RegisterHomeForumsGallerySearchFAQMemberlistLog in
Front End Circuit and Fundamentals of Digital Video Processi

 
Reply to topic    DOST-SEI Online :: [Scholars and Alumni Community] Forum Index » Knowledge Resource Center View previous topic
View next topic
Front End Circuit and Fundamentals of Digital Video Processi
Author Message
administrator
DOST-SEI Administrator
DOST-SEI Administrator


Joined: 12 Jun 2006
Posts: 220
Location: Singapore, Singapore

Post Front End Circuit and Fundamentals of Digital Video Processi Reply with quote
Front End Circuit and Fundamentals of Digital Video Processing

VHF and UHF Comparable Tuning

On a given receiver, use of the UHF and VHF tuning systems shall provide approximately the same degree of tuning accuracy with approximately the same expenditure of time and effort: Provided, however, That this requirement will be considered to be met if the need for routine fine tuning is eliminated on UHF channels.

Basic tuning mechanism. If a TV broadcast receiver is equipped to provide for repeated access to VHF television channels at discrete tuning positions, that receiver shall be equipped to provide for repeated access to a minimum of six UHF television channels at discrete tuning positions. Unless a discrete tuning position is provided for each channel allocated to UHF television, each position shall be readily adjustable to a particular UHF channel by the user without the use of tools. If 12 or fewer discrete tuning positions are provided, each position shall be adjustable to receive any channel allocated to UHF television.

The combination of detented rotary switch and pushbutton controls is acceptable, provided UHF channels, after their initial selection, can be accurately tuned with an expenditure of time and effort approximately the same as that used in accurately tuning VHF channels. A UHF tuning system comprising five pushbuttons and a separate manual tuning knob is considered to provide repeated access to six channels at discrete tuning positions. A one-knob (VHF/UHF) tuning system providing repeated access to 11 or more discrete tuning positions is also acceptable, provided each of the tuning positions is readily adjustable, without the use of tools, to receive any UHF channel.

Tuning controls and channel readout. UHF tuning controls and channel readout on a given receiver shall be comparable in size, location, accessibility and legibility to VHF controls and readout on that receiver.

Differences between UHF and VHF channel readout that follow directly from the larger number of UHF television channels available are acceptable if it is clear that a good faith effort to comply with the provisions of this section has been made.

If equipment and controls that tend to simplify, expedite or perfect the reception of television signals (e.g., AFC, visual aids, remote control, or signal seeking capability referred to generally as tuning aids) are incorporated into the VHF portion of a TV broadcast receiver, tuning aids of the same type and comparable capability and quality shall be provided for the UHF portion of that receiver.

If a television receiver has an antenna affixed to the VHF antenna terminals, it must have an antenna designed for and capable of receiving all UHF television channels affixed to the UHF antenna terminals. If a VHF antenna is provided with but not affixed to a receiver, a UHF antenna shall be provided with the receiver.

The picture sensitivity of a TV broadcast receiver averaged for all channels between 14 and 69 inclusive shall not be more than 8dB larger than the peak picture sensitivity of that receiver averaged for all channels between 2 and 13 inclusive.

The noise figure for any television channel 14 to 69 inclusive shall not exceed 14 dB. A TV receiver model is considered to comply with this noise figure if the maximum noise figure for channels 14-69 inclusive of 97.5% of all receivers within that model does not exceed 14 dB.



VHF Tuners

Tunes Very High Frequency. VHF has the range of electromagnetic frequencies from 30MHz to 300MHz. A portion of the frequency spectrum, approx. 32 to 316 megahertz. VHF transmissions are used for marine radio telephony, most commonly used up to 50 nautical miles offshore.


UHF Tuners

Tunes Ultra High Frequency. UHF is any radio frequency in the 300- to 3,000-MHz range. In television use, refers to the set of frequencies starting at 470 MHz, The UHF channels are designated as 14 through 70. Unicast A unicast application transmits a copy of every packet to every receiver. The band of television broadcast frequencies reserved by the FCC for local and community-access stations, local weather services, stock reports, etc.



Drum-Type Tuner

An old fashioned television tuner usually situated at the front-right side of a television. It is a circular tuner, also known as a ?twist type tuner?. It is more like a rotary swith, used in selecting channels. Drum Type Tuner selects TV channels by rotating it clockwise or counter-clockwise.

