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Composite vs. Component Cables
I haven't seen a published spec for RCA connectors since they are virtually
never used for anything but low frequency applications when their reactance is negligible. They are not appropriately used for RF applications. They can. however, be measured and thus characterized like any other physical object to specify how they behave. Just as their ohmic resistance can be measured with an ohmmeter, their reactance can be measured (as a function of frequency) to see if they are capacitive, inductive, or have negligible reactance. The results of these two measurements are combined (vector summed) to form the impedance. Like virtually any other connector, RCA connectors have insulators which separate the (center) terminal and ground, and this insulation has a dielectric constant which will be very different if the insulator is Teflon versus something cheap like Bakelite or cardboard. An ohmmeter will not see this difference, but a 2 GHz RF signal certainly will. RCA connectors, like many other types of connectors are not specified this way since they are not intended to be used this way, just as a Molex power connector is never characterized with this specification. The fact remains, however, (and this was my original and only point in replying to your erroneous statement) that an RCA connector (as well as a piece of wet spaghetti) has a characteristic impedance. The phrase simply means that it displays resistive and reactive components (which vary as a function of frequency) and these collectively characterize the device / object, just as explicitly as an Amphenol PL-259 RF connector does. Smarty "Matthew L. Martin" wrote in message ... Smarty wrote: Every connector has a characteristic impedance. It's basic physics. As you may be aware, an impedance in nothing more a resistive component Please cite the impedance specification for an RCA connector. Matthew -- Thermodynamics and/or Golf for dummies: There is a game You can't win You can't break even You can't get out of the game |
Composite vs. Component Cables
You really have some very confused concepts going on here. Take a cable
which is a small physical length relative to the signal it is attempting to pass. Put connectors on it which exhibit considerable reactance. Try to get the signal injected at the input to show up at the output. Let's, for example, use an RCA cable which has a few picofarads of capacitance due to its insulator being made of cheap plastic (as opposed to glass or Teflon) and put a high frequency signal into it. Let's try 5 GHz. The connector's shunt capacitance at this frequency makes it look like a dead short circuit. The cable length beyond the connector will be of little or no consequence, since the characteristic impedance of the RCA connector creates a huge impedance. The length of the subsequent cable is of little or no importance, but transmission line theory and Smith Charts would allow a very accurate prediction of the combined effect if both the RCA connector's characteristic impedance as well as the cable's characteristic impedance and attenuation factors are known. Smarty "Matthew L. Martin" wrote in message ... Grant Edwards wrote: On 2006-11-05, Matthew L. Martin wrote: On 2006-11-05, Wes Newell wrote: I had a discussion with a techie friend of mind, who claimed that there was no PHYSICAL difference between a "composite" cable bundle and a "component" bundle of three cables (i.e. the only difference being the kind of signal that is sent down the wires). They are physically interchangeable. Is this correct? I wasn't going to reply to this, but since no one wants to give you a simple answer, it's yes. The only difference other than wire size is the color of the connectors. Each consist of 3 shielded rca cables. Except that the impedance of the cable makes a difference. You can't just use anything with RCA connectors on the ends and expect good results with high-bandwidth signals. RCA connectors don't have a characteristic impedance. If you are using them, then you are more interested in shielding than impedance. Where did I say anything about the RCA connectors having a characteristic impedance?? Since they don't have a specified characteristic impedance, the impact of an impedance mismatch is expected to be negligible, especially when the 1/4 wave of the carrier is much longer than the cable length. Matthew -- Thermodynamics and/or Golf for dummies: There is a game You can't win You can't break even You can't get out of the game |
Composite vs. Component Cables
Smarty wrote:
I haven't seen a published spec for RCA connectors since they are virtually never used for anything but low frequency applications when their reactance is negligible. They are not appropriately used for RF applications. If there is no spec, there is no characteristic impedance. No two RCA connectors need be anywhere near alike. The simple fact is that when RCA connectors are used, shielding is far more important than the characteristic impedance of the connection Matthew -- Thermodynamics and/or Golf for dummies: There is a game You can't win You can't break even You can't get out of the game |
