Difference between revisions of "DVB-S"

Revision as of 20:49, 26 December 2008

DVB-S Theory

DVB stands for Digital Video Broadcast - Satellite. At its core, DVB-S is a simple mechanism. Digital transmitters beam sets of channels to an area, and they are received by antennas aimed at the transmitter. The scope of this article is to provide basic understanding of DVB-S technology, dish pointing and peaking, and setup in MythTV. In keeping with the philosophy of the (largely US based) MythTV development and user community, no discussion of prohibited activities (civil or criminal) is welcome at any time. If some activity utilizing DVB-S is legal in your locale, bear in mind that it is likely *not* so in the United States (under whose laws MythTV must exist) and is therefore *still* unwelcome in all official MythTV support channels.

DVB-S and DVB-T (Digital Video Broadcast - Terrestrial) share in common many characteristics. They both share in common a remote transmitter broadcasting a signal through the air to an antenna, with bundles of channels (multiplexes) being transmitted by one or more transponders. In the case of terrestrial broadcasts, the need for precise aiming is less critical as the transmitters are largely omnidirectional and within short distances. In the case of satellite broadcasts, however, the antenna (dish) must be aimed at an object the size of a schoolbus at a distance of 35,000 kilometers. Precise aiming is, to say the least, critically important.

DVB-S satellites are in geosynchronous equatorial orbit. This means that they are in fixed orbital locations over a single spot on the equator. In populated portions of the world, there is a broadcast satellite at approximately every three orbital degrees. It is quite easily to mis-aim the dish slightly and get strong signal from the wrong satellite altogether.

Just as with terrestrial broadcasts, the quality and size of your antenna is directly proportional to the strength and type of signal being received. The two types of digital broadcast commonly in use today are C-Band and Ku-band. C-band is the older format of digital satellite broadcast, bringing to mind gigantic eyesore dishes. Ku-band is the format favored by consumer dish operators just as Freesat, DISH Network, and Bell ExpressVu. While it is possible to tune Ku and C-band signals with large dishes, only Ku-band signals can be tuned with the small round and elliptical "patio" dishes.

MythTV supports *only* unencrypted material, or material that is decrypted through the use of a legitimate provider-supplied CAM (Conditional Access Module). This rules our for-pay services that do not provide CAMs. Attempts to tune DISH network, DirecTV, Bell ExpressVu and similar are unwelcome in the MythTV community as those providers to no supply CAMs.

Equipment Needed

• DVB-S Tuner card
  • The DVB-S card must support the modulation and FEC (Forward Error Correction) used by the satellites you wish to tune. If the card does not support these specifications, you will be unable to une your channels! If your provider supplies CAMs, you will need a DVB-S card with an *on-board* (non-USB) CI slot, and the card and CI must be supported by linux.
• Satellite Antenna/Dish
  • The required size of the dish will be determined by the signals you wish to tune.
• One Low Noise Blocking Filter (LNB/LNBF) for each orbital location you wish to tune
• RG6 Coaxial cable
• Optional: A DiSEqC (Digital Satellite Equipment Control) Switch if using more than one Orbital Location/LNB

Equipment Setup

Dish Aiming

Dish Peaking

MythTV Setup