Switch-Type Tuner

An old type of television tuner that is found at the front of a TV. It is a group of buttons, usually from 1-10, that represents the channels available to be viewed in the screen of the TV. Controls the traffic flow of frames across a network by providing a dedicated connection. Switches operate at the data link layer. It is also a tuner which has a network device that selects a path or circuit for sending a unit of data to its next destination.



Electronic Tuning

The process of tuning or selecting appropriate signals for the circuit to meet its proper biasing by using electronic devices and components. Electronic tuner is device for tuning which consists of an inductor and capacitor or an inductor, capacitor and resistor so connected and resistor so connected as to form a resonance circuit, the mean frequency or channel to which the tuner is resonant being variable. The resistance may be in the form of the inherent resistance of the circuit or a lumped resistance element connected in the circuit. It is also a device for selecting, especially an electronic circuit or device used to select signals at a specific radio frequency for amplification and conversion to sound.



The Oscillator

A circuit that creates a carrier wave at the desired frequency. The three most common methods of controlling the frequency are PLL, VFO, and crystal. In the latter method, a piece of quartz crystal that vibrates at the chosen frequency governs the circuit

The RF Amplifier

You put a weak radio signal in, and a stronger signal comes out, this is the basic function of a RF amplifier circuit.

The Mixer

An audio console, which is capable of equalizing and adjusting volume and direction. Most sophisticated edit systems route the source audio through a mixer rather than directly into the record machine; this way, the audio can be adjusted as needed.


Tuner Troubleshooting

Step 1 Check the voltage at U7401-10 (5VDC). This will verify B+ and establish a good ground.

Step 2 Monitor the voltage at Q7401-C Tuner Control. If the voltage is changing when you change channels this would indicate U7401 is working.

Step 3 Check the voltage at U7501-4 Quad Op Amp. This is the 33 volt used for channel tuning.

Step 4 Monitor the voltage at Q7402-c Band Switch Transistor. You should have a negative DC voltage for band 1 (-11 to -14 VDC). You should have a positive DC voltage for band 2 (+11 VDC). This will switch positive or negative as you change bands.

Step 5 Monitor the voltage at U7401-9 Mixer/OSC. This is the band switch used at U7301-7. 3 VDC activates the VHF OSC at pin 11. When UHF is selected, U7301-7 should go to 0 VDC. The UHF OSC at U7301-14 should be running. When OSC isn't running the voltage is about 10 to 11 VDC and when the OSC is running the voltage will measure about 4.5 to 5 VCD. Another good thing to know is that if U7301-1 is low (less than 5 VDC) the chip is probably bad and the tuner alignment won't respond because the RF AGC will remain high.

Step 6 The voltage at U7401-9 is also used for RF Band Switch. Q7403 and Q7404 collectors are connected together and the state of the common collectors determines the VHF/UHF RF switching. When the voltage at U7401-9 is high (7 VDC), Q7403 turns on. Its collector is 0 VDC and the VHF RF amp Q7102 is turned on by lowering the source voltage to about 4.5 to 5 VDC. When U7401-9 is low (0 VDC), Q7404 turns on. The collector is high (11 VDC). Q7102-S will go high turning the UHF RF amp off. At the same time Q7101-D (UHF RF amp) goes high and the UHF RF amp is turned on. An overview would be when a VHF band is selected, U7401-9 is 7 VDC. You should have 3 VDC at U7301-7. The VHF Mixer/OSC will be running and the voltage at U7301-11 will be about 4.5 to 5 VDC. Q7403 will be in saturation and the collector is at 0 VDC. When U7401-9 is 0 VDC, U7301-7 is 0 VDC and the UHF Mixer/OSC is selected. U7401-14 will now measure about 4.5 to 5 VDC. Q7404 will turn on, collector is high and the UHF RF amp is selected.



