EXPERIMENT II (VIDEO MODULATOR)

Objectives:
1.Measuring the frequency spectrum of video transmission.

2.Determine the image carrier frequency range and sound carrier frequency.

3.Specifies the bandwidth on video transmission.

4.Specify the type of modulation on the picture and sound

Equipment Used:

1 Video modulator (VCD / VTR / video sender).

1 Spectrum Analyzer.

1 cable connector RCA- BNC.

Circuit diagram:

Introduction:

How to transmit image signal which the amplitude is modulated similar to a radio broadcasting system that has been known.
In both cases, the amplitude of a carrier wave radio frequency (RF) is made varies with the modulating voltage. The modulation is a signal of fundamental frequency (baseband).
On television, this baseband signal is a composite video signal. Television broadcast is similar to a radio system, but includes pictures and sound.
Sound signal emitted by joining it in frequency modulation (FM) on a separate carrier wave transmitter in the same channel as the image signal.

This image signal means a modulated carrier wave.
The video signal is a signal for a picture tube. Video signal for the television audio is correspond to the sound system signal. Details for the AM image signal (amplitude modulation picture) and an FM voice signal.

Figure 2.a shows the frequency spectrum of video transmission that produces an image signal comprising AM picture carrier frequency (center frequency) and sound carrier frequencies (frequency side of the upper and lower side frequencies) - without VSB, while Figure 2b shows the frequency spectrum in transmission generate video image signals of AM frequencies only have the upper side only (with VSB).

Experimental Procedure:

1.Calibrate the Spectrum Analyzer by determine the reference spectrum.

2.Set-up instruments just like in the picture above.

3.Turn ON the instrument.

4.Measure the video modulator output (RF) using the Spectrum Analyzer and observe the frequency spectrum.

5.Draw the frequency spectrum.

6.Determine how much is the images carrier frequency, voice carrier frequency, and the difference between.

7.Amati spektrumnya, menentukan jenis modulasi yang dipergunakan pada transmisi tersebut, dengan cara mengubah FREQ.Observe the spectrum, determine the type of modulation used in transmission by changing the SPAN FREQ (reduce the scale).

8. Draw the multiples frequency spectrum from it's frequency base.

Question:

1.What system is used in the video modulator?

2.From step 6, how do we know what types of modulation?

Experimental results:

Image of Frequency Spectrum	Information
	Ref = 102dBμ BW = 100 KHz CF = 5 MHz CP1ΔF + 4.32 MHz 2 MHz / DIV ΔV + 18.8 dB Image Carrier Frequency: LSB = 5 MHz - 4.32 MHz USB = 5 MHz + 4.32 MHz Voice carrier frequency: can not be detected by the frequency spectrum analyzer because it's frequency very small
	Ref = 102dBμ BW = 100 KHz CF = 214 MHz CP1ΔF + 4.32 MHz 2 MHz / DIV ΔV + 18.8 dB Image Carrier Frequency LSB = 214 MHz - 4.32 MHz USB = 214 MHz + 4.32 MHz Voice carrier frequency: can not be seen by the spectrum analyzer because it's frequency very small
	Ref = 102dBμ BW = 100 KHz CF = 421 MHz CP1ΔF + 4.32 MHz 2 MHz / DIV ΔV + 18.8 dB Image carrier frequency: LSB = 421 MHz - 4.32 MHz USB = 421 MHz + 4.32 MHz Voice carrier frequency: can not be seen by the spectrum analyzer because it's frequency very small
	Ref = 102dBμ BW = 100 KHz CF = 624 MHz CP1ΔF + 4.32 MHz 2 MHz / DIV ΔV + 18.8 dB Image Carrier Frequency: LSB = 624 MHz - 4,32 MHz USB= 624 MHz + 4,32 MHz Voice carrier frequency: can not be seen by the spectrum analyzer because it's frequency very small
	Ref = 102dBμ BW = 100 KHz CF = 831 MHz CP1ΔF + 4.32 MHz 2 MHz / DIV ΔV + 18.8 dB Image Carrier Frequency: LSB = 831 MHz - 4.32 MHz USB = 831 MHz + 4.32 MHz Voice carrier frequency: can not be seen by the spectrum analyzer because it's frequency very small
	Ref = 102dBμ BW = 100 KHz CF = 1055 MHz CP1ΔF + 4.32 MHz 2 MHz / DIV ΔV + 18.8 dB Image Carrier Frequency: LSB = 1055 MHz - 4.32 MHz USB = 1055 MHz + 4.32 MHz Voice carrier frequency: can not be seen by the spectrum analyzer because it's frequency very small

DATA ANALYSIS:

From the spectrum image that we get, we can know that the value of:

Carrier frequency: 421 MHz

CP1ΔF + 4.32 MHz

Then:

USB = 421 MHz + 4.32 MHz = 425.32 MHz

LSB = 421 MHz - 4.32 MHz = 416.68 MHz

Voice carrier frequency: can not be seen by the spectrum analyzer because it's frequency very smaller than the frequency carrier.

For the multiples frequencies:

• 1^st multiple : 5 MHz
  
• 2^nd multiple : 214 MHz
  
• 3^rd multiples : 624 MHz
  
• 4^th multiples : 813 MHz
  
• 5^th multiples : 1055 MHz

QUESTION'S ANSWER:

1. Modulation system that being use in the video are AMPLITUDE MODULATION, because the signal amplitude information affect the amplitude of the carrier signal, the signal information into the cover of the carrier signal.
   

Image Modulated Signal

A common use of signal Am is: AM radio broadcasting is widely used for broadcast AM radio wave signal, the TV image (Video), Radio communication: aircraft, amateur radio (SSB), CB radio (Citizens Band Radio). Digital data transmission: Modems Computers (combined with QAM modulation)

1. This type of modulation is amplitude modulation and it can be seen from the changes in amplitude and has a spectrum of AM.
   

Based on the equation of the spectrum signal AM modulated, AM will have 3 (three frequencies):

• fc: carrier frequency signal
  
• LSB: Lower Side Band frequency (LSB), namely the difference between frequency carrier signal and the signal information.
  
• USB: Upper Side Band frequency (USB) is the addition of carrier signal frequency and signal information.
  

CONCLUSION

1. Video modulator is using amplitude modulation (AM)
   
2. AM modulation that shown on a spectrum analyzer displays are three frequencies namely
   

• Carrier frequency (fc)
  
• Lower Side Band Frequency (LSB)
  
• Upper Side Band Frequency (USB)
  

1. The difference between USB and LSB frequencies are = 4.32 MHz
   
2. Using 100 KHz bandwidth