The characteristics of a video signal and methods to overcome distance limitations Rich Hanna, CTS Regional Application Specialist, Southeast Extron Electronics Monday, January 24, 2005 9:00 AM 4:00 PM
Biography Rich Hanna, CTS Rich is Extron's Regional Applications Specialist, Southeast. Based in Atlanta, he is responsible for training and supporting Extron dealers, customers, and consultants. In addition, he is an ICIA adjunct faculty member. He has more than 29 years of engineering, installation, technical training, and sales experience in presentation and production video systems. Prior to joining Extron, Rich worked for the Broadcast/Professional Group of Sony Electronics Inc., Martin Marietta Aerospace, and the USAF. Extron is a commercial manufacturer of high performance computer video interface, processing, switching, and distribution products for the professional audio-visual industry.
Objectives Provide the student tools to recognize and deal with signal loss Be able to differentiate between; Level loss Peaking loss Explain bandwidth and its importance in systems Justify the use of different products to increase system performance
Agenda Cable & Signal loss Level/Peaking Bandwidth TP products
Cable The Weakest Link in a Video System
Attenuation (Cables) Measure of a cable s ability to transmit a signal References the loss of signal compared to its original level Cable has 3 variables Amount of loss -2.9 db Freq. where loss is measured 200MHz Distance or length of cable 100 Termination
Cable Resistance What it is: Opposition to the flow of electrons Spec is given in Ohms per 1000 feet Increases with length What it does: Lower voltage level at far end Longer cable = weaker signal at far end Shows as a lack of brightness in the video image Garden hose analogy Water Volume
Cable Capacitance What it is: Amount of electrical charge something can hold Ability of cable to charge and discharge How fast can the signal turn on or off What it does to video signals: Reduce the sharpness of the image Edges become fuzzy
Impedance What it is: Combination of resistance and reactance Determined by the complex resistance to the electromagnetic field inherent in the cable Cannot measure with an ohm meter How to deal with it: In order to maintain signal integrity, exact amount must be maintained throughout a system
Cable Loss Example Original picture at the source Picture at the far end, with signal loss
Cable Attenuation Examples Also known as insertion loss Nominal attenuation
What is smearing?
Installation concerns The number one, most important, absolutely crucial factor in all cable installations is? TERMINATION! Always ensure quality termination Training Proper tools
Individual Cable Length How critical is the length of each individual wire? The inverse of propagation delay x inverse of dot clock = # of feet for one pixel delay 1024 x 768 x 60 has a dot clock of 65 MHz 1/(1.3ns/ft) x (1/65 MHz) = 11.8 feet HOWEVER You can see the difference after (about) 3-4 feet
Compensating for Signal Loss
Compensating for Video Signal Loss Computer Video Interfaces Level / Peaking Control Level compensates for long distances Resistance Peaking compensates for multiple components Capacitance
Signal Attenuation Review Signal Attenuation Resistance Mainly affects the brightness of the image Capacitance Mainly affects the detail
Video Level Adjustment Original Signal After passing through compensation 200 LEVEL of cable
Video Peaking Adjustment Original Signal After passing compensation through Peaking 200 of cable
Peaking Effects on Image
Video Bandwidth Critical to system performance
What is bandwidth? The range of frequencies a product can pass without significant signal loss Any product that passes a signal, has a limited bandwidth
Bandwidth Specs What does a bandwidth spec look like? Bandwidth 425 MHz (-3dB), fully loaded How much does it pass? How well does it pass?
What kind of products have bandwidth specifications? Any fixed product that passes or processes a signal Interfaces Switchers Distribution amplifiers Projectors Monitors Cable? Test generators? Graphic cards? Human ear?
Important Frequencies Low Frequencies: Vertical Sync. Mid Frequencies: Horizontal Sync High Frequencies: Video Information 60-120 Hz 15-130 khz 5.5-130 MHz Video products only specify the upper critical frequency!
