shields at both ends. The lower the end-to-end resistance of a RCA unbalanced interconnect coax the better.

Bruno Putzeys suggested double or triple shields on coax cable well over a decade ago.

Appreciate the response. I had always heard to connect to one end only.

 

[Speedskater]

Bruno Putzeys wrote:

Take a coaxial cable, take the jacket (sheath) off and dress it in a number of extra layers of shield salvaged from other cables.

But that's overdoing it.

 

[scottjoplin]

^ It'd be simpler just to go balanced and be done with it! Is the OP talking about twisted pair screened cable?

 

[kaputt]

Appreciate the response. I had always heard to connect to one end only.

When you have a coax cable and connect the shield(s) to one end only you have no current return path -> no signal flow.

The "connect to one end only" thing only works with a two conductor cable that has an extra shield around.

 

[wanders]

When you have a coax cable and connect the shield(s) to one end only you have no current return path -> no signal flow.

The "connect to one end only" thing only works with a two conductor cable that has an extra shield around.

Duh, I knew that.

 

[scottjoplin]

Aren't the shields in contact?

 

[wanders]

Aren't the shields in contact?

The wire has not been delivered yet; from the pictures, the two braided shields appear to be in contact. With other braid/foil cables I have seen, the two shields were in contact.

 

[scottjoplin]

Yes, that's what it looked like to me in the picture I found. I think if you try twisting them both together, from a practical point of view there may be too large a mass of copper to solder successfully.

 

[wanders]

Yes, that's what it looked like to me in the picture I found. I think if you try twisting them both together, from a practical point of view there may be too large a mass of copper to solder successfully.

You're probably right. If the two were separate there might be a consideration of leaving one of the four ends unattached at one end. In this case it shouldn't make any difference. Just trim off the inner at both ends; twist and attach both outters.

I started the thread because I had always used shielded twisted pair; but I'm hearing that double shield is better, and braid/braid is better than braid/foil.

 

[scottjoplin]

I think shielded twisted pair is probably better and star quad better still, but it depends on the cable length too, and then of course there's going balanced, but if we stick with unbalanced shielded twisted pair, sometimes the shield is left unterminated at one end but this is really an attempt to rectify a poor earthing scheme

 

[jcx]

triax is the term for separately insulated shields

and "the best" coax termination is 360 degrees to keep out RF EMI, not some lopsided twisted pigtail

 

[Kay Pirinha]

Yes, that's what it looked like to me in the picture I found. I think if you try twisting them both together, from a practical point of view there may be too large a mass of copper to solder successfully.

...which easily can be coped with an even greater mass of copper in the soldering tip ;-).

Best regards!

 

[scottjoplin]

Yeah, or a flame thrower

 

[AndrewT]

A wide, thin plate U shaped clamp may give a better low impedance connection onto the plane.

If the two screens are not electrically connected then use the outer screen as an interference screen and use the inner as the signal return conductor.

 

[rif]

I solder a short jumper from the twisted up shield to the rca connector. The twisted up shield is just too much of a mess for me to solder it directly to the rca. This is for female jacks. Male plugs can be different but I still have done it too, it's just less frustrating

 

[lcsaszar]

This type of cable is for crimping, not for soldering.

 

[wanders]

http://http://www.bluejeanscable.com/articles/humrejection.htm

Here's a Blue Jeans study citing Belden 1505F as a credible, unbalanced interconnect cable. Not sure if crimping to an RCA jack is feasible.

 

[AndrewT]

............. "the best" coax termination is 360 degrees to keep out RF EMI, not some lopsided twisted pigtail

The pigtail is just about OK for constant DC from which there cannot be any EMI.

The inductance of the pigtail becomes an impedance as soon as the current becomes AC (not constant DC). And becomes higher as frequncy rises.
RF interference demands good filtering and that requires low inductance. PIGTAILS are bad for EMI.