A Discussion On Video Cable Construction

rbinck

The question comes up repeatedly about the price of cables making a difference or not. Why spend big bucks for no apparent gain? Many people do not find any difference in the PQ of expensive cables and the lower priced brands and so forth.

So I thought a thread that focused on the engineering look at the construction of cables and the reasons behind the differences would be in order.

The bulk of the information required to get a pretty complete technical knowledge of the details is located here: http://www.audioholics.com/techtips/audioprinciples/interconnects/ComponentVideoCables.php and it is one of the best series of articles I have seen on the subject. However it is very technical and difficult for many laymen to comprehend.

Here are some excerpts of the paragraphs that are very technical in the article I pulled out that hits the main points of the paragraph:

Quote:

1.0 ENGINEERING 75-OHM INTERCONNECTS Unlike audio cables, which only conduct low frequency data on the order of 20Hz to 20,000Hz, video cable must transmit higher frequencies up to levels of around 8MHz to 10MHz for NTSC and for over 35MHz for HDTV. 2.0 SIGNAL LOSS Signal loss or degradation, can occur from a number of factors which include internal impedance, Electro Magnetic Interference (EMI) including EMI in the Radio Frequency range (RF noise), mismatched impedance, flawed basic cable designs or inconsistent/bad manufacturing. 2.1 Internal Impedance of 75-ohms In a standard audio cable for example, the internal impedances are between 35-ohms and 50-ohms. However, if audio cables are used in place of component video cables, or poorly constructed component video cables are used that are not a true 75-ohm characteristic impedance, the lower impedance value of these cables may result in a partial signal reflection do to a mismatch in impedance, depending on the length of the cable. 2.2 Electromagnetic Interference (EMI) Electromagnetic Interference (EMI) is around us at all times. It comes from radio towers, sun spots, cell phones, modems, remote controls, computers and a number of other signals that are generated from most electronics used in every day life… … It is possible for stray signals from EMI to find their way into a video cable and therefore, create a false signal or internal noise within the component video cable. The result can range from very minor to significant depending on the noise origination and strength. A quality 75-ohm shielded video cable implements several methods to minimize EMI from entering into the cable. 2.3 Mismatched Impedance Thus for component video cable, transmission line effects of any cable lengths beyond 3 meters (remember 1/10 of 30 meters) must be considered Since the source is a 75-ohm impedance, this reflected signal is sent directly back to it creating a delay effect at certain frequencies. This delay, for example, can show up as a ghost in the picture. Multiple ghosts resulting from multiple frequency reflections can look like ringing around the original image. These reflections can also cause partial signal cancellations at various frequencies corresponding to a partial signal loss resulting in a loss of picture detail or color. 2.4 Skin Effect In fact, if you continue with these calculations you will find that it doesn’t even become an issue until over 1GHz which is significantly higher then audio, component video and HDTV signals. 2.4 Flawed Cable Designs or Manufacturing Techniques http://www.audioholics.com/techtips/audioprinciples/interconnects/ComponentVideoCables_3.php: Pursuing the Truth: The audio and video cable market is filled with a number of scams and fallacies that create confusion among consumers (us). Some ideas to consider when shopping for a 75-ohm cable are as follows: Good Engineering: Try to recognize a design feature that makes sense for its purpose over ones that seem too good to be true and may actually be a marketing scam. For example, there is a new component video cable hitting the market that doesn't use conventional RCA connectors. It actually has a "Bullet Connector" derived for audio cables. Based on the RCA connectors geometry and the governing equations discussed in this article, its design cannot produce near a 75-Ohm termination and is no better than a standard audio rca termination. Since the manufacturer choose to use this type of termination, one must wonder if they choose the correct dielectric and spacing requirements to maintain a cable chacteristic impedance of 75 ohms. If not, this may cause impedance mismatching for cable lengths 3 meters or greater resulting in the reflections and signals loss addressed in Section 2.2. The package alone does not define the cable: Some cable Manufacturers like to package their product in fancy, designer packages. Just remember that the package ends up in the trash and the signal the cable transmits is what you will be living with. The primary purpose of the package is to protect the cable from damage during shipping and receiving from the manufacturer to the end user. It should prevent kinks and bends in a cable which can result in diameter changes that affect the impedance. Bad, inconsistent manufacturing: There are a number of small cable manufacturers to be found on the Internet. Nothing is wrong with a small manufacturer as many of the larger companies once started small. However, it is important that these small manufacturers produce a consistent product. Most cable manufacturers (large and small) hand-solder the RCA connectors onto the cables. This is a valid procedure provided it is done by experienced staff and the solder joints are carefully inspected upon completion. Problems that can occur during soldering are melting of the dielectric, excessive solder, incomplete solder joints and so on. As an example of how soldering can damage a cable, it is worth considering the dielectric. If the low melting point dielectric material is overheated during the soldering process, it can easily melt resulting in a change in diameter. Based on the governing equation for internal impedance, by changing the diameter of the dielectric the impedance of the cable has effectively been changed. Some Manufacturers may have a great design, but if they are inconsistent with their soldering or manufacturing techniques, the cables will also be inconsistent. This can mean that from batch to batch, or from cable to cable, the customer is not guaranteed they are purchasing a quality cable. The following pictures show two forms of solder joints on actual 75-ohm component video cables. These cables were taken right out of their package and the RCA barrels were removed to expose the solder joints. Note the lack of quality in the one on the right defined by the inconsistencies in the solder joint. Both cables were hand soldered during manufacturing, yet it is clear that the cable on the left did not alter the diameter of the white colored dielectric while the cable on the right did. Also, look at the quality of the solder joint in the left side cable. There are no solder bulges, dielectric melting, or exposed wires. The result is the creation of as near perfect a 75-ohm termination as possible. The cable on the right is another story. It seems that little care was taken to protect the dielectric as seen by the noticeable melting near the end of the green jacket layer. Also, there are exposed conductor wires, no termination protection and the solder joint displays extremely poor quality. With inconsistencies and the multiple diameter changes of the conductor/dielectric on the right, it is obvious this manufacturer created a poor termination and this cable will likely have significant signal loss at certain video frequencies. Pursuing the Truth: Don't be afraid to remove the RCA barrel and inspect these solder joints for yourself. The connector barrel usually unscrews and can be slid down the cable without damage. Some manufacturers hard mount the RCA barrels by placing shrink sleeve over them or implementing other methods so they cannot be removed. These manufacturers may be so bold as to express elaborate reasons for doing this, but the bottom line is that if you cannot inspect their solder joints, you should use caution when selecting their cables.