Bandwidth Loss How does it effect the image? Sharpness Brightness Vertical resolution
Define Our Video Signal What frequencies do we care about? 1024 x 768 @60 = 70.8 MHz 1280 x 1024 @60 = 118 MHz 1600 x 1200 @60 = 172 MHz The 300 to 400 MHz ( 3dB) point is important What about the 0-130 MHz performance?
Bandwidth Rule of Thumb Always use product that has 2 to 3 times the bandwidth of the original signal Ensures that your signal will be minimally impacted
Checking Bandwidth How are products swept? By using a spectrum, or network analyzer Analyzer output signal continually sweeps from a low to a high frequency Analyzer input side plots (displays) how much signal (+/-) comes back Gains / losses
Matrix Switcher Example Inputs Outputs
300 MHz Sweep Example of a real world sweep Critical Areas
Another 300 MHz Sweep But still some loss
Without sweeping the product we don t know Shape of the curve The 0-10 MHz area Critical area for smearing The 0-130 MHz area Area where most of our video information is located
Smearing Review
Dot Clock A term to describe pixel speed How many pixels per second Pixels x Lines x Refresh VESA XGA= 65 MHz Very important in digital signal handling Graphic card performance Digital display sampling Does not compensate/account for the analog nature of most video systems. Loss of power NOT THE SAME AS BANDWIDTH Very similar though
Using Twisted Pair (TP) Wiring in AV Systems Another Solution
What can you do with TP? Traditional Uses Networks Voice transmission What about Analog Video? Requires transmitter and receiver Creates differential video signal Balanced Video Signal
Why use TP for video? Inexpensive, light, already there Ideally suited for: LONG runs (over 300 ) Limited conduit space runs Temporary setups Need to easily remove the transmitter with minimal effort
4 Things to Know when using TP for Analog Video Signal Transmission
1. Do not pass through IT network components There is voltage & other signals that are not data signals Routers & hubs are looking for data signals A good way to blow up a $25,000 router
2. Wire Map Is it wired correctly pin to pin?
2. Wire Map T568A Common in networks that require telephony compatibility T568B Common in straight data networks
3. Delay Skew Propagation difference between pairs Time difference between shortest and longest pair
3. Delay Skew You must compensate for these differences If you don t, you get misconverged images Do one of two things: Discrete delay inside Coax outside to compensate for delay
3. Delay Skew Test to determine the skew Document it Then add the compensatory cables Where to add it? Wherever you can reach it Usually at the far end (Projector)
Compensating for Delay Skew Some products provide a timing delay for each color channel Allows SKEW to be compensated for in an external box with minimal loss. Signal Transmission
Skew-Free A/V UTP Cable Wire pairs are manufactured specially for AV applications Three of the pairs have identical twist ratios No Delay Skew error. The Orange pair twists in the opposite direction To reduce crosstalk Now the 4 pairs are not interchangeable CAN NOT BE USED FOR NETWORK APPLICATIONS
4. Termination Tip If your company is not experienced at making quality termination Terminate JACKS! Don t try to terminate plugs!
Mixing & Matching NO MIXING MANUFACTURER TWISTED PAIR PRODUCTS! Technology is proprietary You may damage equipment
TP Transmission Distance Examples Resolution Video 640 x 480 (VGA) 800 x 600 (SVGA) 1024 x 768 (XGA) 1280 x 1024 (SXGA) 1600 x 1200 (UXGA) Distance 1000 1000 800 600 400 200
TP Products Transmitters & Receivers
TP Transmitters Different transmitter types Desktop Architectural BNC Different needs Different applications
Many Different Receivers TP Receivers Desktop BNC Short range/long range Different needs Different applications
New Approach
Twisted Pair A/V Switching and Transmission System Up to 500 TP Wire (Depending on Resolution) Control S-Video Composite RGBHV Out Amplifier VGA PC Laptop VCR DVD
Twisted Pair Matrix Switcher
Review What are the main factors that affect signal transmission in analog video systems? What are the adjustments that compensate for them? What is the bandwidth rule of thumb? Why is it important? What is one advantage for using TP for video? What is the number one thing we have to remember when using TP wiring for video?
Questions?