Composite vs. Component Cables
Don't you understand? Characteristic impedance is a quantified / measured
value no different from voltage, length, or mass. An RCA connector has all 3, as well as many more characterizations. Everything ***can*** be characterized by measurement, and yet it doesn't always make sense to do so. Nobody, for example, is interested in the impedance of a sheet metal screw and therefore you seldom would see it measured or published. Similarly, the length or the mass of a resistor is seldom characterized since these are not the important specifications. RCA connectors have a characteristic impedance just as a wet piece of spaghetti has a characteristic impedance if you choose to measure it. Nobody cares, and thus the characteristic impedances for these 2 items are not typically measured or published. Thus, I can't show you are reference on the web or other citation, but I could certainly measure the characteristic impedance of either. The original and final point I have been making all along here is that your original reply to the post stating that RCA connectors do not have a characteristic impedance is false. They do, but it is not generally of interest since the connectors are used mostly at low frequencies where their impedance effects are negligible. At hi def frequencies, these effects cannot be ignored. Cable is a "distributed" impedance with its' reactance and resistance distributed linearly along its' length (unless the cable is damaged, crimped, or otherwise not lying undistorted in free space). An RCA (or any other) connector is a "lumped" impedance which can and will cause an impedance discontinuity if installed on a length of cable, regardless of its' length and regardless of the frequency of use. The severity of the impedance mismatch and the resulting reflections / attenuation / phase distortion / delays can only be correctly described by taking all of these effects into account. There are textbooks on transmission line theory which are devoted to these topics. You can oversimplify the process and state: The connector has no impedance" or "The 1/4 wavelength stub is too short" or some other such statement which reveals a lack of understanding of what is truly the physical phenomena. If you do, I will step in, as I did, and provide a correct explanation. Smarty "Matthew L. Martin" wrote in message ... Smarty wrote: I haven't seen a published spec for RCA connectors since they are virtually never used for anything but low frequency applications when their reactance is negligible. They are not appropriately used for RF applications. If there is no spec, there is no characteristic impedance. No two RCA connectors need be anywhere near alike. The simple fact is that when RCA connectors are used, shielding is far more important than the characteristic impedance of the connection Matthew -- Thermodynamics and/or Golf for dummies: There is a game You can't win You can't break even You can't get out of the game |
Composite vs. Component Cables
"R. J. Salvi" wrote in message ... Oops, I did miss the point. However -- and to pick nits, he wasn't "asking whether a cable labeled for composite use could be used for component signals," rather whether the composite three-cable bundle of audio/video, could be used as a substitute interface for a component video connection. Bzzt, picking the wrong nit there. He asked if the cables were physically the same, presumably so he could use his old composite cable in a component setup and save a few bucks. For a short run, it should be fine. -- RJ "Elmo P. Shagnasty" wrote in message ... You missed his point. He was talking about the physical cable, not the signal that's sent down it. He was asking whether a cable labeled for composite use could be used for component signals. - - - In article , Julian wrote: I had a discussion with a techie friend of mind, who claimed that there was no PHYSICAL difference between a "composite" cable bundle and a "component" bundle of three cables (i.e. the only difference being the kind of signal that is sent down the wires). They are physically interchangeable. Is this correct? In article , "R. J. Salvi" responds: From: http://www.edmundoptics.com/techSupp...?articleid=297 Composite vs. Component Signal: Color video signals are composed of luminance and chroma information. Composite signals carry both luminance and chroma on one line, whereas Y-C and RGB signals carry luminance information on one line and chroma information separately on one or more lines. Breaking up the signal components generally improves signal fidelity, especially when recording or balancing color. |
Composite vs. Component Cables
In article , Jim Gilliland
