Audio Video Transmitter & Receiver (AVTR)

Substance:

VHF tuner
UHF tuner
CHATODE RAY TUBE (CRT)
SYNCRONISATION SEPARATOR (SYNC SEPARATOR / Synchronization Separator)
Vertical OSC
Vertical Drive
Vertical OUT
Video Intermediate Frequency Amplifier (VIF / Picture IF Amplifier)
Video Detector
Video Drive
Automatic Gain Control (AGC)
Video Out
Horizontal Automatic Frequency Control (H-AFC)
HOR.DEFLECTION OSC (H.OSC)
HOR.DRIVE
HOR.OUT
Fly Back Transformer (FBT)
HIGH VOLTAGE RECTIFIER (HV.REC)
SOUND IF AMPLIFIER (SIF)
AUDIO DETECTOR (AUDIO.DET)
AUDIO OUT
PAL STANDARD LUMINANCE AND CHROMINANCE SIGNAL IN COLOR TV
LUMINANT SIGNAL
COLOR DIFFERENCE SIGNAL
TRANSMITTER SYSTEM (STANDARD PAL COLOR CODING)

1. VHF tuner

Consisting of RF amplifier (Radio Frequency Amplifier) local oscillator and mixer (Mixer), the tuner section is always separated from other parts to prevent interference, image and sound signals sent from the transmitter station, are given to this RF amplifier, all VHF Channel 2-12 (47 Mhz - 230 Mhz) station transmitters can be amplified by this RF amplifier section. The function of the RF amplifier is to increase the signal to noise ratio (signal to noise ratio) the RF amplifier output is converted to intermediate frequency (IF / Intermediate Freq.) through a process called "hate rodyning" this process is done when the RF amplifier output and the local oscillator output are combined / mixed in the mixer to form an IF signal, the local OSC signal generates a signal that is mixed with the RF signal from the selected channel to form an IF signal Gb. (38.9 Mhz) and sound signal (33.4 Mhz).

2. UHF tuner

Operated by selecting the UHF position on the VHF tuner. The UHF tuner has its own oscillator and mixer, which mixer and oscillator work to produce the IF signal Figure 38.9 Mhz and the IF signal of the voice 33.4 Mhz, this IF signal is given to the VHF tuner when the UHF tuner is working, the RF Level and Mixer in the VHF tuner function as an IF amplifier.

3. Cathode Ray Tube (CRT)

The video signal that has been amplified in the video output section is given to the cathode of the picture tube, the picture signal / video signal which is a conversion of light at the transmitter station, is converted back into the original light in this tube section.

4. Synchronization Separator (Sync. Separator / Synchronization Separator)

In this circuit, the synchronization pulse is separated from the composite output sync-sep video signal and then given to a filter circuit, namely a resistor that only passes the vertical synchronization pulse. This pulse is then given to the vertical OSC, the other part of the sync-sep output is given directly to the horizontal automatic frequency control (AFC).

5. Vertical OSC

The vertical OSC always oscillates at a frequency of 50 Hz even if the signal from the transmitter is not received, the OSC must continue to work so that the raster will appear on the screen, if the oscillation stops, a horizontal line appears on the screen and this will burn the CRT tube causing permanent damage. If a TV signal is received from a TV transmitter, a vertical sync signal is given to the vertical deflector OSC then the vertical OSC occurs at the same frequency and phase as the vertical oscillation at the transmitter station.

6. Vertical Drive

This section is an amplifier circuit that is needed to provide sufficient amplification to drive the vertical out circuit, the vertical drive as an impedance match between the vertical oscillator section and the vertical out section.

7. Vertical OUT

This section is a vertical deflection amplifier circuit. This amplifier provides sufficient scanning current to the deflection yoke so that the raster can fill the screen. The vertical scanning signal is amplified and given to the deflection coil on the neck of the CRT tube.

8. Video Intermediate Frequency Amplifier (VIF / Image IF Amplifier)

IF Image 38.9 Mhz and IF Sound 33.4 Mhz coming from the Mixer are given as VIF AMP input. The function of this amplifier is to amplify the IF signal so that it has a large enough voltage for the video detector.

