Question about 3 conductor cable wiring for audio cable

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Michael Brown:
OK, I hope this doesn't sound like a stupid question, and perhaps the topic has been covered before, I don't know.  I have a 3 conductor cable that I use for my sound card interface with my radio.  I made my own cable(s) using a 3-conductor cable that I purchased from Radio Shack.  The cable has two wires contained within a braided wire.  The way I currently have the connectors soldered to the phono plugs, I am just using the two inner wires, and not using the shield.  My question is, should I re-do the soldering on the connectors and use the shield as the wire that connects to the shield of the connector, OR am I ok with the way I currently have the plugs wired?  Wouldn't the wires inside the shield be "shielded" from any RFI pickup, since the braid essentially acts as a Faraday cage, even though it not grounded to anything?  I have had no problems so far in the way I have this wired.  Any suggestions?

73,
Mike KU4UV

Bob Lewis:
The shield needs to be grounded in order to exibit any effective shielding of the inner conductors. You can leave the grounded inner conductor in place if desired, but also connect the shield to the ground connection at each end.

The two conductor with shield cable is intended for use in balanced microphone circuits where neither side of the microphone is connected to ground but the shield is grounded.

jsodus:
Quote from: AA4PB on March 19, 2013, 07:05:35 PM

..., but also connect the shield to the ground connection at each end.
I've not had any real experience in this area but I do recall reading in many places that only one side of the shield should be connected to ground so as to avoid ground-loop currents.
If it were my set-up, I'd ground just one side and try the cable; then flip the assembled-cable around the other way and see if things got better or worse.
73 Jerry KM3K

Bob Lewis:
Connecting the shield at only one end (called "telescoping shield") is only effective with a balanced circuit. With an unbalanced circuit you MUST have the common ground return path in order to complete the circuit. Telescoping shields are often used in professional audio installations when there is a problem with AC leakage currents flowing through the shields on long cable runs.

jsodus:
Quote from: AA4PB on March 20, 2013, 06:29:10 AM

With an unbalanced circuit you MUST have the common ground return path in order to complete the circuit.
Seems to me that Mike already has his circuit completed.
His next step is to only ground the shield at one end.
73 Jerry KM3K

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