Difference Between Spiral and Mesh Braiding in Cables?

[Rommel]

I would like to determine the differences between spiral and mesh braiding when it relates to the coax cable - HDTV and Audio uses.
Specifically, in the HDTV component cables, sold through-out the market. I would like to determine the charcteristic impedance of the spiral braiding cable - can it be used as an HDTV component cable and, if the impedance is other than 75 ohms, will it have any significant impact on the actual analog signal itself to the display?
Also, does the foil lining, whether it is present or not in the cable, effect the RF noise reduction, if spiral braiding is used?
Can anyone point me to sites which give detailed explanations to my questions?

-Rommel

 

[gene]

Rommel;

It's funny that you are inquiring about spiral shield cables since I am authoring a very detailed article about them and will publish it soon. Bottom line is spiral shields by themselves are not very effective and many companies use them because they are cheap cables to produce and easy to terminate. I don't recommend these type of cables for video applications unless they have additional foil and braided shielding.

 

[Rommel]

Thank-you! When? And may I have the first copy?

Gene:

I am very anxious to read your paper. When will it be published?
Away from the subject - are you and Steve Della Sala related?
This website is very informative and I am very impressed with its' knowledge base. You guys do excellent work!
Can you give me a little more in-dept detail as to why you do not recommend the "spiral?" If used, considering the cost as the importance, will the signal be significantly affected and what major impact, if any, will it do to the video signal?
Again, thank-you very much for your info - I look very much to reading the article you are writing.

Sincerely,

-Rommel

 

[gene]

Away from the subject - are you and Steve Della Sala related?

Though I don't always like to admit this, Steve is my brother Thanks for the compliments.



Ok here is a quick take:

The shielding effectiveness of a coaxial cable can be expressed in terms of the shield transfer impedance. The lower the transfer impedance the more effective the shielding. This means that the signal stays on the inside of the cable and any noise present remains on the outside of the cable, and never the twain shall meet.

At low frequency the transfer impedance is equal to the dc resistance of the cable. As frequency increases the transfer impedance of a solid homogenous cable shield decreases due to skin effect and the shielding of the cable increases. Skin effect causes the noise currents to remain on the outside surface of the shield and the signal currents to remain on the inside surface of the cable.

For a spiral shield cable the transfer impedance contains two terms, one due to the longitudinal component of the shield current that decreases with frequency, and the other due to the circular component of the shield current that increases with frequency. The net effect is that the transfer impedance increases with frequency above about 1 MHz. The high frequency transfer impedance is a strong function of the pitch angle, the larger this angle the larger will be the transfer impedance and the less shielding effectiveness the cable will have.

This is from an excerpt from an article I am working on with Industry EMC Expert Henry Ott.

 

[Rommel]

Interesting...

Gene,

I hope I'm not being a pest - this brings me to my next question. I want to save money, but on the other hand, I want to make sure I do not go overboard or do an "over-kill" - if I have a choice between selecting varying braids of cables. I realize the effects of RFI and EMI - but I just live in a room with my HDTV and set top. I don't have any other gadgets (my girlfriend does; but she doesn't use them while I'm around). I hope you can help me decide.
Many manufactures are selling these flavors: 25, 45, and 95% braids. Do you have any practical science or data to support why the Mfr's are getting away with selling the 25 and 45, and not consistently sticking to 95% briad (aside from the cost of the manufacturing process)? Could they get away without braids - maybe 0%?
I am very confused.
Oh, and one other thing. Your statement:
"The shielding effectiveness of a coaxial cable can be expressed in terms of the shield transfer impedance. The lower the transfer impedance the more effective the shielding. This means that the signal stays on the inside of the cable and any noise present remains on the outside of the cable, and never the twain shall meet."
Is transfer impedance measured in Ohms? Can you give me more explanation - I'm lost? The rest of the paragraph made me even more confused - sorry.
As alway,

THANK-YOU!

-Rommel

 

[gene]

Rommel;

I posted the article about Spiral Shields.

As you can see by this article Spiral Shields are not a good idea for video cables. By themselves, they offer very little protection. A good video cable should have a combo of braid and foil or at a few braided shield layers.

 

[Rommel]

DC Loop Resistance of Spiral?

I have noticed (I think not mention in the articles), which leads me to the next question - will the total DC resistance (loop resistance) increase in a spiral braiding? If it does, will this have an effect on Luma and the color differences - essentially reducing the component signal level - considering no AGC?

-Rommel

 

[jneutron]

- will the total DC resistance (loop resistance) increase in a spiral braiding?

Yes, it will. But it will be very little increase.

If it does, will this have an effect on Luma and the color differences - essentially reducing the component signal level - considering no AGC?
-Rommel

No. The drop resulting from the resistance increase will be very, very small.
What the shield resistance increase does to loop intercepted external e/m fields is a different story.

What really scares me with this style of construction is this: by flexing the cable, it is possible to either connect or disconnect neighboring conductors, and that will indeed affect the width of the continuous metal, which will in turn affect the eddy currents within the wires. Enough flexing, and it is possible to change the characteristic impedance locally, and not uniformly around the cable, but on a side... That assymetry in the coax lends itself much more to external influences...

I really love the spiral construction for normal work with audio, as it is so easy to strip and connect the shield..but for apps requiring a good transmission line, I would stay away from it.

I cannot answer how it would affect chroma...I can't speak very intelligently about the color burst/chroma/luma time coherence issues.

Cheers, John

 

[Unregistered]

So what is a good brand of cable for HDTV component length of about 30feet?

Is Belden cable good for this?

 

[tsteves]

Belden?
Naturally. Others too. 30 feet is not so long at all for good cable.

 

[Unregistered]

short cables

how much would you pay for a set of short component video cables? they just need to go from my dig cable box or dvd player to my tv... less than 3 feet.

 

[Leprkon]

price for comp cables

$ 28.99 ( 5 bucks cheaper if you go 3 feet instead of 6)

http://www.impactacoustics.com/product.asp?cat_id=601&sku=27082

or

$ 78 if I wanted to impress someone

http://www.axiomaudio.com/component.html

or

$ 24.40

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=181-672

any of those guys will get you hooked up with cables at least as good as the mid-line Monsters at 25 to 60 % of the price....

 

[mitch57]

What do you think of Impact Acoustics top of the line cables?

 

[Leprkon]

Impact Cables

I don't have a set of the Sonicwave cables, but they are some great eye candy and do have the multi-split RCA jack. The splits will help the cable maintain a tight connection longer than the single-piece Velocity series. There's also some additional shielding (three layers compared to two) but you might have to import some interference to a normal set-up to justify the need...

I doubt you would see any instant improvement in video quality over the Velocity series, but it would be more of a long-term investment. You'd also have the damn they look cool factor going for you.