This website has many other articles on cables, see: Cable Info
Center

The remainder of the series is pretty easy to follow and I would recommend you read it if you are interested in information about cables.

A very good alternative to premade component cables that is used by many installers that prewire homes for home theater applications is RG6 quad coax cables. This cable is considered overkill for many, but considering the cost and the ruggedness of the cables, it is some of the best cables to use. We use a standard F connector attached to a F to RCA adapter to plug into the equipment. Many people do not like the RG6 because of the stiffness of the cables, but once it is routed neatly, it is fine.

maximus

Excellence...that picture really drives home the point.

ja2935

Another point to notice about the connector on the right is that the shielding is broken so that the core conductor is effectively unshielded for the last few millimeters. The one on the left has the metal outer casing extending the shielding back past the solder joint. If three connectors like those on the right were connected close together, as in most jack panels, they would possibly interfere with each other as well as being susceptable to external EMI (Electro-Magnetic Interference). By the way, crimped connectors are better as no thermal stressing is introduced and a consistent joint is assured.

maicaw

Here is a quote form another article on http://www.audioholics.com/techtips/...ble_budget.php a little off topic but the message seems relevant For even HDTV reasonable deviations from nominal impedance will usually be found under the hood in these electronic units because it's really not that critical at 37Mhz video bandwidths with 2 and 3 meter cables-even RCA plugs eg. are not designed to be 75 ohm - probably more like 35 (compare to BNC or F conn)..IMHO

