The photo on the June cover of Broadcast Engineering is courtesy of Andy Washnik, CORPRICOM.
Back me up
If you back up your data to the same physical hard drive and the drive fails, won't everything be lost?
Brad Gilmer responds:
Backing up a drive onto itself is never a good strategy. If the drive or controller fails, the backup is no good.
I recommend that you create at least two logical partitions on the physical hard drive (or install two separate drives if you have room). The first partition stores the operating system (OS) and any other applications that can be easily reloaded from their distribution CDs. The second partition stores application-specific data.
This is a good idea because the performance of some operating systems degrades over time. The only way to get the OS back to normal is to reformat the drive and reinstall the OS. But, not all operating systems suffer from this problem.
If you have the OS on a separate partition from the data, you can reformat and reinstall it without having to restore all of your data. In many cases, you can also reinstall your applications to the first partition and simply relink to the data drive.
I only back up the second partition on the belief that I can reload everything on the first partition from CDs.
RAID is a good technology to protect critical systems from data loss, but it can be costly, and some applications, like laptops, can't use it due to hardware constraints.
In the May 16 Transition to Digital e-newsletter, the “ATSC transports streams” article says: “In the ATSC system, in order to facilitate channel acquisition in less than a half second, there is a defined relationship between video and audio PIDs for a given program.”
This was present in the original version of the standard (ATSC A/53) and was known as the program paradigm. The program paradigm was dropped from the standard in later versions. The video and audio PIDs for each program are listed in the program map table for that program and referenced in the service location descriptor of the virtual channel table.
New York, NY
CAT5 cable is most commonly a four-pair cable. It is possible to get hundreds of pairs of CATx cable under a single sheath. (Behind four-pair, 25-pair seems to be the most common for CAT5.) CATx ratings do not necessarily specify twist density or direction. I hear that a cable must simply meet the performance specifications and how those specifications are met is up to the cable manufacturer.
Brad Gilmer responds:
You are correct. CAT5 cable is available in different configurations. Multi-pair cables are commonly used to run between floors and patch bays or where multiple Ethernet connections are required. Four-pair cable is used frequently in point-to-point Ethernet wiring.
All the cable manufacturer must do is meet the specifications. That said, they meet those specifications by using a consistent twist-per-inch to create a transmission line with the appropriate characteristics to reliably transfer the data on the cable with acceptable return loss. How they do that is left to the manufacturer.
Editor's note: Broadcast Engineering will begin a three-part series on wiring and cable by Steve Lampen in September. Cable specifications, selection and usage for audio, video and Ethernet applications will be covered in this series. Don't miss it!
Q. Provide the introduction years for the following SD digital tape formats: D1, D2, D3, Digital Betacam, D5, DV and MiniDV, DVCPRO, DVCPRO50, D9 Digital-S, DVCAM, Betacam SX, Digital8 and IMX.
A. The correct answers are from Graham Jones' book, A Broadcast Engineering Tutorial for Non-engineers; pages 147-149:
|DV and MiniDV||1995|
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