RG-6 coax cable
This cable is commonly used to connect a TV antenna to all televisions and devices. RG-6 is available with 2, 3, or 4 layers of shielding. Three or four layers has better immunity from interference and is more sturdy and durable, but is a little more expensive and less flexible than dual shield. Quad shield should be used for all outside cables.
RG-11 coax cable
This cable can be used if signal loss is a problem, usually long cable runs. The advantages of RG-11 cable are it has the least loss, and is available with dual or quad shielding. The disadvantages are it's more expensive, bigger and heavier. This cable is primarily designed for low loss and high power transmissions.
RG-59 coax cable
This cable can be used, but is more lossy and has only a single layer of shielding. RG-59 is usually used indoor's for raw video signals (recorders, games, etc.). RG-59 was used for OTA Tv and cable TV before RG-6 became common.
This cable is sometimes called flat or ribbon cable, and should be replaced. Twin-lead works well for VHF frequencies and is great for VHF-Lo channels, but is very lossy for UHF channels and has no shielding.
|RG-6||75||2 - 4 Layers||TV reception|
|RG-11||75||2 or 4 Layers||TV - High Power, Low Loss|
|RG-59||75||1 Layer||Video Signals|
(1) RG stands for "Radio Guide", and is widely used to describe cable performance. RG designations were developed by the military during World War II. The military has replaced the radio guide reference with military specification MIL-C-17.
(2) Ohms is cable impedance, the ratio of the electric to magnetic fields.
The longer the cable the greater the signal loss. Loss also depends on frequency, the higher the frequency (the higher the RF channel), the greater the loss. RF channels in the VHF band have less loss than channels in the UHF band. Cable (signal) loss is measured in power decibels (dB), and is the power ratio (watts out / watts in) on a logarithmic (dB) scale (see The dB Scale).
Cable loss depends on length, coax type and frequency (RF channel).
Note, loss calculations are for high quality cables. Cheaper cables may have greater loss, and may not weather well. Some higher quality cables may have less loss. Differences can be as great as plus or minus several dB per 100 feet.
A signal splitter / combiner is used to connect to multiple TV's and devices. Splitting the signal to 2 output ports delivers a little less than half the signal to each output. Signals at the outports are reduced by -4 dB, equivalent to adding about 70 feet of cable. The more outport ports, the greater the signal loss. Keep the number of signal splitters to a minimum.
Splitter and wall output ports that are not used should be terminated with a 75 ohm load or terminator.
Cables and most televisions and antennas use F-type connectors, male connectors on the cable, and female connectors on the antenna and television. Two cables can be connected using a female-to-female, also called barrel, cable connector. Wall jacks and coax ground blocks usually have barrel connections. Connectors introduce a small signal loss, typically about -0.5 dB.
ADAPTERS / BALUNS
Older antennas and TV's use a 300 ohm twin-lead connection, in these cases a coax-to-twin-lead adapter (75/300 ohm) is required. The adapter is a matching network (discrete and/or strip-line resistors, capacitors, inductors) or a balun (matching ferrite transformer). An adapter works both ways (bi-directional), signals go from coax to twin-lead or twin-lead to coax.
300 / 75 OHM ADAPTER LOSS
-0.2 dB for channel 2
-1 dB for channel 14
-2 dB for channel 69
SYSTEM LOSS CALCULATOR
Estimate cable system loss based on frequency and cable type and length, signal splitters, and connectors / adapters.
Also see Booster / Distribution Amplifiers.
Over-the-Air Digital TV (OTA DTv)
TV Coax Cable Systems and Signal Loss
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