Step 7 Q7401 off U7401-14 is the Tuning PLL Transistor Its collector is used to control the 33 VDC for tuning. This voltage is used at U7301-3 as a tuning reference for the QUAD OP AMP. The digital information stored in the eeprom comes into U7501 pins 5,10 and 12. This information is converted to an analog value at pins 7,8 and 14 and used to tune the varactor diodes to band pass the selected channel frequency. You can use a DVM to measure the voltage at U7501 pin 3. This is the tuning reference. Selecting channel 2, you should have about 1.35 VDC on pin 3 and about 1 VDC at pins 7,8 and 14. Selecting channel 13, the voltage at pin 3 is about 2.01 VDC. Pins 7,8 and 14 about 6 VDC. Now you should go to the varactor diodes and measure approximately the same voltage at their cathodes. (Keep in mind that these voltages will change as you chage channels). When in the air mode, you may use the chart at the bottom page 49 in the CTC 175/176/177 training manual for reference. When in the cable mode, use the chart on page 51. VARACTOR DIODES are designed such that their capacitance is dependent on the voltage across the diode. As the tuning voltage varies across the diode, a varactor acts like a variable capacitor causing the tuned circuit to vary its frequency. Different channels are tuned in this manner. (Note: Varactor diodes work with reverse bias).




VHF Tuner Alignment

If the VHF tuner alignment needs adjustment, the set may give distorted reception and lack sensitivity. If the set has a tuning indicator, the best reception may not occur at maximum indication. Bear in mind however that valve VHF sets are not as sensitive as modern transistor designs, so you could only expect to receive stronger signals such as the BBC national programmes and your local stations.



For this discussion, we will use the Ekco C273 circuit again. Connect a voltmeter across the ratio discriminator capacitor (C28) to act as a level meter. Switch the set to VHF and disconnect the aerial. The meter should read less than 1V.
Set the signal generator to the expected IF (normally 10.7MHz) and switch the internal modulation OFF. Connect the signal generator between one of the aerial sockets and the chassis via 0.01uF capacitors as previously. Vary the signal generator frequency around the expected IF, and try to find a peak. If the IF adjustment is OK you will find one clearly defined peak.
If not, adjust the cores of the VHF IF transformers for maximum reading on the meter. Start with the transformer closest to the tuner (L6/L7) and work forward. The first IF transformer is normally in the VHF tuner unit. Adjust the RF level as necessary to keep the output meter reading at about 4V.
Before adjusting the final IF transformer, you need to establish which core is the secondary. With vertical cans it is often (but not always) the top adjustment. If you have the service sheet you can check this, otherwise try adjusting them both slightly. The primary adjustment should peak in the same way as the other IF transformers and can be adjusted as previously. If it is still not clear, you may have to carefully dismantle the transformer to check.
The setting of the final IF secondary affects the performance of the ratio discriminator circuit. The various service sheets describe different methods of doing this, some requiring specialised equipment. I normally ignore these, and use the method that is described here. It requires no specialised equipment and works fine. It is based on the method described in most Bush service sheets.
Connect two 100K 1% resistors in series, across C28. Note that the comparative accuracy of the resistors is more important than the absolute value - they can be 68K, 82K, 100K or 120K as long as they are both the same value and are both 1% components. Connect a micro-ammeter between the junction of these resistors and the junction of R10 and C24. With the signal generator connected as previously, adjust the core of the secondary of the final IF transformer for a reading of zero on the micro-ammeter. This will be between a positive and negative peak.
It is possible to align the VHF IF stages without a signal generator by tuning to a fairly strong transmission and carrying out the adjustments as described above. BBC Radio 3 is a good choice because it is generally quieter than the other stations, and therefore there is less modulation to confuse the results. Of course, this assumes that the set is receptive enough to receive something before you start. The most tricky part to do by ear is the ratio discriminator.

Fundamentals of Digital Video Processing

JPEG

JPEG is a standardized image compression mechanism. JPEG stands for Joint Photographic Experts Group, the original name of the committee that wrote the standard. JPEG is designed for compressing either full-color or gray-scale images. A
JPEG (pronounced JAY-peg) is a graphic image created by choosing from a range of compression qualities (actually, from one of a suite of compression algorithms). When you create a JPEG or convert an image from another format to a JPEG, you are asked to specify the quality of image you want. Since the highest quality results in the largest file, you can make a trade-off between image quality and file size. Formally, the JPEG file format is ISO standard 10918. The JPEG scheme includes 29 distinct coding processes although a JPEG implementer may not use them all.
A form of image compression that reduces the size of a graphic file by discarding some image data. JPEG compression can make a file very small, but it is "lossy," meaning that image quality is lost when the image is compressed. JPEG compression is generally suitable only for use on the World Wide Web; it is not generally considered appropriate for print images. LZW compression is preferable for high-quality images that must be reduced in size. (JPEG stands for Joint Photographic Experts Group, the industry body that created it.)