9. Video Detector

In this detector, the composite video signal is detected and modulated from the IF signal, the composite video signal can be detected using a diode / transistor.

10. Video Drive

The function of this section is to separate the sound signal from the image signal, by using a 5.5 Mhz tuner circuit and a 5.5 Mhz (trap) circuit, the tuner circuit only passes 5.5 Mhz which contains the sound intermediate frequency (voice IF signal / SIF), this SIF signal is given and amplified by the SIF AMP, each 5.5 Mhz (often called a 5.5 Mhz trap) prevents the 5.5 Mhz SIF signal from entering the Video out section so that it can interfere with the composite Video signal, while the Composite signal is amplified by the Video Drive and then given to the video out section without being mixed with the sound signal.

11. Automatic Gain Control (AGC)

Sudden increase of signal received by antenna can cause distortion in image, to prevent this distortion then output level of video drive should be attempted at 1.0 - 1.5 Vp-p. AGC sends DC Feedback signal to RF amplifier and VIF amplifier. This DC voltage reduces bias of amplifier circuit which finally decreases decreasing gain which compensates large input signal from antenna.

12. Video Out

This section receives the Video signal from the drive section, the function of the video out section is to amplify the video signal so that the signal will be large enough to turn on the picture tube. The video out section is equipped with a contrast and brightness regulator in the form of a VR that varies the voltage difference between the cathode and the first gnd, the voltage difference controls the brightness.

13. Horizontal Automatic Frequency Control (H-AFC)

AFC.HOR circuit, located between sync-sep and OSC.HOR AFC has 2 inputs, the first from sync-sep and the second from Fly Black Transformer (FBT) / HOR.OUT, AFC circuit functions to maintain / keep the scanning frequency exactly 15,625 Hz, the method is by comparing the scanning pulse from sync-sep with the HOR output signal. or FBT, if there is a difference between the two, then AFC will send an OSC HOR signal to correct the frequency so that it is exactly 15,625 Hz

14. Hor. Deflection Osc (H.Osc)

It is a circuit placed between HOR.AFC and HOR.DRIVE. HOR.OSC functions almost the same as OSC.DEFLECTION VERTICAL. OSC.HOR oscillates at a frequency of 15,625 Hz. When the TV signal from the transmitting station has been received, the oscillator circuit oscillates / generates waves at the same frequency and phase as the broadcast studio / TV transmitter.

15. HOR. DRIVE

This section is an amplifier circuit that provides HOR turn signal amplification so that it can move the HOR.OUT circuit.

16. HOR.OUT

This circuit amplifies the signal from the HOR.DRIVE output in this block which is given to the HOR deflection coil to deflect the electron beam (path) towards the flat (HOR) and to the Fly back transformer (FBT) to produce high voltage for the CRT anode. In this HOR.OUT circuit, it consumes the most power compared to other parts of the circuit.

17. Fly Back Transformer (FBT)

The pulse from the HOR.OUT block is given to the primary side of the FBT, then the FBT increases the pulse voltage level to 10KVolt, up to 15 Kvolt then the high voltage pulse is fed into the rectifier wave rectifier.

18. HIGH VOLTAGE RECTIFIER (HV.REC)

High voltage from Fly back Transformer (AC) must be rectified to (DC) so that a high positive voltage is produced for the CRT anode, the rectifier that is often used is a selenium diode, a high breakdown voltage that is able to withstand high voltage from FBT a Capacitor should be used to smooth the results of the voltage rectifier but in this rectifier it is replaced by a CRT tunnel that functions as a Giant Capacitor, so you can imagine a capacitor as big as a CRT. so the high voltage is approximately the same as the size of the tube (in inches) multiplied by 1KVolt for example for a 12 x 1Kvolt tube = 12 K.volt.

19. SOUND IF AMPLIFIER (SIF)

Sound Intermediate Frequency (SIF) Amplifier / intermediate frequency amplifier serves to amplify the modulated 5.5 MHz signal sent from the video drive. This SIF amplifier section also has another function, namely as a signal cutter / limiter, to eliminate noise. Noise in the FM signal will appear as an increase in the Amplitude of this distortion is eliminated using a limiter circuit.

