RG-6 coax (75 ohm) cables 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. Four layers has better immunity from interference, is more sturdy and durable (and expensive), but is less flexible than two layers. Quad shielded, 4 layers, should be used for outside cables.
RG-59 coax cable can be used, but it is a little more lossy and has only a single layer of shielding. Twin-lead (300 ohm) cable, sometimes called ribbon cable, is very lossy for UHF channels and should be replaced (with RG-6). RG-11 cable is designed for transmitting (higher power) over long cable runs, has less loss, is bigger and heavier, available with dual or quad shielding, and the most expensive.
|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|
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 (out/in) on a logarithmic (dB) scale.
-3 dB is about half, and +3 dB is about double.
|ratio||=||Pout / Pin|
Pout - power out of cable (watts)
Pin - power into cable (watts)
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.
(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 field.
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 an F-type female-to-female, also called barrel, cable connector. Wall jacks and coax ground blocks usually have barrel connectors. Cable 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 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.
Signal power in dBm drops directly by power decibels (dB) loss. The power unit "dBm" is decibels above or below one milliwatt (1 mW).
|Pout||-||signal power (dBm) out of cable.|
|Pin||-||signal power (dBm) into cable.|
A negative dBm is dB's below a milliwatt, a positive dBm is dB's above a milliwatt, 0 dBm = 1 mW. Television broadcast signals are typically between 10 kW (70 dBm) to 1000 kW (90 dBm). Receive signals are between -5 dBm (316 µW) to -65 dBm (0.0003 µW).
dBm = 10 log10 (mW)
mW = 10(dBm/10)
|dBm||- decibels above or below 1 mW|
|µW||- microwatts||=||0.000 001 W|
|mW||- milliwatts||=||0.001 W|
|W||- watts||=||1 W|
|kW||- kilowatts||=||1000 W|
TV Coax Cables, Splitters, and Connectors
|OTA DTv||© Copyright 2017|