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CABLE CONSIDERATIONS FOR 1080P/50
Have you heard about 1080p/50? This is the ‘next step' in video. It is double the resolution, and double the bandwidth, of 1080i or 720p HD-SDI. Surprisingly, it is sowing up on the consumer side more than it is on the professional side. You can easily buy an LCD or other display, or a projector, that will show 1080p/50. You can also buy a BluRay player that will produce a 1080p/50 signal – assuming you inserted a 1080p/50 disc. There are a few dozen of those available.
One thing that doesn't exist is a way to broadcast such a signal. Oh, the standards groups are working on it. And, hopefully, what they finally produce will be backward-compatible with SD-SDI and HD-SDI. 1080p/50 is sometimes called "3g" because is uses a 3 GHz clock producing a 3 Gbps data stream. (This is sometimes confused with 3rd generation "3g" cell phones.)
If you're interested in going to 1080p make sure it is 50 frame. There are cameras that will also shoot 1080p/25. While this is a standard theatrical frame rate, it is half the bandwidth of 1080p/50, back to the same bandwidth as HD-SDI. But, you might well ask, why would anyone want to shoot in 1080p/50? Well, there are a number of very good reasons.
REASON #1. When 1080p/50 becomes a standard, everything you already shot in that format will be more saleable. You can sell it again! You can extend the life of the content you are producing.
REASON #2. Murphy's Law says that, if you shoot today in 1080i, your first customer will want that content in 720p. And, if you shoot in 720p, you will have a customer who wants 1080i. You can convert between these formats, but not very well. Especially with high-motion content (sports, racing etc.) it is extremely difficult to convert from one format to the other. You end up with a tennis ball that is a yellow streak across the net! But if you shoot in 1080p/50, you can down-convert to 720p or 1080i without losing anything, without software trying to figure out where that fast-moving content is going. So you can sell your 1080p/50 content as 720p or 1080i, and when 1080p/50 becomes commercially viable, you can sell it again.
The downside to 1080p/50 is, first of all, more expensive equipment. This may change after a few years, but right now it's expensive. And while there are inexpensive cameras (such as RED) that can produce 1080p/50, or even higher resolution, you have to add on equipment and software to record the signal, edit the signal, add graphics and so on. No doubt about it, 1080p/50 is an expensive alternate.
There are a number of camera manufacturers who offer their 1080p/50 cameras with dual-link cables. That is, you simply use two standard HD cables to deliver the signal. However, there are digital cables (such as Belden's entire line) which are tested and verified to carry an entire 1080p/50 signal.
When you analyze the 1080p/50 signal, however, you will see why many manufacturers of equipment and cable, cannot measure up. The clock is 3 GHz, the data rate is 3 Gbps, but the occupied bandwidth (the Nyquist Limit) is half the clock (1.5 GHz). To assure that this data will pass through equipment, cable or connectors, these have to be tested to the third harmonic of 1.5 GHz or 4.5 GHz.
If you want to find out what the problem is, just talk to your local test equipment vendor and ask him for something to test 75Ω cable up to 4.5 GHz. They will tell you there is no such thing…at least not at 75Ω. Network analyzers and other test gear often go up to 10 GHz or 20 GHz or even higher. But that's at 50Ω. Testing a 75Ω cable as 50Ω is something less than accurate.
In order to get these analyzers to work at 75Ω means you have to purchase a balun, a matching network, to match the 50Ω analyzer to the 75Ω cable (or whatever you are testing). And those are simply not available above 3 GHz. So most manufacturers test their 1080p/50 products to 3 GHz, the second harmonic. Again, not as accurate as you might wish.
Data Rate:
3.0Gb/s
Spec:
SMPTE 424M
Cable Part Number
1080p/50
Ft.
m
179DT
76
23
1855A*
154
47
1855P
127
39
1505A*
215
66
1505F
150
46
1506A*
91
28
1694A*
250
76
1694F
192
59
1695A
217
66
7731A
364
111
7732A
289
88
7732LL
354
108
Table 1
Manufacturers who wish to enter the real world of 1080p/50 must buy custom-built matching networks, which can cost many thousands of dollars. And, if they only buy one or two, then obviously, they are not using these to test the cable except in the lab. The best cables out there have every metre tested, not just an occasional test in the lab.
The one serious consideration with 1080p/50 system designs and installation, is cable distance. Table 1 shows the ‘safe' distance for 1080p/50 (SMPTE 424M standard). Note that with smaller cables, these distances can be significantly short, requiring the use of larger cables. However, these distance are calculated from the SMPTE formula that states, when the signal is down -20 dB at half the clock (1.5 GHz), that's as far as the cable can go.
Many chip and equipment manufacturers complain about this limit and state, or show at tradeshows, cables going much farther, up to double the distance shown. This clearly shows that these distances are chip-dependent. As chip designs improve, the distance achievable on any cable will also improve. At the same time, manufacturing process for cable are also improving, so these distances shown are even more "conservative".
If you use this table, you will be very safe. If you use the recommendations of chip or equipment manufacturers, be sure that you maximize the performance potential of every piece to maximize the performance of you system.
About the Author
Steve Lampen has been with Belden for 19 years and currently is Multimedia Technology Manager and Product Line Manager for Entertainment Products. He has an FCC Lifetime General License (formerly an FCC First Phone License) and is a BICSI Registered Communications Distribution Designer. His latest book "The Audio-Video Cable Installer's Pocket Guide" is published by McGraw-Hill.
Visit our web site www.beldenapac.com or email us info@beldenapac.com
I've got the balun transformer connected to the TV antennae. How do feed it into the plug on a car radio?
From antennae, to coaxial cable, to balun transformer.
How to feed into the plug on a car radio?
not sure good q
good luck
SVB96HB Installation with video balun and Cat5e cable
