Listen Here  

Direct DownloadSubscribe via RSSSubscribe via iTunesSubsribe with Zune

The Custom Integrator Show Installment 007 is live. In this installment, we finally start to dive into one of the more troublesome aspects of the Windows Media Center ecosystem – Digital Cable Tuners (DCTs). The more common nomenclature is OpenCable Unidirectional Receiver (OCUR), but Microsoft now refers to them as DCTs (while Niveus references their products containing DCTs as DCRs – Digital Cable Receivers). Many integrators criticize Microsoft for their CableCARD implementation and find it to be cumbersome and convoluted. Putting it into perspective, however, one must realize that Microsoft provides the only PC-based platform that even supports CableCARDs (mostly because of the end-to-end protected path that Windows Vista affords). They just have to live by the rules set up by CableLabs and its constituents, which really are a nightmare when you actually dig down into the guts of them. Granted, it is not exactly easy to get it up and running well, but if it is installed and configured properly, it does actually work – and work well. This installment covers the initial setup and some of the basic steps you need to take as part of ensuring a successful experience. Installment 008 will start to drill down into the technical specifics of the CableCARD pipeline and several steps to take when troubleshooting the platform.

The most difficult part of DCTs and CableCARDs is understanding the architecture. Obviously, the first place to start is with the specifications. Most integrators do not spend the time or commit the energy to read the standards and associated materials, but with CableCARD, it really can make a difference when the bits hit the wire (this is the only good way I have found to learn how the technology really works). There is a list of the ones I recommend reading (or at least reviewing) if you want to get the full picture at http://www.cablelabs.com/specifications/ocOCUR.html. The main one to read and the one that really defines the architecture is at http://www.cablelabs.com/specifications/OC-SP-OCUR-I08-081114.pdf. It is interesting to note that the XML schema examples in Section 8.5 have references to Digital Keystone, Inc. For those that do not know it, DK is the company who actually wrote the firmware in the ATI DCTs. They also supply the web page interfaces to the DCTs when you open them up via Windows Vista’s Network view of the ATI TV Wonder OpenCable Receiver. Obviously, they were instrumental in working with CableLabs on the original specifications. Other documents in the list outline how the Digital Rights Management (DRM) aspects flow with references in those schemas to Microsoft’s DRM platform, which is key to their CableCARD implementation.

Unfortunately, there really is not a whole lot of good documentation on the DCTs themselves, so I will try to wade through what I know about them as a way to help clarify how they work and what to look for when working with them. Before we get to that level though, we must focus on the basics. It is easy to overlook the obvious factors that make up a solid RF plant within the home. One of the more important factors to have within spec is the signal coming into the DCT from the coax and F connector itself. This is true for any device connecting to the coax infrastructure, although the DCTs tend to require tighter tolerances than most set top boxes and the like.

There are two primary measurements that are important.

· SIGNAL LEVEL – This needs to be measured at the F connector going into the DCT with a good RF signal strength tool. If you do not have one, make sure that the cable provider measures it across all frequencies being used by their system and not just a single reading somewhere in the middle. As you know, different channels use different frequencies. You must make sure that the Signal Level is as flat as possible across the entire spectrum. For the ATI DCTs, this needs to be somewhere between -8 dBmV and +8 dBmV (Decibels referenced to 1 millivolt across 75 ohms) for a QAM 256 cable plant. The closer to 0 dBmV value across all frequencies, the better. You cannot go by the numeric values provided by the current versions of the ATI DCT hardware. They are not accurate and will lead you down the wrong troubleshooting path. Although the relative range of values is useful, the actual numbers are wrong.

· SIGNAL to NOISE RATIO (SNR) – The values exposed by the ATI DCTs for the SNR are accurate. The higher the number, the better. They also follow the general guidelines required for the commercial set top boxes on the market:

     Below 29 dB – Unacceptable

     29 dB to 31 dB – Poor

     32 dB to 33 dB – Acceptable

     34 dB or better – Good

There also is good documentation in the ATI DCT installation guide about making sure that both lights on the DCT itself are green before proceeding in addition to some of the other basics to check out. Most of all, make sure that you have excellent terminations of the F connectors themselves. Without ensuring that the basics are taken care of, your CableCARD implementation is almost guaranteed to have problems later.



Leave a Reply