wrote: Julian wrote: I had a discussion with a techie friend of mind, who claimed that there was no PHYSICAL difference between a "composite" cable bundle and a "component" bundle of three cables (i.e. the only difference being the kind of signal that is sent down the wires). They are physically interchangeable. Is this correct? The basic answer is NO, they are not equivalent. Component video requires three 75 ohm cables. Composite video requires only one. There is no requirement for the two audio cables in a composite bundle to be 75 ohm cables, so you have to assume that they are not. I'm not sure why we're seeing all the discussion about RCA connectors. The connectors aren't the issue. The characteristic impedance of the coax itself is what matters. I'm also not sure why we're seeing any discussion of twisted pair. The audio cables in a composite bundle are coaxial cables. They're just not the right coaxial cables for video. O.K. you guys. I now think I have the answer I was looking for. They are basically the same (in a physical sense) except that "component" cables are normally of a higher quality than "composite" cables, and therefore (normally) command a somewhat higher price for an equivalent length of cable. Thanks all. -- Posted via a free Usenet account from http://www.teranews.com |
Composite vs. Component Cables
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Composite vs. Component Cables
"JerrySmith'sTightEnd" wrote in message
t... "R. J. Salvi" wrote in message ... Oops, I did miss the point. However -- and to pick nits, he wasn't "asking whether a cable labeled for composite use could be used for component signals," rather whether the composite three-cable bundle of audio/video, could be used as a substitute interface for a component video connection. Bzzt, picking the wrong nit there. He asked if the cables were physically the same, presumably so he could use his old composite cable in a component setup and save a few bucks. For a short run, it should be fine. Please re-read my post...I admitted missing the original point, but for good reason. There's a fair amount of latitude exercised describing cable differences when the term "PHYSICAL" is used, as used by Julian (original poster). R, L &C, dialectric, terminations, gauge, shielding and design, etc. And judging by the diversity of responses to the original poster, I'd say there was a fair amount of interpretation on the subject in general. The fact that Julian used the term "bundle" when referring to composite cable(s), lead me to believe his understanding of the differences between composite and component was blurred. Hence, I copy/pasted a definition illustrating the signal differences between composite and component, presumably to illuminate their lack of interchangability (composite is comprised of one cable, component, three). Fwiw to Julian...I am using a Radio Shack 3-cable A/V composite video, stereo audio bundle (don't know the catalog number), as a component interface between my DVD player and DLP. Works great. -- RJ |
Composite vs. Component Cables
I think the main factor would be the capacitance between the center conductor an
the shield. No sure if that applies here, but the higher the frequency sent through the cable, the more its natural capacitance comes into play. -- All the Best Richard Harison "Smarty" wrote in message ... Don't you understand? Characteristic impedance is a quantified / measured value no different from voltage, length, or mass. An RCA connector has all 3, as well as many more characterizations. Everything ***can*** be characterized by measurement, and yet it doesn't always make sense to do so. Nobody, for example, is interested in the impedance of a sheet metal screw and therefore you seldom would see it measured or published. Similarly, the length or the mass of a resistor is seldom characterized since these are not the important specifications. RCA connectors have a characteristic impedance just as a wet piece of spaghetti has a characteristic impedance if you choose to measure it. Nobody cares, and thus the characteristic impedances for these 2 items are not typically measured or published. Thus, I can't show you are reference on the web or other citation, but I could certainly measure the characteristic impedance of either. The original and final point I have been making all along here is that your original reply to the post stating that RCA connectors do not have a characteristic impedance is false. They do, but it is not generally of interest since the connectors are used mostly at low frequencies where their impedance effects are negligible. At hi def frequencies, these effects cannot be ignored. Cable is a "distributed" impedance with its' reactance and resistance distributed linearly along its' length (unless the cable is damaged, crimped, or otherwise not lying undistorted in free space). An RCA (or any other) connector is a "lumped" impedance which can and will cause an impedance discontinuity