The 'Dark Fibre' Files: Cable TV Technology for Dummies

Posted by Sanchia de Souza at May 11, 2009 03:15 PM |
In the fourth entry documenting the making of 'Dark Fibre', a film by Jamie King and Peter Mann, Siddharth Chadha simplifies cable TV technology for the uninitiated.


Confused about the difference between an MSO and a COAX? Well, this will simplify cable TV for you.

The system of providing television to consumers using radio frequency signals transmitted to televisions using fixed optical fibers or co-axial cables is called cable television. This is different from the over-the-air method used in traditional television broadcasting (via radio waves) for which a television antenna is required. FM radio programming, high-speed internet, telephony, and similar non-television services may also be provided.

Still confused? It's simple.

Your local cablewallah is a Private Cable Operator, a private small cable company dealing/competing with the Multi System Operators (MSO), who is an operator of multiple cable systems. For example, Hathway, Siti Cable, In TV are MSOs who operate either directly or via small cablewallahs. When cable TV was first introduced in India, small entrepreneurs set up their private cable companies, providing anywhere between seven to twenty channels to their local neighborhoods. They put up their own cable dish to down-link the broadcast signals from the satellite. Up until 1997, this was the only way one could access cable television; but this changed with the entry of the Multi Service Operators, who used better technology to provide clearer pictures, better sound and up to a 100 channels.

The broadcaster up-links the signal to their channel via satellite. The MSO down-links this signal, using a control room or a rear end. Inside the control room would be a set of RF signal modulators. Scientific Atalanta is an industry standard in India that provides control room equipment to various MSOs. The MSOs, which started off with analog technology to transmit their signals, are now moving to digital cable, delivering cable television as digital data instead of an analog frequency.

Because many MSOs continue to use analog transmission for low-numbered channels, and digital transmission for higher channels, a typical digital cable box is also able to convert traditional analog cable signals. Despite the advance of cable-ready television sets, most users need a cable box to receive digital channels. However, customers who do not subscribe to any digital channels can go without; MSOs provide "basic cable" service within the analog range, avoiding the need for distributing a box. However, advanced carrier services such as pay per view and video on demand will require a box.

Digital television allows for a higher quality and quantity of cable TV signals. Digital transmission is compressed and allows a much greater capacity than analog signals it almost completely eliminates interference. Digital converters have the same purpose as analog ones but are able to receive digital cable signals. With more data than analog in the same bandwidth, the system delivers superior picture and sound quality.

The MSO further re-transmits the RF signal from to the cablewallah, via coaxial optical cables or simply known as COAX that in turn boosts this signal using amplifiers and provide it to various homes using a common type of optical cable called RG6. The term RG was initially used by the US Military as an abbreviation for Radio Guide, but the term is now obsolete. RG6, in common practice, refers to coaxial cables with an 18 AWG center conductor and 75 ohm characteristic impedance. It typically has a copper-coated steel center conductor and a combination aluminum foil/aluminum braid shield. They are usually fitted with F connector style, in each end.

Submariine Umblical Cable

Once the signal reaches a cablewallah, the responsibility of the MSO ends, and it is up to the Cable Operator to maintain and distribute cable television from there onwards. Once the signal reaches the consumer's home, it is processed by a television converter box, popularly known as a set top box. A set top box is an electronic tunning device that transposes or converts any of the available channels from a cable television service to an analog RF signal on a single channel. The device enables televisions which are not cable ready to receive cable channels.

Set Top Box

Modern set top boxes have a descrambling ability. The past three years have seen the entry of Direct to Home Pay TV operators, such as Tata Sky or Dish TV in the market, taking the technology to a new levels of sophistication, where the customers use a small cable dish to down-link the broadcasters signals which are processed with a set top box. In case of premium television, or paid channels, the broadcaster up-links an encrypted or a scrambled signal. When the signal reaches the home of the end user, it is reprocessed using a set top box, thus descrambling it and making it available for viewing on Television. A descrambler must be used with a cable converter box to be able to unencrypt all the premium and pay-per-view channels of a cable television system.


Now, put on that television, forget the tech and get back to the latest IPL match!

With inputs from MSOs, Local Cable Operators and Wikipedia for definitions of terms.