20. AUDIO DETECTOR (AUDIO DET.)

Amplitude Distortion

Functions to demodulate or retrieve the sound signal from the FM carrier wave sent from the SIF AMP. The center frequency of this wave is 5.5 Mhz and the Max. and Min. deviation from the Center Frequency -+ 50KHz detection characteristics can be described by the "S" curve. In FM, the amplitude of the sound signal depends on the frequency of the modulated carrier wave if the detector circuit is not adjusted properly, the center frequency can shift from 5.5 Mhz, then the detection of the sound signal uses a non-linear "S" curve and will result in distortion in the sound.

21. AUDIO OUT

The function of this block is to amplify the audio signal sent from the detector so that the signal is large enough / strong enough to move the LS, this section is also equipped with a variable resistor to adjust the sound volume.

22. PAL Standard Luminance Signal & Chrominance Signal in Color TV

The image dots on a color TV signal must be visible on a black and white TV receiver.
The black and white TV waveform image dots should be visible on a color TV receiver.

To meet these requirements, a luminance signal must be transmitted which regulates the brightness of the received image (the same nature as a black and white TV video signal) and a chrominance signal which regulates the color level and chroma formed from 3 primary colors (RGB), below is an example of a color TV schematic;

Color Camera Block Diagram

In this way, if a color TV broadcast is received by a black and white TV, then only the luminance signal is useful, whereas if it is received by a color TV, the luminance signal and the chrominance signal are both used for further processing so that they can display primary colors (RGB).

23. LUMINANT SIGNAL

Made from 3 signal colors as captured by the camera, then mixed in a fixed ratio using a MATRIX circuit, because the human eye is sensitive to the highest light intensity in green, then in red and the last is blue, the mixing is made by showing the sensitivity properties, namely the components of each camera output signal are mixed with a ratio of 59% green, 30% red and 110% blue, this ratio is shown as follows

EY = 0.299 ER + 0.587 EG + 0.114 EB

24. COLOR DIFFERENCE SIGNAL

In a composite color TV signal, there are other signals except the luminance signal (EY) which provides messages (information) about color and chroma levels, namely the color difference signal represented by ER - EY AND EB - EY, this color difference signal is also formed from primary colors, namely by subtracting the luminance signal through a matrix circuit. In the actual circuit, the luminance signal with opposite polarity is mixed with the primary color signal.

25. TRANSMITTER SYSTEM (STANDARD PAL COLOR CODING)

In the standard color TV system, the luminance signal = black and white TV video signal and the two color difference signals (ER-EY) and (EB-EY) are transmitted together on a color frequency plane to 1.3 Mhz. Based on the characteristics of the human eye, in general if a signal is broadcast via a radio wave, a carrier wave is needed, if the 3 signals are broadcast via radio waves, then 3 carrier radio waves are needed.

In color TV, in order to have compatible properties, the luminance signal must be broadcast with the same carrier wave as in black and white TV, in color difference signals, different sub carrier waves are used in the frequency plane of the luminance signal and the modulation method used is called suppressed carrier amplitude modulation (balanced modulation) with this modulation system, both color difference signals can be broadcast without interfering with each other.

TV Mixer

The image above shows a non-PAL transmission system (color encoder), in this system there are 3 types of color sub carriers with a frequency of 4.43361875 Mhz and have a phase of 0, 90 and 180 degrees by inserting a color sub carrier that has a phase of 90 degrees and an EB-EY signal on the balanced modulator M1, then a sub carrier signal is produced that is modulated with EB-EY in a balanced modulation, then by alternately inserting, a color sub carrier that has a phase of 0 degrees and 180 degrees for each opposite row into the balanced modulator m2, then a balanced modulated sub carrier signal ER-EY can be produced. After balanced modulation, the modulated output is mixed and the result is called the color carrier signal and the signal is broadcast together with the luminance signal and the two signals (EB-EY) (ER-EY) are summed on two balanced modulators, because the signals depend on the chromatization of the color level and the chroma of the object, so the output of the balanced modulator changes automatically and the composite signal of the color sub carrier also changes.