MPEG
Moving Picture Experts Group. The standard for compression and storage of motion video, for example, videos available though the World Wide Web.
MPEG (pronounced EHM-pehg), the Moving Picture Experts Group, develops standards for digital video and digital audio compression. It operates under the auspices of the International Organization for Standardization (ISO). The MPEG standards are an evolving series, each designed for a different purpose.
(Moving Picture Experts Group) - Pronounced m-peg, a working group of ISO. The term also refers to the family of digital video compression standards and file formats developed by the group. MPEG generally produces better-quality video than competing formats, such as Video for Windows, Indeo and QuickTime. MPEG files can be decoded by special hardware or by software.
Motion Picture Experts Group. A committee of experts from the audio, video, and computer industries developing an evolving series of standards for compression of moving images. Files encoded using this standard are referred to as MPEG files. MPEG-1 is a low-resolution format currently used on the World Wide Web for short animated files. MPEG-2 is a much higher resolution format being developed for digital television and movies.
MPEG (Moving Picture Experts Group) is an ISO (International Organization for Standardization) / ITU (International Telecommunication Union) standard for compressing video. It also stands for the group name. MPEG are developing new standards with the advance of technology, so that MPEG standards are evolving in series, each designed for a different purpose. The number following MPEG indicates each standard, for example, MPEG-1, MPEG-2, MPEG-3. For the MPEG file extension, "Mpg" is used.
Moving Pictures Experts Group. A format for moving images (video). MPEG compresses at about a 50 to 1 (50:1) ratio before visible degradation occurs. Compression can go as high as about 200:1. A good working figure is about 1.2 to 1.5 megabytes (MB) for each second of MPEG video.

_________________

We live among you, hidden in plain sight, we have a different language, but we don't speak it, we are elite, but we don't flaunt it, we are different, but we are on...
DOST-SEI Alumni Community :: DOST-SEI Web Mail
Tue Jun 27, 2006 5:12 pm View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger ICQ Number
ice
Intel Duo Data Analyst
Intel Duo Data Analyst


Joined: 26 Jun 2006
Posts: 2129
Location: Davao City

Post Reply with quote
gosh

dapat pala nakita ko eto before kasi nan dito lahat un assignment namin sa TGY9 gosh

sayang

sige lang...

next time ulit

_________________

Ice Co. & Chili Cool Site | Aice Nice Concepts | Isis' Insights
Sat Jul 01, 2006 7:46 pm View user's profile Send private message Visit poster's website Yahoo Messenger MSN Messenger
JHL
DOST-SEI Administrator
DOST-SEI Administrator


Joined: 12 Jun 2006
Posts: 1683
Location: Davao City

Post Reply with quote
hhehehe,, uu pinopost namin dito yung mga assignment, lalo na kay sir blancia, nyahahaha

_________________

Nursing Jobs Abroad :: Cebu Pacific
Tue Jul 04, 2006 9:16 am View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger ICQ Number
administrator
DOST-SEI Administrator
DOST-SEI Administrator


Joined: 12 Jun 2006
Posts: 220
Location: Singapore, Singapore

Post Reply with quote
Copy paste mo lang isis if you need this one..

_________________

We live among you, hidden in plain sight, we have a different language, but we don't speak it, we are elite, but we don't flaunt it, we are different, but we are on...
DOST-SEI Alumni Community :: DOST-SEI Web Mail
Tue May 15, 2007 3:38 pm View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger ICQ Number
tanom
Intel Duo Data Analyst
Intel Duo Data Analyst


Joined: 26 Apr 2007
Posts: 2159
Location: Pilipinas, Game ka na ba?!

