RG6 should be used exclusively for satellite hookups and digital CATV. RG59 is fine for analog CATV signals but will not support the higher bandwidth used for satellite signals.
When should I use RG59 versus RG6? First let's discuss what RG means and what do the numbers stand for. All of the common RG designations apply to various types of coaxial cable. Coaxial cable is a general classification. Any cable that has two conductors which share a single common axis is a coaxial cable. This cable has a center conductor, along with a shield, the dielectric keeping the two apart, and an outer jacket wrapping. All common video cables are coaxial cables, though sometimes it may be harder to tell this than at others. An example is an s-video cable, which is usually two mini-coaxial cables in either a zip-cord arrangement, or a common jacket.
The RG designation originated in old, long forgotten military specifications; RG stood for Radio Guide and the numbers are almost completely random. Most of the cables today are called RG-# “type”, which means that they do not strictly conform to the specifications of the original Radio Guide.
Coaxial cable is the usual means of transferring video signals from one piece of equipment to another. Coaxial cable may be called simply "coax". Coaxial cable is the most commonly used cable, but also the least costly, most convenient, most reliable, and the easiest to maintain, in the way of transferring electronic images in a CCTV system. Coaxial cable is available from numerous manufacturers and comes in a large variety of shapes, colors, sizes, capabilities and specifications. The coaxial cable type that is the most commonly recommended is RG59/U, but this standard really represents a cable family with largely differing electrical characteristics. Other varieties that are like RG59/U are RG6/U and RG11/U. These varieties are used mainly in video work and CCTV. Though each cable group is similar in many ways, each group has its own electrical and physical characteristics, which must be considered. All three coaxial cable groups are included in the same general family classification for coaxial cables. The RG reference is the cable specification for use as a "radio guide ", while the numerical value helps differentiate the specifications of each individual cable. Although each cable has its own number, characteristics, and size, there is no difference in the way these different numbered cables work.
RG6 Dual or Quad Shield shouldn't be utilized for base band applications, such as video projectors, component video, plasma TV’s, etc. It may sound like a great solution because of all the layers of shielding, but RG6 Dual and Quad Shield don't have the proper type of shielding for the above described applications. It is manufactured using foil shields and braided aluminum shields. The makeup of the shields differs between models. The effective range of operation for foil shields is above 50MHz, which makes them perfect for rejection of radio frequency interference, or RFI, that may have an effect on satellite or cable installations. At frequencies below 50 MHz, however, foil shields are not effective. The braiding on the RG6 Dual shield and the RG6 Quad shield doesn't have enough coverage to work effectively with baseband applications.
The frequencies that are used in High Definition are usually around 37 MHz. For those lower frequencies, an RG59 with an 95% copper all-copper shield is designed to block RFI inclusion at base band frequencies. RG59’s “big brother” is an RG6 Single Shield , which consists of the same makeup as RG59 but has a thicker center conductor, for less signal loss, and longer runs. Because RG59 does not have a foil shield, it shouldn't be utilized for satellite feeds or cable feeds.
RG59 has a little less signal reduction, or attenuation, over 100 feet. The shielding on RG59 does not work quite as well to maintain Gigahertz level signals inside of the center conductor. RG6 has a better design for maintaining the signal levels inside the center conductor. This is the reason RG6 has become the standard for broadband CATV and satellite systems. A basic rule of thumb is to use RG6 for any Rapid Frequencies, and use RG59 for video frequencies. RG6 has an aluminum braid and an aluminum shield. RG59 comes with a copper braid, and in some instances, an aluminum braid and shield, although this is quite rare.
For any broadband CATV or satellite system, RG6 is recommended by all the experts. For any signals that are video frequencies RG 59 will be adequate but RG6 could be used as well.