I was wondering about what would happen, if one decided to use a coaxial cable in "reverse" mode - that is, using the shield as the signal (hot) conductor, and the center conductor as the return (ground).
Of course, I am discussing this in terms of shielding. Would it lose its whole shielding capability?
I feel that electrical shielding would be compromised, since the outer conductor would not function as a "Faraday cage" - as it does when the shield is grounded. And that shielding against current-field noise pickup would be roughly the same, since the geometry doesn't change a lot..
Of course, my assumptions could be complete nonsense. 😛
Of course, I am discussing this in terms of shielding. Would it lose its whole shielding capability?
I feel that electrical shielding would be compromised, since the outer conductor would not function as a "Faraday cage" - as it does when the shield is grounded. And that shielding against current-field noise pickup would be roughly the same, since the geometry doesn't change a lot..
Of course, my assumptions could be complete nonsense. 😛
good question.
I don't know.
In one respect the two operate the same. They both maintain close coupling of the Flow and Return signal.
I think you are right about the screen signal being exposed to interference.
I don't know.
In one respect the two operate the same. They both maintain close coupling of the Flow and Return signal.
I think you are right about the screen signal being exposed to interference.
You would get almost no electric field shielding, but the same magnetic 'shielding' due to concentricity.
I will let others argue about whether the shield acts as a Faraday cage, as there seems to be some difference of view on exactly what this term means.
I will let others argue about whether the shield acts as a Faraday cage, as there seems to be some difference of view on exactly what this term means.
At audio frequencies the core is ground, so the shield is simply a conductor with a fairly high capacitance to ground. It will be capacitance coupled to any nearby signals
Thank you all for your neat answers!
DF96, you are quite right to ask this. It has ended up as an exercise in coax operation (and physics, of course!) but it started out as a "guitar gadget" problem.
I was wondering what cable to use to supply DC power to some effects. I started considering the coaxial solution, when I encountered the following problem:
Nearly all guitar pedals use a sleeve hot, tip ground configuration for wiring the DC plugs. That is to take advantage of DC jacks with a switch, so they can switch off the inside battery when external power is applied.
Now, if I was to preserve this configuration for my DC plugs wiring (which I have to), using coaxial cable would mean that I had to solder the shield foil to the tip terminal of the plug, and the inner conductor to the sleeve terminal of the plug. This way, the coaxial would work as a coaxial, not in the "reverse" mode that we examined.
But, needless to say, this soldering setup would be unreliable compared to the normal wiring of the coaxial, where you solder the foil to the sleeve and the inner conductor to the tip terminal. It would at least require more delicate handling and possibly some heat-shrink tubing to ensure that the exposed foil shield could not touch the sleeve terminal.
Not to mention the fact that the cable is attached to the sleeve on the entry, where a metal "hook" on the sleeve "grabs" the cable stable. That means even less room for working the heat-shrink solution.
To cut the story short, I wondered what the effect of soldering it the normal way would be. Thus the opening of this educational thread. 🙂
Pardon me for the long post!
DF96, you are quite right to ask this. It has ended up as an exercise in coax operation (and physics, of course!) but it started out as a "guitar gadget" problem.
I was wondering what cable to use to supply DC power to some effects. I started considering the coaxial solution, when I encountered the following problem:
Nearly all guitar pedals use a sleeve hot, tip ground configuration for wiring the DC plugs. That is to take advantage of DC jacks with a switch, so they can switch off the inside battery when external power is applied.
Now, if I was to preserve this configuration for my DC plugs wiring (which I have to), using coaxial cable would mean that I had to solder the shield foil to the tip terminal of the plug, and the inner conductor to the sleeve terminal of the plug. This way, the coaxial would work as a coaxial, not in the "reverse" mode that we examined.
But, needless to say, this soldering setup would be unreliable compared to the normal wiring of the coaxial, where you solder the foil to the sleeve and the inner conductor to the tip terminal. It would at least require more delicate handling and possibly some heat-shrink tubing to ensure that the exposed foil shield could not touch the sleeve terminal.
Not to mention the fact that the cable is attached to the sleeve on the entry, where a metal "hook" on the sleeve "grabs" the cable stable. That means even less room for working the heat-shrink solution.
To cut the story short, I wondered what the effect of soldering it the normal way would be. Thus the opening of this educational thread. 🙂
Pardon me for the long post!
Coax is made as a shielded cable. If you use it to carry a DC power supply, it is now configured as "wires". DC supply wires don't radiate anything nor do they pick anything up. You can use coax from a power supply, but you can also just use two wires. LOTS of power adpators has plain old zip-pair wires.
I am well aware of the reduced need for shielded DC cables (although I believe that even RF trash is of no value to be picked up), but the zip cord solution is not of my taste. 😛 I know that this is not a scientific remark!
Enzo, why do you state that DC cables can't pick anything up? I realise they emit only DC fields in practice (so "nothing"), but why would you propose that they are not vulnerable to interference?
Enzo, why do you state that DC cables can't pick anything up? I realise they emit only DC fields in practice (so "nothing"), but why would you propose that they are not vulnerable to interference?
Yes, any piece of wire can act as an antenna, but think about it. How many amplifiers distribute power throughout with shielded cables? On supply lines, we do have decoupling caps, but those are to squash interference from the circuit itself, not the outside world. generally the low impedance of the power supply doesn't allow much picked up to go anywhere.
Your concern was power supply wires from a power adaptor. I suppose some internal control line running on DC could be more sensitive, but that isn't what we have here.
Your concern was power supply wires from a power adaptor. I suppose some internal control line running on DC could be more sensitive, but that isn't what we have here.
Enzo, thanks for your answer. But based on your comment is seemed like you proposed that DC cables can't pick anything up in general, like physic's laws make them invulnerable. That's why I asked.
I agree on the reduced need for DC power shielding compared to other signal wires, it is just another thing. 🙂
The shield is only 70-90 % coverage anyway. Bedfoil is really not good either.
The published skin depth equations(physics texts) are incorrect at any frequency, that statement usually starts a religious war but its true.
So, use ferrous iron tubing if a good shield is the goal.
Inverted as you described is a basic antenna but would be an interesting subject for tests as there would be an internal parrallel ground plane. It would be resonant at some frequency.
Try coax with active shield if you have the power budget.
cheers
The published skin depth equations(physics texts) are incorrect at any frequency, that statement usually starts a religious war but its true.
So, use ferrous iron tubing if a good shield is the goal.
Inverted as you described is a basic antenna but would be an interesting subject for tests as there would be an internal parrallel ground plane. It would be resonant at some frequency.
Try coax with active shield if you have the power budget.
cheers
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