if installed on a length of cable, regardless of its' length and regardless of the frequency of use. The severity of the impedance mismatch and the resulting reflections / attenuation / phase distortion / delays can only be correctly described by taking all of these effects into account. There are textbooks on transmission line theory which are devoted to these topics. You can oversimplify the process and state: The connector has no impedance" or "The 1/4 wavelength stub is too short" or some other such statement which reveals a lack of understanding of what is truly the physical phenomena. If you do, I will step in, as I did, and provide a correct explanation. Smarty "Matthew L. Martin" wrote in message ... Smarty wrote: I haven't seen a published spec for RCA connectors since they are virtually never used for anything but low frequency applications when their reactance is negligible. They are not appropriately used for RF applications. If there is no spec, there is no characteristic impedance. No two RCA connectors need be anywhere near alike. The simple fact is that when RCA connectors are used, shielding is far more important than the characteristic impedance of the connection Matthew -- Thermodynamics and/or Golf for dummies: There is a game You can't win You can't break even You can't get out of the game ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Composite vs. Component Cables
On Mon, 6 Nov 2006, Julian wrote:
O.K. you guys. I now think I have the answer I was looking for. They are basically the same (in a physical sense) except that "component" cables are normally of a higher quality than "composite" cables, and therefore (normally) command a somewhat higher price for an equivalent length of cable. As a first-level approximation, this is correct. Component cables will generally "work" if used as a composite cable. That does not mean that this is a preferred, or suitable, use. But, if the choice is between using a component cable or nothing, then use it. A good layman's metaphor is that using a composite cable as a component cable is like using junk food as food. Junk food will quell your hunger pangs, and it will deliver some amount of nutrition. Junk food is also certainly better than starvation. On the other hand, a diet of junk food is generally not good daily nutrition, nor is it good for you in the long term. This is different from the issue of "Monster" cables, which are generally ridiculously overpriced and quite unnecessary. A "Monster" cable is the equivalent of a $1000 restaurant meal; it may be "better" than an ordinary meal cooked at home, but the price/performance favors the home cooking. Home cooking also wins price/performance over junk food; junk food is convenient but not particularly cheap. It's all based upon what the cable is being asked to do. Delivery of an analog audio signal to a modest amplifier and speakers is not a particularly strenuous task for a cable; even the smallest and cheapest cables will do. Delivery of RF or video signals requires somewhat more from a cable; and inadequate cables will not perform as well. The impact ranges from the unnoticable to distortion or loss of performance. Case in point. When receiving satellite TV in a fringe area, a better cable between the dish and receiver will deliver a usable signal about 300 miles further out than an inferior cable. Or, under adverse weather conditions, a better cable will deliver a usable signal when an inferior cable will not. A component video cable delivers analog video, albeit in one color (and thus making HD possible). It's like RGB, only different. :-) If a composite cable is used, two of the lines will probably have a signal of inferior quality to the third. Depending upon your equipment you may, or may not, notice the difference. As long as you don't buy a "Monster" cable, a good-quality component video cable is relatively inexpensive compared to the rest of your system, and in my opinion it is false economy to use a composite cable as anything other than a temporary shim prior to the acquisition of a proper component cable. As a final aside, let's talk about digital cables (DVI or HDMI). With digital signals, either it works or it doesn't. If you have a $20 digital cable that works, you aren't going to get better performance by buying a $150 "Monster" cable. This is an excellent example where you can save your money. Similarly, it's obvious if a digital cable fails. Supposedly, the "Monster" cables are less likely to fail, but I have never had even an el cheapo digital cable fail barring physical abuse. Analog cables, such as component and composite cables, may have less catastropic failures that are less obvious as cable failure. I hope that this information is helpful. -- Mark -- http://panda.com/mrc Democracy is two wolves and a sheep deciding what to eat for lunch. Liberty is a well-armed sheep contesting the vote. |
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