EXPERIMENT 4 CABLE TELEVISION

PURPOSE

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.

Used Equipment

1. A Spectrum Analyzer 
2. 1 Modulator channel 3 
3. Connector 75 Ohm impedance matching 
4. 2 Television 
5. 2 VCD player 
6. A connecting cable 75 Ohm ( 2 m) 
7. An RG-59 coaxial cable 75 Ohm (140 m) 
8. Connector N male to BNC female

Circuit diagram

INTRODUCTION

 
Edge Head (Head End)

Edge provides event signals (programs) for all channels. Local broadcasting and a much captured by an antenna mounted on top of a very high tower in order to extend the distance limit of view. These signals can be distributed it as their home channel number or frequencies diheterodinkan into different channels.

 

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 Figure 2.3.
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 if used matching impedance of 75Ohm to 50 Ohm (7.8 dB attenuation).
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.

1. Measure and draw the 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 Ohm  ( 2 m), with block diagram as shown below.

 

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

3. Repeating the test to TP3, TP4, TP5, TP6, and TP7 as in steps 1 and 2.Determining the strengthening of the amplifier, the cable attenuation, attenuation at each port splitter. 

4. Repeating for TP 2 and TP 4 with moving the cable roll.

   Experimental Results

TP1              REF=80dBµ      CF=2MHz            50MHz/DIV BW=1MHz      CP1∆F+92MHz    ∆V+16.8dB  Amplitudo Sinyal = 80dBµ	TP2 REF=80dBµ    CF=4MHz          50MHz/DIV BW=1Mhz    CP1∆F+92MHz  ∆V+17,6dB Amplitudo Sinyal = 62dBµ
TP3 REF=80dBµ      CF=4MHz            50MHz/DIV BW=100KHz      CP1∆F-5.36MHz    ∆V+80dB Amplitudo Sinyal = 73dBµ	TP4   REF=60dBµ      CF=13MHz          50MHz/DIV BW=100KHz      CP1∆F-5.84MHz  ∆V+6.4dB Amplitudo Sinyal = 40dBµ
TP5 REF=60dBµ       CF=12MHz            50MHz/DIV BW=100KHz      CP1∆F-5.92MHz    ∆V+4.4dB Amplitudo Sinyal = 30dBµ

 

 

Data Analysis
 

DiliharTP1, TP2 and TP3 loss frequency is very large. While at TP4 and TP5 small. This is because at TP4 and TP5 already dimbangi channel using radio frequency amplifier (RF amplifier).

Conclusion
 
Loss will be a big loss in the channel when the channel is not matched with radip frequency amplifier (RF amplifier).