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RF Cable and Satellite Tutorial

(Information compiled from internal and external sources. Wikipedia.org, etc.)

CATV - Community antenna television system. Offers the transmission of television signals, including those that originate at over-the-air broadcast stations, to customers on a wired network. CATV was the origin of the cable television networks known today.

Types of Splitters

Directional Couplers

Part Numbers: Directional couplers, or Taps as they are sometimes called, are used to extract a small portion of the signal from the distribution cable to feed subscribers taps, while maintaining the proper characteristic impedance of the ditribution cable. A directional coupler has three important parameters to check: insertion loss, isolation, and tap loss.

Tap Loss - The most important parameter of a directional coupler is the tap loss. Tap loss is how much lower the signal level at the tap output is, compared to the signal level at the input. Common tap loss values range from 3 dB to 28 dB. Directional couplers are placed at various locations throughout a distribution system based upon the required tap loss and signal level needed. If, for example, the signal level on a line is 28 dBm V, a directional coupler having a tap loss of 28 dB would be used to provide the signal of 0dBmV needed for a subscriber tap.

Insertion Loss - The insertion loss of a directional coupler should be quite small, typically about 1.5 dB.

Isolation - The isolation of a directional coupler becomes greater as the tap loss increases, with a typical isolation of 20 dB for a 3 dB directional coupler.

DC Voltage Blocking Coupler

DC Voltage Blocking Couplers (DC Blocks) are special connectors which have a capacitor (high pass filter) built into the device. These block DC on splitters and switches on coaxial lines.

LNBF - Low Noise Block Converter

Part Number: The LNB is located at the focal point (in the nose cone) of the satellite dish antenna and amplifies the very weak received satellite signal approximately 1000 times, then converts the received microwave satellite signal to a lower frequency so that not as much signal will be lost in the coaxial cable between the dish and the receiver.

There are two main types of LNBs. The most popular type is the LNB that is attached to a feedhorn and uses an external servo motor to turn a probe inside of the feedhorn to select the polarity of the desired channel. The other type of LNB is actually called an LNBF, where the LNB and feedhorn are one unit and the polarity is switched when the receiver changes the voltage (either 13 or 18 volts) going to the LNBF at the dish. Depending on what voltage is sent to the LNBF by the receiver, either the horizontal or vertical antenna probe inside the throat of the LNBF will be selected. LNBFs are also used on the smaller DBS satellite systems.

Amplifiers

Distribution Amplifiers

Part Numbers: A distribution amplifier is a type of amplifier that is mounted indoors, usually in a central location, and is used to "distribute" TV (or other) signals to multiple locations.

To determine whether or not you need a distribution amplifier, remove any signal splitters that may be connected to the TV antenna (or other source) and connect only one TV to the antenna. If the TV reception is good on this one TV, then reconnect the signal splitter(s) and check the reception on the other TV's.

If there is a noticeable reception difference between when the one TV was connected directly to the antenna and when the splitter was reconnected, then a distribution amplifier will probably be needed.

There are many different types of distribution amplifiers. Some are designed to amplify just off-air broadcast channels and others are designed to amplify off-air and cable channels. There are even some that have one, two and four output splitters built right into the amplifier.

Band Seperator Combiners

Part Numbers: Most combination or "all channel" VHF/UHF antennas have a connection for a single downlead, and in most locations a single high quality coax cable will deliver good VHF and UHF signals. However, a single downlead cannot be connected to both the VHF and UHF 300 ohm terminals on older TV's and VCR's. Instead, a VHF/UHF band separator with an input for coax is required. Connect the downlead coax cable to the input, and the two pairs of wires at the other end to the appropriate VHF and UHF terminals on the TV and/or VCR.

Signal Combiners

Part Numbers: Signal combiners are used to combine local off-air channels from a TV antenna with the modulated channel 3 or 4 signal output from a satellite receiver, VCR, DVD player or other audio/video device. This allows you watch any of the local channels from your TV antenna or the satellite channel from your satellite receiver on any TV in your house.

Inline Signal Amplifiers

Part Numbers: These amplify the signal the amounts stated on the different inline amplifiers. The inline amplifier is powered by the voltage already present on the satellite signal coax. Amplify the satellite signal before long runs and/or combining, splitting, or multi-switching.

Inline Signal Strength Attenuator Pads

Part Numbers: On shorter runs, many of the channels will be over amplified. Youíll know when this happens if the TVís audio buzzes when white printing is superimposed on the screen, i.e. car leasing details or a newscasterís name. To fix this problem, install some Signal Strength Attenuator Pads on the coax line at the television to knock down the level of the signal. Screw in-line with coax cable and reduce signal strength by rated amount. Try different combinations until you get the best picture quality. Use to balance signal strength from different sources.

TV - Satellite Diplexer / Mixer

Part Numbers: Satellite Diplexer / Mixers can combine a cable carrying VHF/UHF signals (from an antenna or CATV) with the cable from the satellite dish, or split a cable carrying both types of signals into their separate components. Looks and connects just like a regular splitter/combiner, but works with DSS signals!

Satellite Multiswitches

Parts: A multiswitch takes the input from both of the LNB's (both cables from a dual LNB dish HAVE to be connected to the multiswitch)...it then locks one of the LNB's to always look at the even transponders and the other LNB to always look at the odd transponders. This is why a multiswitch only works with Dual LNBs and not single LNB's. The switch then has multiple outputs to receivers (4,8,etc). When you connect the receiver to the multiswitch, the switch determines which of the two LNB's the receiver needs to look at depending if it needs to view odd or even transponders. When you change the channel, the switch then swaps your connection to the other LNB when needed. With a multiswitch, the LNB's never change which side they are looking at.

What is the 2x4, 2x8, 3x4, 3x8, 4x4, 4x8, 5x4 & 5x8 designations mean when referring to a multiswitch?
The first number is the number of inputs from the dish (or antenna) the switch has. The second number is the number of outputs the switch has.

A 5x8 multiswitch would handle 4 DTV inputs (Two Dual LNBs looking at the two satellites) and a Cable TV or antenna input if you wanted. It would have 8 outputs that could go to 8 DirectTV receivers, 4 Dual Tuner DirectTivos or any combo in between.

What is a cascadable multiswitch?
The receiver will send a 22khz tone to tell the multiswitch that it wants the 119 degree satellite. This tone is only used by the multiswitch and is not sent back up to the LNB's....if you have two 4xn switches connected or a 4xn multiswitch connected to the built in multiswitch on a dish, the "2nd" one will never tell the "1st" one that it needs to see the 119 so the receivers connected to the "2nd" one would ONLY see the 101 satellite.

There are switches designated as "cascadable" that WILL send that 22khz tone upstream, thereby allowing you to connect it in series with another multiswitch (such as a built in one on the dish).

How many inputs do I need on a multiswitch?
If you have an 18" dual LNB dish, you have 2 outputs from the dish, therefore only need a "2 x n" switch meaning 2 inputs from dish and "n" output (to be determined at next step.

If you have an Elliptical dish (or 2 18" dishes looking at different satellites), you will need a "4 x n" switch meaning 4 inputs (from dish) and "n" outputs.

You will also see switches listed as "3 x n" or "5 x n"...This just means that there is an extra input for Antenna or CableTV. These switches allow you to combine an Antenna/CableTV signal onto the same RG6 cables as your DirectTV signal and split it out at the TV end. This saves you valuable cabling issues since you will only have to run 1 cable to a receiver instead of 2 (or 2 cables instead of 3 in the case of DirectTiVos)

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