Coax Cable for TV Antenna: Everything Works Until It Does Not
Quick answer / TL;DR: Short answer: calculate the loss from antenna to outlet, counting cable loss, splitter loss and connector loss, and keep the result comfortably inside the receiver's tolerance. Use RG6 rather than RG59, terminate unused splitter ports, and keep the run as direct as possible. Where the margin is thin, improve the antenna or the cable before adding an amplifier.
Three coaxial families: BNC for CCTV, F-type for TV, N for RF – each with its impedance.Digital television has a threshold behaviour: above it the picture is perfect, below it there is nothing at all.
That makes a marginal installation indistinguishable from a broken one, and it makes the loss budget the only thing worth calculating.
This article covers the loss from antenna to television, the splitter arithmetic, and the cable and connector practice that preserves margin.
The receiver needs a minimum level to decode, and the installation either delivers more than that or it does not.
Cable loss rises with frequency, so a run that works for low channels may fail on high ones, which is why a single missing channel is a useful diagnostic.
The splitter is usually the largest single loss, and it is the element most often added without recalculating.
Loss Budget
| Element | Loss | Note |
|---|
| RG6 at 500 MHz | About 4 dB per 30 m | Rises with frequency |
| RG59 at 500 MHz | About 7 dB per 30 m | Avoid for long runs |
| Two-way splitter | 3.5 dB per output | Each output |
| Four-way splitter | 7 dB per output | Each output |
| Connector | 0.1 to 0.3 dB | Per joint |
| Wall plate | 0.5 dB or more | Cheap plates are lossy |
The wall plate row is easy to overlook. A plate with a poor internal connection can cost more than a metre of cable, and it is often the joint closest to the television.
Where a plate is used, choose one with a proper F connector rather than a push-on internal link.
Diagnosing by Symptom
All channels missing suggests the feed is disconnected or the antenna has failed.
High channels missing while low ones work suggests loss, because the highest frequencies suffer most.
One outlet worse than others suggests a splitter or a cable specific to that outlet, and swapping outputs at the splitter confirms it in a minute.
Intermittent loss that correlates with weather suggests a marginal level, moisture in a connector, or movement in the antenna.
Installation Practice
- Use RG6 with good shielding
- Terminate unused splitter ports
- Avoid daisy chained splitters
- Fit a proper wall plate
- Seal outdoor connectors against water
Real-World Applications
High channels fail while low ones work. The run is long and RG59, and replacing it with RG6 restores every channel.
One room has no signal. Its splitter output is faulty, and swapping outputs moves the fault with the port.
Reception fails after rain. Water has entered an outdoor connector, and replacing and sealing it resolves the fault.
A four-way split leaves every outlet marginal. A distribution amplifier at the split point raises all of them above threshold.
Standards and Verification
Coax loss is published per frequency by the cable manufacturer, and receiver tolerance is published in the television's specification.
Verification is a signal strength and quality reading at each outlet rather than a visual check of the picture.
Read the strength figure. A picture that looks fine may be one weather change away from disappearing.
Antenna and Amplifier Decisions
Before changing cable, confirm that the antenna is appropriate for the transmitters in use, since a mismatch of band costs more than a metre of cable.
Modern transmissions are often grouped in a narrower band than older wideband antennas cover, and a grouped antenna delivers more signal for the same size.
Where the antenna is adequate and the cable is adequate, an amplifier is the remaining option, and it belongs at the antenna rather than at the outlet.
An amplifier at the outlet amplifies the noise the cable has already collected, which does not improve the received signal to noise ratio.
Measure before amplifying, since a system that needs an amplifier at the outlet usually needs a cable replacement instead.
Record the signal readings at commissioning so that a later degradation can be identified against them.
A reading taken once, at installation, is the baseline that makes every future diagnosis faster.
Where readings are not available, the fastest diagnostic is to test the antenna directly at the first splitter with a short cable.
That single test separates an antenna problem from a distribution problem in a few minutes.
Distribution to Several Rooms
Feeding several rooms from one antenna requires a splitter and a loss budget that accounts for every outlet.
A distribution amplifier at the split point is the usual answer when the budget does not fit, and it must be placed before the split rather than at one outlet.
Where the cable runs are long, the highest-loss outlet defines the requirement for the whole system.
Balance the outlets so that the nearest is not overdriven while the furthest is marginal, using an attenuator on the short run where necessary.
Terminate every unused output, since an open port degrades the outputs that are used.
Record the splitter type and the amplifier gain so that a later outlet can be added without recalculating from scratch.
A room added later without a budget check is the usual cause of a system that was fine and then was not.
Check the furthest outlet after any addition, because that is where the shortfall appears first.
Related reading: Coax cable for HD antenna — blogs/news/coax-cable-for-hd-antenna
Related reading: Coax cable in-wall rating — blogs/news/coax-cable-in-wall-rating
Related reading: Coax cable signal loss — blogs/news/coax-cable-signal-loss
Frequently Asked Questions
Why do only high channels fail?
Cable loss rises with frequency, so the highest channels are the first to drop below threshold.
RG6 or RG59?
RG6 for any run of consequence. RG59 loses noticeably more.
How much does a splitter cost?
About 3.5 dB for two ways and 7 dB for four ways, per output.
Should I add an amplifier?
Only after checking cable and connectors. Improve the passive parts first.
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