Akira

while the picture on the right is cheap rca and a bad example, high end studios cut the ground wire off just short of the terminating plug. pin 3=cold, pin2=hot, pin 1 is left cut off. the reason for this is to avoid ground loops in an installation which may have thousands of connections in a small area. since AC (power supply) is a critical factor in equipment performance, every piece of gear is separately grounded to a central "spike' which is literally driven into the ground, thus the physical metal of all components are melded together and ground loops are eliminated by cutting off the shielding and using two conductors instead of three.
p.s. while i like the speed of a crimping set, i don't know of a single high end facility which does not use solder. soldering is a skilled art (which is why i was fired from Bryston amplifiers) which when done properly is the best connection possible.

ja2935

In the aerospace industry both crimping and soldering are used but the soldering is usually automated (solder bath for machine populated PCBs). Crimping is often used for individual wires into pins for multipin connectors. Crimping produces a consistent molecular level bond as the pressure is so high.

Akira

all of the high end consoles are automated solder bath, while some crimp multipins, solder is still the method of choice...the vintage neves and midas are hand soldered, and while always deemed superior...went out of business.
bryston still hand solders...that's their belief and they are as high end as you can get.

stchman

As I have stated before in this forum, the connectors are the weak link in your interconnects. RCAs are just not that good. RCA connectors are good for basedand video and audio. They can also handle component video from HDTV, but not much more.

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Mark Pettit

For long runs (over 12 feet), use RG-6 and F to RCA adapter. Don't buy ready made Radio Shack cable. Buy only high quality cable with shielding. I have installed many systems with RG-6 and the loss is less than standard RCA cables six foot or less. The F to RCA adapter has little loss.

On my personal Toshiba HD TV, I have a twenty five foot run on Component Video.

I think you will find this is less costly and higher quality than any mega cable you can buy.

edders

"Both cables were hand soldered during manufacturing, yet it is clear that the cable on the left did not alter the diameter of the white colored dielectric while the cable on the right did."

There are two dielectrics in each picture. The one surrounding the center conductor and the one surround the shield. The one around the center conductor looks fine to me. The one around the shield has to be the way it is due to the kind of connector used. It looks like a plastic affair and is deffinately cheaper but should not create a serious impedence missmatch.

To use an example I am sure you are aware of from audio clinics, just remove the case on your gear and see if the internal wiring is as pure as you are striving for your external cabling to be. Have you ever actually tried measuring the output inpedence of various audio/video gear, it does vary.

However, I find your article very good and highly praise you for your discussion.

daleb

Radio Shack sells RG-6. Granted, you might do better on the bulk (which they sell) price elsewhere.

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bobinchico

I did some extensive research on articles about cables. I found the following site extremely informative:

http://www.bluejeanscable.com/articles/index.htm

I found these articles easier to read than the link provided at the beginning of this thread.

I ended up purchasing a 6 foot HDMI cable for under $27 (includes shipping). The reception is excellent.

daleb

I always considered Bluejeanscable to be about the best for the money. I do want to get into a pi%%ing contest about $5 cables looking or sounding just as good. People spend money for all kinds of reasons, some like quality construction of products for reasons that are not that obvious at first glance like superior workmanship, better shielding and jacketing, etc. etc.

What's more important is their cables are about 1/2 to 2/3rds the price of Monsters, so if you think BJC is overpriced.. look no further than your local BB or CC for some highway robbery.

Anyway, be aware the HDMI cables they sell they DO NOT manufacture like their analog cables. I can not tell you they are better than cheaper HMDI cables.
But they do know cables, and they provide a lot of interesting information. Maybe you will pay too much for them, maybe not, but I'm betting you have a good cable.

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fryet

Looking at their prices for their HDMI cables, you pay less than you would for Monster cables, so you get better quality for less price. Reading through their articles has made a believer out of me.

bob0426

I just finished reading this thread and the Blue Jeans Cable articles and I wanted to thank ALL of you in this thread for your comments and input. You guys really helped me with my questions concerning cabling.