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Old 12th December 2008, 01:16 AM   #1
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Default Steel-core Coax ??

I have a spool of what looks like useful shielded hook-up cable.
Intended for microwave freqs, it is thin coax, but with no outer jacket....the shield is exposed, but "pre-soldered" to form a 100% shield that is bendable -- in that, it will stay in the shape it is bent.
It's teflon inner dielectric won't melt, and means the stiff shield I described above, can have solder applied to it anywhere along it's length.

My question is....the solid center conductor is:
silver plated copper over a steel core.
Can the steel in the wire become a detriment to audio signals ?

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Old 12th December 2008, 02:55 AM   #2
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Many years ago I fooled around with something similar - solid tube shield, teflon dielectric, copper center conductor, meant for microwave use.

I would be surprised if the center conductor was steel. Have you confirmed this in some way? Copper is generally used for very good reasons, chiefly conductivity (high) and cost (low). Comparison of conductivity:

0.0993 106/cm ohm Iron Fe 26

0.377 10^6/cm ohm Aluminum Al 13
0.452 10^6/cm ohm Gold Au 79
0.596 10^6/cm ohm Copper Cu 29
0.630 10^6/cm ohm Silver Ag 47

( Excerpted from http://environmentalchemistry.com/yo...lectrical.html)

Maybe at microwave frequencies it is all skin effect so the signal is all in the outer silver plating, assuming it is thick enough. But given the conductivity advantage of copper vs. iron, and at microwave frequencies cost not being the primary concern, I would be surprised if the core was iron. But I have been wrong before, just ask my wife.
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Old 12th December 2008, 03:08 AM   #3
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Quote:
Can the steel in the wire become a detriment to audio signals ?
Unlikely, since microwaves tend to deal with it just fine. Small RG-174 coax also has copper clad steel for the inner conductor. Shouldn't the electrons conduct mostly on the silver anyhow?
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Old 12th December 2008, 03:38 AM   #4
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Quote:
Originally posted by mightydub
Many years ago I fooled around with something similar -
.......
I would be surprised if the center conductor was steel. Have you confirmed this in some way?
It says it on the spool. Confirmed with a magnet.

It is Belden 9307 "Conformable"

There's not much about this model # on the web, but there is info on more recent types. Similar types reveal about 30pf/ft capacitance.....not a great number, but not too bad either.

An explanation......
INFO

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Old 12th December 2008, 03:45 AM   #5
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The high-enders will turn up their noses at any steel core wire, but I'm very happy with the Belden steel core coax I use. It's lower capacitance and made for audio. IMO, short runs of what you have will be good, but buy something else for longer runs. I don't believe cables have inherent sounds, but I do believe they interact with the input and output impedances of components to produce different results. Definitely do a comparison with some other cables and report what you think you hear!
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Old 12th December 2008, 03:51 AM   #6
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And, another opinion about steel-core coax in audio...

Quote:
The use of the RG174 and RD174 in the SCPA 1 (a double shielded version of RG174) is for lower pick up noise in the unit. Consumer audio requires high impedance inputs, which are very easy to drive but also act as receiving antennas for unwanted noise.
Using a coax with good shield coverage for point to point wiring reduces unwanted pick up noise. If you think about it for a minute; what has more shield coverage, a PCB etch or a coax with better than 90% shield coverage?
The steel core of the center conductor of the wire helps ensure that the wire will not break under stress. The other reasons for the use of RG 174 is that it is a mini coax with a small O.D. and very flexible. In the world outside of audio it is commonly used as an inside the box wire, and scope probes.

There seems to be a bit of controversy on some of the cable cult forums regarding the merits of using copper clad steel. They claim copper clad steel exhibits distortion or diode rectification.
Of course we know better based on our peer reviewed and repeatable measurements of cable distortion (or lack thereof) refuting such nonsense. Its sad to see intelligent folks expend so much time on disseminating audio fallacies especially while overlooking the obvious and real impacts on fidelity of audio systems the room.
http://www.audioholics.com/reviews/p...sign-and-setup


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Old 12th December 2008, 04:07 AM   #7
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Quote:
Originally posted by Conrad Hoffman
................. I don't believe cables have inherent sounds...................,

Of course they do !!!

Everyone knows that silver cable has a clear, bell-like sound signature. Copper has a warmer glow. I would expect the steel cable to have a harder edge.
No-one makes a lead cable for the simple reason it would completely lack in high frequencies and only be usable for subwoofers.

Thats why silver solder is preferable to lead based solder. Clearer, cleaner sound.


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Old 12th December 2008, 04:37 AM   #8
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steel core coax is very common. most of the quad shield video stuff for TV & satellite is copper over steel center conductor. If you look around, you might be surprised that you have some. Just look closely at that cut end...

a) As someone pointed out this does lend it some extra strength for long runs.
b) it also saves money on copper
c) at MHz frequencies and up skin effect does take over, so all the current is in the copper (so why waste money on copper that's not even getting used - see 'b' above)

for audio purposes it may not be *ideal* - but it isn't likely to hurt.

At DC, current should flow in both copper and steel, but maybe a little more in the copper for less R... As freq rises, at some point it will gradually migrate to the copper. (look up the equations for skin effect if you care - I've forgotten, but I think there shouldn't be much diff inside the audio band...)

at audio frequencies I think a pure copper center conductor might give a little lower impedance (or at least lower DCR) - and there are other ways to acheive a good 90+ or 100% shield.

Again, not to say that the steel core is really a detriment. - hard to tell really. I personally doubt it would be audible. Many would likely dismiss it immediately...
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Old 12th December 2008, 05:09 AM   #9
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Quote:
Originally posted by redrabbit


It says it on the spool. Confirmed with a magnet.

It is Belden 9307 "Conformable"

Well I said I'd be surprised, and I am. You learn something every day, if you keep your eyes and ears and mind open. Interesting to read the explanation from Belden, I guess if I ever buy a boat again I'll worry about cable that can survive in a salt fog environment!

As I and others pointed out, at microwave frequencies it is all skin effect so the steel core is not an issue. At audio frequencies the current would flow through both the copper and steel and so there would be some frequency dependent effect due to the different conductivity, and a change in group delay. But that's all theoretical. Is it audible? Try it out and let us know! Maybe it is 99.9999% oxygen free steel, and then we can get into debates over what % of carbon content is ideal
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Old 12th December 2008, 06:23 AM   #10
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Quote:
Originally posted by mightydub
<snip>
Maybe it is 99.9999% oxygen free steel, and then we can get into debates over what % of carbon content is ideal
LOL!
I think that really could use some discussion. It's at least as useful as some other discussions I've seen around. Maybe there's an effect to be heard from the particular crystal lattice structure/grain orientation of the steel, or the steel to copper boundary...
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