Composite vs. Component Cables
 

I entirely agree. The shunt capacitance of the insulating dielectric at the
connector looks like a short circuit at high frequencies, and at lesser
frequencies acts as a low pass filter.

Smarty



"Richard Harison" wrote in message
...
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





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Composite vs. Component Cables
 

Smarty wrote:
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.


Then tell us what the characteristic impedance of an RCA connector is.
If you can't, stop typing nonsense.

Is it not true that when RCA connectors are used, the shielding is more
important than the impedance of the interconnect?

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
 

While it is indeed true that cables carrying digital signals (such as DVI)
most often either "work" or "don't work", the signals they are passing are,
in their spectral content, the same as analog signals, and, in fact, have
rise times and fall times which make their pulse edges exactly look like a
(non infinite) series of analog waveforms rather than a true (idealized)
pulsed waveform. Degradation to the digital waveform in a cable is not
simply absent or present. In the same manner as analog transmission in a
cable, the line and the connector act dispersively, add differential phase
delays, differential amplitude attenuations, and phase / time distortions
which can, and ***will** distort the waveform. The signal recovered at the
end of the wire is indeed different from what is sent, and, for long lines,
or poorly matched cables / connectors / driver electronics distorted to the
point where it can become unusable.

To the extent that manufacturers have chosen adequate wire and connectors
for a given length, signal strength, etc......this problem is not normally
visible to the consumer. Thus, most cables appear to either work or not
work. Again, at the risk of seeming academic, the laws of physics still
apply, and cables can and will truly degrade digital signals, in some cases
to the point where they are unusable or badly distorted.

Smarty
"Mark Crispin" wrote in message
nda.com...
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.

Composite vs. Component Cables
 

Matt,

This is not nonsense. This is basic electrical engineering. The impedance of
an RCA connector, if I had to take an educated guess, would be 10s of
megohms resistive and no less than 10K ohms reactive (capacitive) at the
frequencies we are discussing. It is entirely clear that you will have not
even a clue as to what this means.

Smarty



"Matthew L. Martin" wrote in message
...
Smarty wrote:
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.


Then tell us what the characteristic impedance of an RCA connector is. If
you can't, stop typing nonsense.

Is it not true that when RCA connectors are used, the shielding is more
important than the impedance of the interconnect?

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
 

Matt,

Shielding in the cable itself becomes important if the cable sits in a noisy
environment, in which case the shield (which is nominally grounded) serves
to prevent noise. Moreover, in multiconductor cables like component, RGB,
etc......the shield reduces "cross-talk", the tendency of the emitted
electromagnetic field arising from one conductor (let's say green, for
example) to corrupt the neighboring signals (for red and/or blue).

The connector's impedance becomes an issue if it begins to either attenuate
(differentially) the signal such that higher frequencies become more
attenuated than lower frequencies, or, if the impedance of the line itself
is in the same range or higher than the connector impedance. To use a crude
plumbing analogy.......a 1 inch pipe with low impedance to water flow would
be severely impacted by connecting it through 1/4 inch connectors which
present a large impedance to the water flow.

Neither effect is necessarily more or less important. It requires an
understanding of the physical phenomena and how they relate. The simple (and
sometimes incorrect) answer is that RCA connectors for component video will
most often suffice. And this is true despite their characteristic
impedance................


Smarty


"Matthew L. Martin" wrote in message
...
Smarty wrote:
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.


Then tell us what the characteristic impedance of an RCA connector is. If
you can't, stop typing nonsense.

Is it not true that when RCA connectors are used, the shielding is more
important than the impedance of the interconnect?

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:
Matt,

This is not nonsense. This is basic electrical engineering. The impedance of
an RCA connector, if I had to take an educated guess, would be 10s of
megohms resistive and no less than 10K ohms reactive (capacitive) at the
frequencies we are discussing. It is entirely clear that you will have not
even a clue as to what this means.

Look, if there is no specification for the impedance of an RCA
connector, as there are for many cable ends when characteristic
impedance is important, then it isn't important.

Why can't you admit this?

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
 

"Jim Gilliland" wrote in message

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.

I am looking at an AV cable that came with an old VCR that I keep on the
computer to copy family tapes to DVD... the audio lines have 24 AWG printed
on them.

This is NOT a coax designation, but the description of a twisted pair.

Composite vs. Component Cables
 

Matthew,

You ask me to "admit" that characteristic impedance is not important for
this specific connector and I can only say that this is true if the
connector is used in the manner for which it was originally intended,
namely, audio and low bandwidth composite video. If it is used
inappropriately for other applications, such as hi def TV, it very well may
be extremely important.

It was not my original contention that it was or wasn't important however.
It was, and still is my only contention that this connector ***HAS A
CHARACTERISTIC IMPEDANCE". This is a measurable, finite, and physically
determined parameter / characteristic, just as a pipe connector has very
specific characteristics. Saying (as you originally did incorrectly) that an
RCA connector "has no characteristic impedance" is the same as saying it has
no length, no width, no mass, etc. My comment was intended to correct that
error, and requires no "admission" on my part of anything.

Smarty




"Matthew L. Martin" wrote in message
...
Smarty wrote:
Matt,

This is not nonsense. This is basic electrical engineering. The impedance
of an RCA connector, if I had to take an educated guess, would be 10s of
megohms resistive and no less than 10K ohms reactive (capacitive) at the
frequencies we are discussing. It is entirely clear that you will have
not even a clue as to what this means.

Look, if there is no specification for the impedance of an RCA connector,
as there are for many cable ends when characteristic impedance is
important, then it isn't important.

Why can't you admit this?

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 Sweeney wrote:
"Jim Gilliland" wrote in message

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.

I am looking at an AV cable that came with an old VCR that I keep on the
computer to copy family tapes to DVD... the audio lines have 24 AWG printed
on them.

This is NOT a coax designation, but the description of a twisted pair.

Not necessarily. The center connector of a piece of coax can be labeled that
way as well, especially if the coax isn't designed to meet any particular
standard.

Then again, it may be twisted pair in the case of your specific cable. It's not
impossible to transfer audio over twisted pair, it's just not a particularly
good idea. But I'm sure there are a few manufacturers that have cut that corner.

In any event, I sure wouldn't try to use those wires (the audio ones) for any
form of video.

Composite vs. Component Cables
 

Julian wrote:
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.

If that's what you took from my post, then you've missed the point entirely.

As I said, the answer is NO, they are not equivalent. They are NOT the same in
a physical sense. The difference is NOT just one of quality. They are
distinctly different cables, and even though they may look the same, they behave
differently. They are not interchangeable.

In some circumstances, you may find that you can adequately pass video through a
short length of audio cable. That doesn't make it the right cable for the job,
and it's very likely causing some degree of degradation.

As another poster pointed out, some manufacturers may use video cable to carry
audio. In that case, the audio cables will work fine for video (for obvious
reason). But without some sophisticated test equipment, you really have no way
of verifying that. So even in this case, you can't safely make that assumption.