Understanding the Performance
RG-6 Coaxial Cables
3.2001
Are there differences?
Is there really a difference between one RG-6 and another? Why should I buy
a cable for $0.60/ft when I can get one for $0.09/ft.Should I buy quad-shielded cable instead of dual or single-shielded? I’ve heard terms like VP, bandwidth, and capacitance used when describing coax cables.What do these
terms mean? Do the materials used to construct the cable really effect the
performance,and are they worth the extra cost?
shielding- The shielding is what protects the signal from outside
interference such as EMI and RFI, while also providing a return for
the negative signal back to the source.So, shield materials can
have a large effect on performance.
There are just a few determining factors when it comes to coaxial cable
design. But if the proper specifications are not followed, the performance of
the cable will suffer. Here is some background technology information on
those determining factors and how they effect performance:
dual-shield vs. quad-shield— It’s really not the number of shields,
but how well they cover that really matters. Coverage, and resistance is everything when we consider shielding.The rule is at least
95% coverage copper braid (for low frequency protection) and at
least 20° to 30° overlap on the foil shield (for high-frequency protection). Shielding is not cumulative,two braided shields that are
60% and 40% coverage will not give you 100% coverage,the combination can actually only end up to be about 80%,leaving 20%
uncovered.Also,more is not necessarily better. Anything more than
100% shielding can be overkill just creating more capacitance,
which reduces the bandwidth of the cable,and in turn system performance. Quite often, quad-shielded cables will tend to increase
capacitance to such high levels,they will actually reduce the systems overall performance. So,in most cases, a well designed dualshielded cable will work best.This is why most manufacturers top
level cables are dual-shielded.
conductors- Copper is the best choice due to its high conductivity, affordability and workability. The purer the better, with the standard at, at least 99.99%
pure.In less expensive cables, copper-clad steel is often used. Steel cables
are undesirable due to the increased resistance/impedance created by the
steel conductor. Silver is often used,in some more expensive “upgrade”
cables (due to its very low resistance/impedance at higher frequencies),but
the cost can be prohibitive. For high performance,high bandwidth systems, a
great alternative to solid silver is silver-clad copper which provides excellent
performance at a fraction of the price of pure silver.
dielectric material- The primary dielectric is the insulating material
that separates the center conductor from the shield. The more air in
the dielectric material, the lower the capacitance, and the higher the
velocity of propagation (VP). Foamed or gas-injected dielectrics are
more costly to manufacture, but are necessary for low capacitance
and high velocity of propagation. VP is the speed that the signal travels through the wire and its value is expressed as a percentage of
the speed of light. Low capacitance and high velocity of propagation
are key for wide bandwidth high-quality video transmission.
the differences– All cables are not created equal.The better the materials,
construction techniques and technology—the better the performance.
Understanding this is extremely critical,since you can’t easily upgrade your
cable once it’s in the wall. Make sure you get it right the first time,install a
cable that provides the best performance.Wiring with the correct product will
ensure all of the performance possible and will not limit future system
upgrades.This is especially true, once you consider the extreme bandwidth
demands of modern High-Definition and Digital TV signals.
Below is a comparison of various cables and their construction.
a comparison of various brands and models of RG-6 & RG-59 coaxial cables
brand
model
VP
Capacitance
Conductor
Monster Cable
Shielding
Dielectric
94% Copper braid/Aluminum foil
foamed Polyethylene
60% Al braid/Al foil (5° overlap)
foamed Polyethylene
dual
Monster Satellite
74%
67pf/m
Copper (OFC)
Coleman
dual
E100316 HDVT
78%
57.2pf/m
Copper
Commscope/Liberty
dual
C5775
76%
61pf/m
Copper-Clad steel
60% Al braid/Al foil (10° overlap)
Belden
foamed Polyethylene
dual
Brilliance 8281B
66%
68.9pf/m
Copper
98% dual Cu braid/no foil
MIT
foamed Polyethylene
dual
OneWire RG-6 Silver
83%
52pf/m
Silver-Clad Copper
97% Cu braid/Al foil (30° overlap)
Gas-injected PE
OneWire RG-59 Silver
82%
55pf/m
Silver-Clad Copper
95% Cu braid/Al foil (20° overlap)
Gas-injected PE
(Cu=copper, Al=aluminum)
(PE= Polyethylene)
Summary:
The MIT OneWire cables are two of the very few coaxial cables available on the market today that are truly ready to handle the extreme
bandwidth demands of modern High-Definition and Digital TV signals.These high performance double shielded (95-97% tinned-copper
braid over 20-30° overlap aluminum foil) cables feature silver-clad and oxygen free copper (OFC) conductors and a gas-injected dielectric that provide very low capacitance, extremely wide bandwidth and a extremely high (83%) velocity of propagation.
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