CABLE TELEVISION

Objectives:

1. Determining the modulator output attenuation before being distributed to customers. 2. Determine the amount of attenuation along the channel. 3. Knowing the strengthening of the cable television amplifier

Equipment Used:

1  Spectrum Analyzer

1  Modulator 3 kanal

2  Connector matching impedance 75 W

2  Television

2  VCD player

1  Connector Cable 75 W (± 2 m)

1  Coaxial Cable RG-59 75 W (± 140 m)

1  Connector N male to BNC female
 Circuit Diagram :

D. Preliminary Compiler Components CATV Network

a. Headend

Headend is the source of the emitted signal to cable systems. Headend not only receive local broadcast signals to be transmitted, but also can receive signals: broadcast from a distant city, broadcasts from satellites, and from wave microwave. Therefore, the headend is equipped with supporting devices, such as towers and various types of antennas, including satellite dish, to receive broadcasts from satellites. In addition, the headend may have broadcast their own programs and thus require an adequate studio to produce a broadcast program. For this application, the headend can set their own time and channel is required. As for time and channel for community access is usually entrusted to the local franchise. In general, cable TV systems can not do the editing control over the quality or content of community access programs. Cable system consists of two parts, the trunk system and distribution system. Trunk system works to send signals to groups of customers. The devices in the system and the trunk is a trunk cable trunk amplifier. Trunk amplifiers serve to strengthen the signal is weakened due to the length of cable. He was installed at each distance. Total amplifier mounted on the cable is limited by the noise and distortion on the amplifier in question. Good quality cable will reduce the number of amplifiers to the same cable length. Functioning distribution system to distribute signals to each home in one group of customers. Between the trunk and distribution system installed interface called Bridger amplifier. Support device distribution system is distribution cable, line extender amplifiers, and taps. The function of line extender amplifiers in the distribution system similar to the function of trunk amplifiers in the trunk system. TAP serves as a point of decision or branching signal to the drop cables associated with the device on the customer. Unlike the rigid structure of distribution cable, drop cable has a flexible structure / flex.

The main function of the headend include: • The source of all the agenda of the program. • Place of processing and penyambungansinyal from various sources. • Place of processing and administering the event. 
b. Modulator and demodulator

Source signals received by the headend device will be modulated to a certain carrier frequency before being sent to the combiner. Therefore, dibutuhkanperangkat modulator capable of laying menempatkanatau source signals at the appropriate RF carrier signal. Demodulator is used to separate the signals from the baseband audio and video frequency carrier signal. 
c. Coaxial cable

Coaxial cable serves as liaison throughout both active and passive components on a network of coaxial and collectively - the same transmit RF signals to the customer.

a. Express and Feeder Cables

Large diameter coaxial cable is used to transmit signals at a considerable distance. While coaxial cable with a smaller diameter is used to transmit signals in close proximity. In addition, when the amount of loss that is caused by higher losses than the losses tap the cable it self.

b. Kabel Drop and In-home

Drop cable and in-home coaxial cables commonly used with copper plated steel center conductor (copperplated steel). In a general cable system, nearly half of the total length of cable used by cable drop.

c. Amplifier Amplifier is an active device that serves to strengthen the RF signal so that it remains at the level desired.

d. Splitter

Splitter is a passive device yangberfungsi to split the signal. The use of splitters due to the limited number of output and an active devices (amplifiers), so that with the use of coaxial cable splitter arahpenggelaran into consumers' homes may be reproduced.

e. Directional Coupler

Directional coupler is a passive device that serves as pencabang the coaxial network. The working principle of the directional coupler is almost identical with the splitter, namely the division of the input signal.

f. Tap

Tap is a passive device that serves as a point of final termination of the coaxial network before they were distributed to the homes of customers.

g. Terminator
Terminator a device that functions as impedance matching or closing channels that are not used by the user.  
Distribution Cables Frequency losses in coaxial cables is high, especially those working in the super frequency region from cable TV. However, loss-loss of channel offset by using a radio frequency amplifier (RF amplifier) with a wide field of frequencies that are placed along the cable network as shown. In distribution systems, main channel is the trunk. From this main line, branch cables extended to groups of customers. Channel for each customer referred to the drop. Each amplifier channel has a strengthening of the same trunk with a loss channel for the distance between the amplifier. Typical value is 40 dB, or a strengthening of the voltage at 100.

Experimental Procedure

Prior to testing, calibration done prior to the Spectrum Analyzer. After that test the modulator output can be started 

Note:  For each test, before being connected to the Spectrum Analyzer will be better used than 75 W impedance matched to 50 W (attenuation 7.8 dB).

For each measurement of TP, do not connect the entire system to be measured. For example, measurements TP1 just installed only the modulator, modulator and cable TP2 just roll it, and so on.

• Measure and image frequency spectrum at the measurement point (TP1) to see the modulator output signal level on each channel. The cable used in this test form koaxial cable 75 W (± 2 m), with block diagram as shown below. 
  

• Repeat the test using a long cable (± 150 m) is TP2, with block diagram as shown below. Image of the frequency spectrum and determine the level. How many dB attenuation that occurred on the cable.
  

• Repeat testing for TP3, TP4, TP5, TP6, and TP7 as in steps 1 and 2. Determine the strengthening of the amplifier, the cable attenuation, attenuation at each port splitter.  
  
• Repeat to TP 2 and TP 4 with moving the cable roll.
  

  
   

  The experiment results
  

   
   

  
  

  
   

  
  

  
  

  
  

   
  Data Analysis
  
  
  Coaxial cable used in cable distribution system for cable wrapping and taking minimize radiation interference signal. Impedance which is owned by an infinite length of cable is Z0. Ending a sluran in his Zo generate maximum power transfer to the load. In the cable channel does not have standing waves and reflections. Zo standard in television is 75 Ω.
  

Attenuation in the cable signal generated by I²R losses and the effect of surface (skin effect) and by losses in electrically conductive. Loss - loss of roots increased frequency and higher tempratur.

To replace the losses in the channel amplifier is used, including parent amplifier, bridge amplifier, the amplifier channel.Standard level for the signal at the receiver cable television signal is 3 mV.

Cable attenuation at the first roll of the CH1 = 16.8 dB; CH2 = 6.17; CH3 = 20.4 dB, while weakening that occurred on the second roll cable for the CH1 = 21 dB; CH2 = 21 dB; CH3 = 20 dB attenuation differences that occur in both one of these cables due to cable cuts or rolls have shorter, is said to be shorter if the slowdown is happening smaller so that experienced cuts cable is a cable roll. The strengthening of this experiment is obtained about 20 dB, which is strengthening CH1 = 17.8 dB; CH2 = 17.6 dB; CH3 = 20 dB. The weakening of the splitter around 7-8 dB

Conclusion 

• Loss will be a big loss in the channel when the channel is not matched with radip frequency amplifier (RF amplifier) that remain at the desired level.
  
• The amount of attenuation along the canal about 48 dB attenuation is obtained from the sum of all the good that happened along the channel on the cable roll 1, roll 2 cable, and the splitter. 
  
• Attenuation that occurs in both the cable roll 1 and roll 2 rolls around 16-21 dB