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Cable Asylum Interconnects, speaker wire, power cords. Ask the Cable Guys. |
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In Reply to: Sharing some explanations on video cable specs ... posted by SteveLim on August 1, 2006 at 22:56:56:
Specifications are all very well and fine, but they do not tell the whole story.All of the specs mentioned above were obviously looked at with strictly video/RF in mind, and the importance of those specifications for video/RF use, and generally, for use with fairly long lengths (hundreds and thousands of feet), rather than the several feet to 20-30-50 feet that is used around the house in consumer applications.
First of all, most of those specs, in and of themselves, mean absolutely NOTHING with respect to the cables use for analog line level signals and the sonic performance they will have.
Second, even if we restrict ourselves to the intended use of those specs, and examine their application to the analysis of cables that WILL be used to transfer video or RF, not all of the specs have the same priority, or put another way, they should not all be weighted equally. Some of the cable parameters are only incidentally of concern, and others are of concern, but for reasons not immediately obvious, nor directly connected to the basic or primary parameter metric.
There are also some questionable statements made within the text you copied from the AV site, and again, their comments ONLY apply to video/RF use, and not for audio use AT ALL, for instance:
" None of the video RCA connectors surveyed were 75 ohm - but several manufacturers in the years since the survey corrected this with true 75 ohm RCAs, .... "To the best of my knowledge, the ONLY RCA that actually reaches a true 75 ohm impedance, is the WBT Nextgen plug used in conjunction with the matching WBT Nextgen jack. You MUST use BOTH the WBT Nextgen plug AND the jack in order to maintain the benefit of a true 75 ohm characteristic impedance. Use a regular RCA jack, and the plug's benefit's are lost.
So their statement is in error, and only confuses the issue of RCA plug Z.
AND
"Excessive resistance in a cable will attenuate the signal."This is true, but is typicaly not a signficant factor for home use.
The most strenuous use of a coaxial cable in the home is the run from a satellite dish, and this is an extremely high RF frequency, AND a fairly long run is involved, say 50 to 100 feet. As such, the overall cable parameters have more to do with the loss of signal at these frequencies than JUST the resistance. Yes, if you use a VERY small center wire, then there will be some losses for runs that are longer than a few dozen feet, but usually these losses will occur all across the band, and will not favor one frequency or another that much.Typically, if the run is NOT a 50 foot run, and/or the signal is NOT from a satellite dish, the the resistance of the center wire will not be a significant factor. There are always special circumstances, or specific situations, such as the satellite dish, that might actually benefit from less resistance, but on the whole, even for vidoe and RF, unless you are doing something atypical, the resistance of the coax center wire will not be a problem.
"Velocity of Propagation is what you most often see in a catalog, and comparing VP between cables gives you some idea of which cable performs better at high frequencies. A faster velocity means less high-frequency loss and flatter frequency response overall."
This is just plain wrong. A higher velocity of propogation DOES NOT mean less high frequency loss and a flatter frequency response. WRONG.
There are other questionable statements about the various parameters, but these are the worst.
I am short for time right now, but I will post a continuation of my reply as time permits, probably this weekend sometime, and try to cover some of the coaxial cable parameters, and what they have to do with video, and how they might relate to audio use (if at all).
I will also address your summary points, as it would probably be helpful to you as well as others reading this.
Jon Risch
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Follow Ups
- Those pesky specs - Jon Risch 21:24:56 08/03/06 (0)
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