EXPERIMENT 2 MODULATOR VIDEO

Objectives:

1. Measuring the frequency spectrum of video transmission.
2. Determine the carrier frequency range image and sound carrier frequency.
3. Specifies the field width (bandwidth) on video transmission.
4. Specify the type of modulation on the picture and sound.



Equipment Used:
 
1 Modulator video (VCD / VTR / video sender).
1 A Spectrum Analyzer.
1 An RCA cable connector - BNC

Circuit diagram:

 Introduction:

           How to emit (transmit) signal is amplitude modulated image 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. Modulation is a signal of fundamental frequency (baseband). On television, this baseband signal is a composite video signal. Broadcast television is really such a radio system, but includes pictures and sound. Sound signal emitted by joining in it frequency modulation (FM) on a separate carrier wave transmitter in the same channel as the image signal.

Understanding the image signal is used here to mean a modulated carrier wave. The video signal is a signal to a picture tube. Video signal to television audio signal corresponds to the sound system. 

Details are clearer than the image signal AM (amplitude modulation picture) and an FM voice signal.

 

                 (a) without VSB 

         (b) with VSB

  Figure. 2 

         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). 

Basic theory

Vestigial sideband (VSB)

A vestigial sideband (in radio communication) is a sideband that has been only partly cut off or suppressed. Television broadcasts (in analog video formats) use this method if the video is transmitted in AM, due to the large bandwidth used. It may also be used in digital transmission, such as the ATSC standardized 8-VSB. The Milgo 4400/48 modem (circa 1967) used vestigial sideband and phase-shift keying to provide 4800-bit/s transmission over a 1600 Hz channel.

The video baseband signal used in TV in countries that use NTSC or ATSC has a bandwidth of 6 MHz. To conserve bandwidth, SSB would be desirable, but the video signal has significant low frequency content (average brightness) and has rectangular synchronising pulses. The engineering compromise is vestigial sideband modulation.

In vestigial sideband the full upper sideband of bandwidth W2 = 4 MHz is transmitted, but only W1 = 1.25 MHz of the lower sideband is transmitted, along with a carrier. This effectively makes the system AM at low modulation frequencies and SSB at high modulation frequencies. The absence of the lower sideband components at high frequencies must be compensated for, and this is done by the RF and IF filters.

Source : WIKIPEDIA.COM

Eksperimentele Procedure:

1. Kalibrasie Spektrum Analyzer die verwysing spektrum te bepaal.
2. Set-up instrumente soos in die foto hierbo.
3. OP die instrument.
4. Meet die uitset video modulator (RF) met behulp van die spektrum analiseerder en neem die frekwensie spektrum.
5. Beeld van die frekwensie spektrum.
6. Bepaal hoeveel 'n beeld draer frekwensie, draerfrekwensie klink, en die verskil frekwensie foto draer en' n goeie carrier frekwensie.
7. Waarneming van die spektrum, bepaal die tipe modulasie gebruik in die oordrag, by wyse van die verandering van die freq. SPAN (kleiner skaal).
8. Figuur spktrum frekwensies veelvoude van die basis frekwensie.

Question:
 
1. What system is used in the video modulator?
2. From step 6, how to know what types of modulation?

RESULT EXPERIMENT :

Gambar Spektrum Frekuensi	Keterangan
	Ref = 102dBµ BW = 100 KHz CF = 5 MHz CP1ΔF + 4,32 MHz 2 MHz / DIV ΔV + 18,8 dB Frekuensi Pembawa Gambar : LSB = 5 MHz - 4,32 MHz USB= 5 MHz + 4,32 MHz Frekuensi pembawa suara : tidak dapat dilihat dengan spectrum analyzer karena frekuensi sangat kecil
	Ref = 102dBµ BW = 100 KHz CF = 214 MHz CP1ΔF + 4,32 MHz 2 MHz / DIV ΔV + 18,8 dB Frekuensi Pembawa Gambar LSB = 214 MHz -  4,32 MHz USB= 214 MHz + 4,32 MHz Frekuensi pembawa suara : tidak dapat dilihat dengan spectrum analyzer karena frekuensi sangat kecil
	Ref = 102dBµ BW = 100 KHz CF = 421 MHz CP1ΔF + 4,32 MHz 2 MHz / DIV ΔV + 18,8 dB Frekuensi Pembawa gambar : LSB = 421 MHz - 4,32 MHz USB= 421 MHz + 4,32 MHz Frekuensi pembawa suara : tidak dapat dilihat dengan spectrum analyzer karena frekuensi sangat kecil
	Ref = 102dBµ BW = 100 KHz CF = 624 MHz CP1ΔF + 4,32 MHz 2 MHz / DIV ΔV + 18,8 dB Frekuensi Pembawa Gambar : LSB = 624 MHz - 4,32 MHz USB= 624 MHz + 4,32 MHz Frekuensi pembawa suara : tidak dapat dilihat dengan spectrum analyzer karena frekuensi sangat kecil
	Ref = 102dBµ BW = 100 KHz CF = 831 MHz CP1ΔF + 4,32 MHz 2 MHz / DIV ΔV + 18,8 dB Frekuensi Pembawa Gambar : LSB = 831 MHz - 4,32 MHz USB= 831 MHz + 4,32 MHz Frekuensi pembawa suara : tidak dapat dilihat dengan spectrum analyzer karena frekuensi sangat kecil
	Ref = 102dBµ BW = 100 KHz CF = 1055 MHz CP1ΔF + 4,32 MHz 2 MHz / DIV ΔV + 18,8 dB Frekuensi Pembawa Gambar : LSB = 1055 MHz - 4,32 MHz USB= 1055 MHz + 4,32 MHz Frekuensi pembawa suara : tidak dapat dilihat dengan spectrum analyzer karena frekuensi sangat kecil

DATA ANALYSIS
  
~ Viewed from the image spectrum that we get can we 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 because of the frequency spectrum analyzer with extremely small compared with the frequency carrier.

~ For multiple frequencies :

·    Multiples of 1 on the frequency: 5 MHz

·     Multiples of 2 on the frequency: 214 MHz

·     Multiples of 3 on the frequency: 624 MHz

·      Multiples of 4 on the frequency: 183 MHz

·      Multiples of 5 on the frequency: 1055 MHz

 ANSWERS TO QUESTIONS

1. Modulation system used 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.

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

 2. Known types of modulation are amplitude modulation can be seen from the changes in amplitude and has a spectrum of AM.

Based on the equation of the spectrum signal modulated AM AM will have 3 (three frequencies):
    • fc       : carrier frequency signal
    • LSB   : Lower Side Band frequency (LSB), namely the difference frequency carrier signal and the signal information.  
    • USB  : Upper Side Band frequency (USB) is the number of carrier signal frequency and signal  information.

                 

CONCLUSION :

1. In a video modulator that is used is amplitude modulation Modulation (AM)
2. AM modulation is shown on a spectrum analyzer displays the three frequencies namely
    - carrier frequency (fc)
    - Frequency of Lower Side Band (LSB)
    - Frequency of Upper Side Band (USB) 
3. The difference between USB and LSB frequencies are = 4.32 MHz
4. Used 100 KHz bandwidth.