 |
|
 |
|
|||||
Coaxial Cable ComparisonsIn some recent discussions over on remotecentral.com, we discussed measuring video cables in terms of IRE units. Typically cables specs are given in deciBels, which is a standard way to measure things in the engineering world. But the question is - How does that relate to what you expect to see on the screen? An IRE unit is a measurement of brightness level, from 0 to 100. Sync pulses will go into negative IRE, down to -40. So using a standard length of 100 feet of cable, and a scale of IRE, we can give an understandable answer as to what you might expect from various cables. One challenging issue is that different cable manufacturers give their loss measurements at different lengths and different frequencies, and some not at all. It is also important to understand the the IRE level you see for a particular image is effected by the type of picture content. A large white block in the middle of the screen will almost always be rendered at the correct IRE level, but fine white vertical lines on a black background will often be some level of gray, and not the full white they are supposed to be. So to understand the table below, when we talk about levels at DC, that would be a large white block, or perhaps full screen white. 1MHz might be some large text, and edge detail performance. 10MHz would be fine text, pinstripe suits, fine hairs silhouetted against a bright background, etc. The highest detail possible in 720p and 1080i is around 35MHz. 75MHz is beyond what most display can resolve, and is for comparison purposes. In this first table, we have the single coax cables. The results are the calculated IRE level after 100 feet of the given cable.
In the next table are the multi coax bundles. Since they are typically smaller diameter cables with smaller conductors and higher capacitance, they typically don't perform as well.
You can see that the Canare L7CFB is a real champ, and slightly beat out the Belden 1694a. However the Canare is a real firehose at 0.402" diameter, and is around $700/300M, where Belden 1694a is around $475 for a similar length and is standard RG6 diameter (0.274"), and is no doubt easier to handle. A more comparable Canare cable is the L4CFB, which you can see is not quite as good as the Belden. If you are a cable manufacturer and would like to see how you cable stacks up to these cables, send an email and we'll add it on.
|
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
©2006-2008 NeoProIntegrator.com |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||