CH-6 CABLE TV

Cable TV Master antenna TV (MATV) CATV system is a cable sys. Closed circuit TV (CCTV)

Cable signal sources The first step is to collect the desired signal from available sources. Amplification and deliver to cable control room. Signal from various satellite is in UHF frequency in microwave spectrums So high gain antenna is required such as Horn type parabolic dish antenna

Cable TV System components- Dish antenna LNBC Multiplexer Attenuator Connectors Amplifiers Cables

1.Dish antenna The dish antenna are the microwave antenna which use a parabolic reflectors. Principle – The parabolic reflector collects all the electromagnetic waves from satellite. Due to parabolic shape reflected rays concentrate at focal point which gives the high gain signal.

Dish antenna can be a transmitter or receiver antenna. It is a transmitter antenna , then all the waves coming out of the source (which is at focus point) are reflected equally by reflector from every point.

If the dish antenna use as a receiver antenna, the construction remains same but at the focus point need to use a receiver instead of a source. The parabolic reflector will bring only those rays together which are coming in direction BA. These rays are brought together at the focus point. The rays arriving from any other direction are canceled out.

Specification Size – 8 feet Band- C(3.7 to 4.2 GHz) Focal length – 90cm Azimuth angle- 0 – 360o Gain- 36dB Properties – Ap = 6 (D/ʎ) 2 Ap= Directivity D=diameter of reflector ʎ = Wavelength

2.LNBC (Low Noise Block Conv.)

LNBC Main function of LNBC is to convert collected signal to a low frequency range to minimize losses in co-axial cable that carry dish antenna signals to control room. L.N.A – the composite signal collected by the feed horn is fed to a Low noise amplifier . LNA provides maximum gain, signal to noise ratio. Down converter – LNA output fed to a converter which converts the incoming microwave frequency (high frequency) into lower frequency. This is possible using local oscillator

BPF- Passes wanted I. F. signal from other signal. IF Amplifier- This signals are amplified by multistage I. F. Amplifier and then send to co-axial cable to the control room. Specification Input frequency – 3.6 to 4.2 GHz Output frequency – 950 – 1525MHz. Local Oscillator frequency – 5150MHz. Impedance – 75Ω

3. Multiplexer Multiplexer means many inputs gives only one output simultaneously. All signal added together Resultant output signal is a composite of all the channel signal.

Resistive summing network The combine Vo output which will appear across Ro is amplified by broadband distribution amplifier.

In cable distributor separated many channel to user by single cable Specification Input to output – 12 : 1 Frequency response – Flat upto 550MHz. Isolation – 35dB Need of Multiplexer In cable distributor separated many channel to user by single cable So, many input to one output. Types are- TDM,FDM

4. Attenuator Attenuator reduce signal strength by a specific value, expressed in dB. When input signal level is higher than Attenuated to correct value by Attenuated pad at he input of Trunk amplifier. To equalize the signal To mix the signal at different proportion Reduces distance by specific value witch is express in dB

5. Connector To make the connections between cable or to amplifiers . Use good quality of co-axial cable connector. Other wise loss of signal can done in reception side of TV. Advantages No loss of signal Easy to connect Soldering not required while connecting.

5. Connector

Two way connector- Two way splitters- splitting is done from having one input to two output. Three way connector- Three way splitters- splitting is done from having one input to three output.

6. Amplifier Amplifier increases strength of the input signal. Head End – the starting point for cable signals is called the Head End. Trunk Amplifier- amplified signal & fed into the trunk line. Types of amplifier used in cable TV distribution are- Trunk amplifier Bridge amplifier Line amplifier

Loses in cable are DC loss, Dielectric loss increase at higher frequency. 1] Trunk amplifier - Trunk amplifiers (20 or 30dB) are inserted at regular interval along with trunk route to reduces losses. 2]Bridge amplifier- act as bridge between the trunk line & branch line. Gain of amplifier is 20 or 30dB

3]Line amplifier – Branch lines are shorter in length, but they need amplifier of 20 or 30dB regular interval. Branch line is extended is called as line extender. Line extender amplifiers inserted in the branch line to reduces cable loss. Line extender extend no. of drop line.

7. Cable Co-axial cable Used in Wideband transmission line Two conductors separated by an insulator.

These types of Co-axial cable used for Trunk Line Hollow the inner conductor Larger cable diameter the less attenuator Trunk cable also made with waterproof jacket. RG-6Flexible coax used for cable drop lines Less loss at high frequencies. The cable diameter is (1/4) inch including the outer polyethylene jacket that makes the cable weather-proof.

Cables can be made of thin glass fiber. Minimum signal losses. Fiber optics – Cables can be made of thin glass fiber. Minimum signal losses. A modulated light beams signal introduces light into the glass fiber. Cable is lighter than copper conductor. It easier to install Loses are less Operated at high frequencies.