Cable companies (generally referred to as MSOs or multiple-system operators, as most cable companies own and operate cable systems in dozens - or hundreds - of different cities) offer a variety of services. But the crème de la crème of cable services is HDTV over cable, and it's nearly everywhere.
Getting on the QAM bandwagon
The biggest difference between HDTV signals on a cable system and those broadcast over the air revolves around the system used to modulate an HDTV signal for transmission as radio-frequency signals across the cable system.
Broadcast HDTV uses a system called 8-VSB (vestigial sideband), while cable usually uses a system called QAM (quadrature amplitude modulation). What's the difference? Well, the technical specs are for the engineers - what's important to HDTV viewers is that you need a different kind of HDTV tuner to receive QAM signals than you do to receive 8-VSB (though many TVs include a tuner that can tune into both types of signals).
For a lot of people, HDTV cable service comes through an HDTV set-top box (or cable box) that has a built-in QAM tuner.
Encrypting and decrypting
The other big difference between broadcast and cable HDTV concerns encryption and "premium" cable channels. Broadcast HDTV channels - over-the-air broadcasts that you pick up with an antenna - are free for the picking (up). If you receive the channel, you can watch it.
Many cable TV HDTV channels, on the other hand, are considered premium or for-pay content - you have to pay extra every month to receive them. Because of this arrangement, most cable systems use an encryption system that scrambles the signal (using an encryption algorithm, or formula). So even if you have a QAM tuner (whether built into your HDTV or attached to it), you can't watch these programs without some hardware to decode the encryption (in English translated from Geekese, that's unscramble the picture).
In some cable systems, the local broadcast HDTV channels are transmitted across the cable system unencrypted - if you have the appropriate tuner, you can view these channels without some sort of extra decryption hardware.
Most cable HDTV viewers need a set-top box from your cable company to view HDTV. This set-top box handles the QAM tuner duty, connects to your cable company to authorize you as a paying customer, and does the decryption/unscrambling of any premium channels.
Pricing for HDTV set-top boxes varies widely by cable company. Some companies may charge you a monthly rental for the set-top box but nothing for your HDTV channels. Others may not charge for the box rental but then charge you on a per-channel or package basis for HDTV channels - others may have a combination of these two approaches. In many cases, you're required to get the digital-cable packages in order to get HDTV channels beyond ABC, CBS, NBC, and Fox. (Check out your cable company's Web site to find out what they offer.)
Your HDTV cable box typically also controls and enables all the cool (but non-HDTV) digital cable functions that you probably want to use on your HDTV - things like Video on Demand and on-screen program guides.
Going boxless
Like many other electronic devices and services, digital cable (and HDTV cable) is going plug-and-play. So what's going on? Two main things are happening:
- TVs are being built as digital-cable-ready(DCR) - just as regular analog TVs have been built as cable-ready for analog cable for years. These DCR TVs have a QAM tuner built-in and a slot for a "smart card" called the CableCARD.
- Some cable companies rent these CableCARDs to their customers. A customer with a CableCARD and a DCR HDTV can simply plug the CableCARD into the HDTV - the card basically gives your TV "permission" to unscramble encrypted premium channels.
With this DCR HDTV and the CableCARD, you simply plug the cable into the back of your TV and you're ready to go.
