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TV Coax Cables & Signal Loss


Twin-lead and coax Contents
1.) Cables
2.) Splitters
3.) Connectors
4.) Adapters/Baluns
5.) Loss Calculator


1.) CABLES

RG-6 coax cable
This cable is commonly used to connect a TV antenna to all television receivers. 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.

Twin-lead cable
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. Some twin lead cable does not weather well, degrades with time (more loss).

SUMMARY cable loss

Cable(1) Ohms(2) Shielding Primary Use
RG-6 75 2 - 4 Layers TV Reception
-- VHF / UHF
RG-11 75 2 or 4 Layers TV Transmission / Reception
-- High Power, Low Loss
-- VHF / UHF
RG-59 75 1 Layer Video Signals
-- can use for TV reception (VHF/UHF)
Twin-Lead 300 none VHF TV Reception
-- RF Channels 2 - 13

(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 characteristic impedance, the ratio of the electric to magnetic field.

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 (see The dB Scale).

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

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

RG Type & Frequency
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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2.) 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.

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.

Signal splitters (passive -- non amplified) can be used as signal combiners to connect multiple antennas. The Output and Input ports are reversed. The antennas are connected to the Outport Ports, the Input Port goes to the TV('s). Signal loss is the same for both directions. See Multiple TV Antenna Installation.

3.) 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 a female-to-female connector, also called a barrel. Wall jacks and coax ground blocks usually have barrel connections. Connectors introduce a small signal loss, typically about -0.5 dB.

4.) 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

5.) SYSTEM LOSS CALCULATOR

Estimate cables loss based on frequency and cable type and length, signal splitters, and connectors / 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 (barrels etc):
Adapters (300/75 ohm):

RF Channel
Frequency

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


TOTAL LOSS (dB)

Also see Booster / Distribution Amplifiers.

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