Home Cable Asylum

Interconnects, speaker wire, power cords. Ask the Cable Guys.

[ Follow Ups ] Thread: [ Display  All  Email ] [ Cable Asylum ]
[ Alert Moderator ] [ Edit ] [ Delete ]

Re: RG's

209.215.72.171

These are numbers left over from the early days of radio, and are intended to qualify a general class of cables for a certain use.

For instance, RG-59 is suppossed to be 75 ohm, while RG-58 is 50 ohm, etc. There are other cirteria too, but they are still quite general. Within those classifications, the cables can vary wildly, with all sorts of differences in materials and actual construction.

See the repost of a note on RG cables below:

*********************
The Skinny on RG6

I have seen people recommend use of RG6 coax for simple/cheap DIY cables, usually for video use.

RG-6 is a fine cable for it's intended use, and that is long haul MATV (Cable TV) use. It can also be used with success for RF video around the house, as long as it is properly terminated with F-connectors. It may not be the best choice for home composite video signals, but it will get a picture around in the house without obvious problems.

However, for audio use, use of this cable is a different animal, and it will not do justice to the audio in most systems. Some have advocated it as adequate for subwoofer use, and others have said it can be used for the main analog signals, or for digital audio interconnects.

While each of these uses has it's specific needs, the RG-6 has the same problem for analog and digital IC use: connection of the braid to RCA plugs. Most of the commonly available RG-6 cables use aluminum braid with foil for the shield, this works OK for RF signal transmission, with a crimped aluminum F-connector on each end. But you cannot make a good connection to aluminum with RCA plugs. Even assuming that a particular RG-6 has tinned copper braid/s, the center wire is often copper covered steel, and this steel core can sound bad for analog signals, and does not help the clean transmission of digital audio signals or composite video either.

One work around has been to suggest the use of F-connector to RCA adaptors, and use RG-6 this way for subs or analog audio use. Aside from the issue of introducing yet another set of contacts and materials into the signal path, this does not eliminate the aluminum to aluminum crimp, which is not going to be very good for transmitting analog signals with high precision.

RF video signals are different than audio signals, in that they are isolated from direct signal degradation via the RF carrier. Video does not have the sheer dynamic range that audio signals have, and the levels of distortion that become visible are orders of magnitude higher than the levels of distortion that can be heard. RF signals are heavily into the skin effect region,and the signal tends to travel at the surface of the wire, rendering the steel center a moot point.

Different signals, different needs and requirements for top performance.

Some would try to defend the use of some other cheap coaxial cable for audio use, such as RG-59, or some other generic cable type.

Well, there are over 27 different specific part numbers for RG-59 coaxial cables, and the materials used for them range all over the place. Other RG numbers may or may not use good construction and materials for audio purposes.

Here are some of the materials and constructions to avoid:

Aluminum braid for the shield, explained above.

Steel core center wires, due to magnetic hysterysis from any current flow in the wire. Not even the staunchest cable nay-sayer will logically try to defend the use of steel core wires.

Foil shield, whether alone or with copper or aluminum. The foil tends to want to share the signal with the braid, or if just foil, the drain wire usually makes a trerrible ground return line. This splitting of the signal is frequency dependant, so portions of the signaal tend to travel through the braid, and other portions through the foil. Aluminized mylar is not a good conductor, nor is a nickel plated drain wire, and allowing the signal to travel through foil and braid, perhaps jumping back and forth depending on the local conditions within the coax at the foil/braid swap over frequency range, and this will not promote coherent signal transfer either.

Tinned copper center wires or braid shields. Tinned wires just don't carry the signal as cleanly as bare copper. Any sort of surface coating or contaminant will adversely affect the signal to some extent, and the HF's more than the lows, due to the skin effect action's that take place in wires/wire bundles. Note that I am not talking about dB of amplitude loss due to skin efect, but the very real and actual effect of pushing the current flow out to the wires surface.
See:
http://members.nbci.com/Jon_Risch/emf1.htm
This applies to both the center wire, and the braid shield because the so-called shield actually carries the ground return current, and has an effect on the signal just as much as the center wire does.

Solid insulation, as this maximizes the dielectric involvement of the insulation on the signal. Foamed or gas injected insulations are readily available, and will outperform the solid types.

Larger center wires, as they are prone to the skin effect causing some signal degradation. Not amplitude losses, but phase shifts and time distortions. See:
http://www.magnan.com/buffs.shtml

Remember, these are the things NOT to look for in a coax for audio use.

If you are going to build your own audio cables from raw coax, might as well get some of the best you can, this is Belden 89259. Bare copper center and braid, foamed teflon, teflon jacket, very low capacitance (17 pF per foot). May have to be special ordered, but many of the larger cable distribs have it in stock and available by the foot, you just have to cal around in your area.
Costs run around $1.20 a foot for a single coaxial cable, two needed for stereo. This may seem very high, but remember, these are the best materials for audio use, and the resulting sonic performance tends to make it well worth it for the DIYer. Even by the foot, there may be a minimum order amount, 25 feet, 50 feet. Most distribs will order the
100 foot spool (weighs 5 lbs, not so much for shipping), and this might take 4-6 weeks to get in.

The Belden website makes the local distibs info handy at:
http://bwcecom.belden.com/sales/Distloc/DISTRIBUT.htm

There are other more readily available options, although they will not have teflon insulations, they will still be a cut above the random coaxial cable choices available at RS or a local parts shop.
Belden 9259 is often available locally, and has similar construction to the 89259, just foamed PE instead of foamed teflon.

8241F is virtually identical to the 9259, but ONLY the F version.

There really are very few commercial coax's with the proper combination of optimum materials.

It turns out that coaxial is not necessarily the best geometry, but I'll leave that for the DIY notes.

Jon Risch




This post is made possible by the generous support of people like you and our sponsors:
  Parts Connexion  

Follow Ups Full Thread
Follow Ups
You can not post to an archived thread.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]