Post Reply with quote
hay naku.. ang ganda pa naman ng process kaya lang.. ang haba... di ko tuloy natapos sa pagbasa,,,

_________________
Thanks and best regards,
MMM
please visit:
http://www.bugits..com
http://euts.wordpress.com
http://bisrocklyrics.blogspot.com
Tue May 15, 2007 11:26 pm View user's profile Send private message Visit poster's website
ice
Intel Duo Data Analyst
Intel Duo Data Analyst


Joined: 26 Jun 2006
Posts: 2129
Location: Davao City

Post Reply with quote
siguro naman ngayon tapos mo na? Blue_PDT_01_12

_________________

Ice Co. & Chili Cool Site | Aice Nice Concepts | Isis' Insights
Sat May 26, 2007 12:19 am View user's profile Send private message Visit poster's website Yahoo Messenger MSN Messenger
ferdinand_lozada
Intel Duo Data Analyst
Intel Duo Data Analyst


Joined: 08 May 2007
Posts: 1036
Location: Kuala Lumpur

Post Reply with quote
OKAY ITONG INFORMATION NA PINOST DITO AH! GALING! Blue_PDT_01_12
Sun Jun 10, 2007 12:30 pm View user's profile Send private message AIM Address Yahoo Messenger MSN Messenger
ice
Intel Duo Data Analyst
Intel Duo Data Analyst


Joined: 26 Jun 2006
Posts: 2129
Location: Davao City

Post Reply with quote
ferdinand_lozada wrote:
OKAY ITONG INFORMATION NA PINOST DITO AH! GALING! Blue_PDT_01_12



Wow ferds! binasa mo lahat lahat? or talagang alam mo na parang review mo nalang
Blue_PDT_01_12

_________________

Ice Co. & Chili Cool Site | Aice Nice Concepts | Isis' Insights
Sun Jun 10, 2007 12:35 pm View user's profile Send private message Visit poster's website Yahoo Messenger MSN Messenger
ferdinand_lozada
Intel Duo Data Analyst
Intel Duo Data Analyst


Joined: 08 May 2007
Posts: 1036
Location: Kuala Lumpur

Post Reply with quote
AHEHEH.. SUBJECT DIN PO KASI NAMIN IYAN DATI... MERON NGA RIN ATA LUMABAS REGARDING MPEG AT JPEG SA BOARD EXAMS... KAYA NICE INFORMATION IYONG NAPOST NI ADMIN... AHEHE!
GREAT! Blue_PDT_01_12

Sun Jun 10, 2007 12:42 pm View user's profile Send private message AIM Address Yahoo Messenger MSN Messenger
ice
Intel Duo Data Analyst
Intel Duo Data Analyst


Joined: 26 Jun 2006
Posts: 2129
Location: Davao City

Post Reply with quote
ferdinand_lozada wrote:
AHEHEH.. SUBJECT DIN PO KASI NAMIN IYAN DATI... MERON NGA RIN ATA LUMABAS REGARDING MPEG AT JPEG SA BOARD EXAMS... KAYA NICE INFORMATION IYONG NAPOST NI ADMIN... AHEHE!
GREAT! Blue_PDT_01_12



sa exam din ng TESDA meron lumabas about jpeg and mpeg
Blue_PDT_01_12

_________________

Ice Co. & Chili Cool Site | Aice Nice Concepts | Isis' Insights
Sun Jun 10, 2007 12:52 pm View user's profile Send private message Visit poster's website Yahoo Messenger MSN Messenger
asanist_13
Freshmen
Freshmen


Joined: 01 Dec 2008
Posts: 7
Location: cavite

Post Sayang... Reply with quote
Sana pinanganak din akong matalino kagaya nyo.. Blue_PDT_01_01 [/b]

_________________
"In this world, it doesn't matter WHERE or HOW long you lived your life..
What matters most, is WHAT you did within your lifetime..."
Mon Dec 08, 2008 8:01 pm View user's profile Send private message Send e-mail AIM Address Yahoo Messenger MSN Messenger
diomari
Genuine Prime Mover
Genuine Prime Mover


Joined: 25 May 2008
Posts: 29
Location: Tagum City

Post Tsok! Reply with quote
Waw! Gud information. Magagamit q to in d future. Hehehe. At d min tym. Nosebleed muna. Hahahaha.

_________________
Kupal mag Drupal^^
Tue Mar 10, 2009 11:42 pm View user's profile Send private message AIM Address Yahoo Messenger MSN Messenger
Display posts from previous:    
Reply to topic    DOST-SEI Online :: [Scholars and Alumni Community] Forum Index » Knowledge Resource Center All times are GMT + 8 Hours
Page 1 of 1

 
Jump to: 
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Copyright © 2006 - 2013. DOST-SEI Scholars Online Community. All Rights Reserved