TV Antenna Signal Distribution, Splitters and Multiple TV's

Yes. One properly designed TV antenna system can provide Over the Air television signals to multiple televisions, DVRs, tuners, or other compatible receivers.

A passive splitter is commonly used to divide the antenna signal between multiple coaxial cable runs. Each television then has its own tuner and can independently watch any channel being received by the antenna system.

The important consideration is that splitting an RF signal introduces signal loss. The signal available from the antenna is divided among the splitter outputs, and the splitter itself also has a small amount of additional insertion loss.

A two way splitter typically introduces approximately 3.5 to 4 dB of loss on each output. A four way splitter commonly has approximately 7 to 8 dB of loss per output. Actual specifications vary by splitter and frequency.

This means that an antenna system working reliably on one television may become marginal after the signal is divided among several televisions.

The correct solution is not necessarily a larger antenna or amplifier. First determine how much signal is available, then account for the losses between the antenna and each television.

Every passive splitter introduces insertion loss, which is the reduction in RF signal level between the splitter input and each output.

Even an ideal two way splitter must divide the available RF power between two outputs. Dividing the power equally results in approximately 3 dB of theoretical loss at each output. A real splitter also has internal losses, so an actual two way splitter commonly measures approximately 3.5 to 4 dB of insertion loss per output.

The same principle applies as the number of outputs increases. Typical values are approximately:

2 Way splitter: 3.5 to 4 dB loss per output.

3 Way splitter: 3.5 to 7.5 dB loss per output, depending on output.

4 Way splitter: 7 to 8 dB loss per output.

8 Way splitter: 10.5 to 12 dB loss per output.

Always use the insertion loss printed on the splitter or listed in its specifications when designing a system because actual values vary.

A 3 dB reduction represents approximately half of the RF power. A 6 dB reduction represents approximately one quarter of the original power.

This does not mean that adding a splitter automatically causes reception problems. If the signal arriving at the splitter has adequate margin, the television can continue receiving the channel reliably after the loss.

Problems occur when the additional splitter loss pushes a marginal channel below the tuner's reliable decoding threshold.

Most passive components between the antenna and television introduce some amount of attenuation or insertion loss.

This includes:

Coaxial cable

Splitters

Combiners

Filters

Diplexers

Grounding blocks

Connectors

Adapters

Wall plates

Couplers

Other passive RF components

A properly installed F-connector or high quality grounding block should introduce very little loss, while a splitter or long coaxial cable run can introduce substantially more.

Losses are cumulative.

For example, if a signal passes through 100 feet of coaxial cable that introduces 5 dB of loss, followed by a splitter with 4 dB of insertion loss, the total distribution loss is approximately:

5 dB + 4 dB = 9 dB

Additional components would add additional loss.

This is why a TV antenna system should be considered from the antenna all the way to the tuner. A station can arrive at the antenna with adequate signal strength but become too weak after passing through a poorly designed distribution network.

An amplifier is different because it is an active component. Instead of attenuating the signal, an amplifier adds RF gain. That gain can be incorporated into the same system calculation.

A TV antenna distribution system can be designed using an RF gain and loss budget.

The basic concept is straightforward:

Start with the signal level received by the antenna, add antenna and amplifier gain where applicable, then subtract every distribution loss between the antenna and each television.

For example, assume a desired station produces a signal level of:

-55 dBm at the antenna

The antenna provides:

+8 dB of realized gain

The resulting level would be approximately:

-47 dBm

A preamplifier then provides:

+16 dB gain

The signal leaving the preamplifier would be approximately:

-31 dBm

Now assume the distribution path to one television contains:

100 feet of coax = -5 dB

4 way splitter = -7.5 dB

Additional passive components = -1 dB

The estimated signal arriving at that television would be:

-31 - 5 - 7.5 - 1 = -44.5 dBm

That provides a much more useful understanding of the system than simply asking whether an amplifier or splitter is being used.

The calculation should be performed for the weakest important channels and for the longest or highest loss distribution paths.

It is also important to remember that signal level alone does not guarantee reception. Signal quality, signal to noise ratio, interference, multipath, amplifier noise, and overload can also affect whether the tuner successfully decodes the signal.

The objective is therefore not to produce the highest possible signal level. The objective is to provide adequate signal level and signal quality with sufficient operating margin at every receiver.

A professional RF signal meter provides the best starting point because it allows the actual signal levels at the installed antenna to be measured.

However, a useful preliminary system design can still be created without a meter by using predicted signal levels for the installation address.

The Channel Master TV Antenna Map & Technical Information Tool provides location specific information about available stations, including RF channels, tower directions, distances, frequencies, and predicted signal strengths.

Channel Master TV Antenna Map & Technical Information Tool

These predictions can be used as a starting point when the antenna is installed outdoors, appropriately selected for the required frequencies, mounted at a suitable height, and properly aimed toward the desired towers.

Once an estimated starting signal level is established, the distribution system can be modeled by adding expected antenna and amplifier gain and subtracting coaxial cable, splitter, and other passive losses.

For example:

Predicted signal level

+ Antenna gain

+ Preamplifier gain

- Coaxial cable loss

- Splitter loss

- Filter and other passive component losses

= Estimated signal level at the television

This calculation can be performed separately for each important station and each receiver location.

Predicted signal levels should still be treated as estimates, not measurements. Buildings, trees, terrain, antenna height, reflections, interference, installation location, and other local conditions can cause the actual signal at the antenna to differ from the prediction.

For a large, commercial, difficult, or marginal installation, measuring the completed system with appropriate RF test equipment remains preferable.

Coaxial cable performs two important functions in a TV antenna system. It carries the desired RF signals while also shielding those signals from the surrounding RF environment.

Two important specifications are therefore attenuation and shielding effectiveness.

Attenuation describes how much signal is lost as it travels through the cable. Cable loss increases with length and generally increases as frequency increases.

For example, the same 100 foot coaxial cable run will normally have more attenuation at a high UHF frequency than at a Low VHF frequency.

This is why coaxial cable specifications commonly list attenuation in dB per 100 feet at several different frequencies.

Shielding helps prevent unwanted RF signals and electrical noise from entering the cable and helps prevent signals inside the cable from leaking out.

High quality RG6 coaxial cable with effective shielding is generally recommended for modern TV antenna installations. Channel Master recommends high quality RG6, particularly for outdoor installations and systems where maintaining signal integrity is important.

Cable construction also matters physically. Poor quality cable may use inferior shielding, center conductors, jackets, or materials that deteriorate more quickly outdoors.

Even high quality coax can perform poorly if it is crushed, sharply bent, damaged by fasteners, improperly terminated, or exposed to water through an improperly weatherproofed connection.

For a reliable distribution system, cable should therefore be evaluated as an RF component rather than simply as wire connecting the antenna to the television.