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TV Coax Cable Systems and Signal Loss


Contents -- Cables | Splitters | Connectors | Adapters/Baluns | Loss Calculator

Twin-lead and coax CABLES
RG-6 coax (75 ohm) cable with F-type male connectors should be used to connect the 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 more a little more expensive and less flexible than dual shielded. Quad shielded should be used for all outside cables.

RG-11 coax 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 can be used, but it is a more lossy and has only a single layer of shielding. This cable is usually used indoor's for raw video signals (recorders, games, etc.)

Twin-lead (300 ohm) cable, sometimes called ribbon cable, should be replaced. Twin-lead is great for VHF-Lo channels, but is very lossy for UHF channels and has no shielding.

cable loss
Cable(1) Ohms(2) Shielding Use
RG-6 75 2 - 4 Layers TV signals
RG-59 75 1 Layer Lower Frequency, Video
RG-11 75 2 or 4 Layers High Power, Low Loss
Twin-Lead 300 none VHF and lower

(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.

Signal Loss
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.

Cable loss depends on coax type and frequency (RF channel).

Cable Loss Calculator
Cable Type:
RF Band or Channel:
Cable Length(s):

Cable Loss in decibels (dB)

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.

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SIGNAL SPLITTERS
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.

Signal Splitter Loss - -
Output
Ports
Loss
per Port
2 -4 dB
3 -6 dB
4 -8 dB
8 -12 dB

Splitter and wall output ports that are not used should be terminated with a 75 ohm load or terminator.

CONNECTORS
Barrel Connector Male-to-Male Connector Male-to-Female Connector 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 an F-type 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. Adapter

300 / 75 OHM ADAPTER LOSS
-0.2 dB for channel 2
-1 dB for channel 14
-2 dB for channel 69

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SYSTEM LOSS CALCULATOR

Estimate signal loss for the TV (outlet or outlets) with the most splitters and longest cables to the antenna. Trace the signal from the antenna to the TV, noting cable length, and the number and type of signal splitters, and the number of connectors and adapters.

Antenna-to-TV Signal Loss
Cable Type:
RF Band or Channel
Cable Lengths(s):
Signal Splitters: 2 Ports , 3 Ports
4 Ports , 8 Ports
Connectors:
Adapters: 300 / 75 ohm

Cable Loss (dB)
Splitters Loss (dB)
Connector Loss (dB)
Adapter Loss (dB)


TOTAL LOSS (dB)


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TV Coax Cable Systems and Signal Loss
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