Video Cables - RF Cables Part 2

Contents

1. Introduction to Video Cables 

2. Characteristics of a 75 Ohm Video Cable 

3. Cable TV (CA TV) 

4. CCTV (Closed Circuit TV) 

5. Video Cables
   i. HD TV 
   ii. Composite Video Cables
   iii. RF Video Cable 
   iv. S Video Cable 
   v. DVI Cables 
   vi. HDMI Cable

6. Video Adapters 

7. Conclusion

8. Annexures
    

1. Introduction to Video Cable types based on their applications: 

Video cables are commercially available cables widely used in video and multimedia applications. A distinction is made between the commercial video cable and a RF cable used in CATV and CCTV industry. This article discusses some of the RF cables used in CATV and commercial video applications.

2. Characteristics of a 75 ohms Video cable

Video signal transmission standard such as HDTV rely on video cables, which have a tight control on their characteristic impedance of 75 ohms. This achieved by a video cable manufacturer by maintaining an uniformity in the dimensions (shield and center conductor) of the cable and the material used in constructing the dielectric insulator, braid shield and the outer jacket. Any variation in its dimension along the length of the cable will change its characteristic impedance, which in turn will impact the video quality. A poor return loss of a video cable degrades the video signal integrity and quality.

A common source of error happens when constructing a solder style RCA connector with a 75-ohm coaxial cable. The error happens due to the way the RCA connector is soldered to the coax, disturbing the spatial relationship between the center conductor and the shield ground. A 75-ohm coaxial cable should use crimping technique to assemble a video cable. It should use a 75-ohm style RCA connector crimped to the coax to retain the equidistant relationship between the center conductor and ground shield.

3. CATV Cable 

Cables can be classified based on the kind of signals they are propagating as each present a set of characteristics specific to it. A high frequency cable meant for analog video channels for example in a CATV distribution network should exhibit low attenuation (and a favourable frequency response) over a broad band of frequency (up to 1 GHz) to support the downstream CATV program TV channels. A single analog video channel is VSB (vestigial side band) modulated signal and has audio and video sub carriers embedded into it. Therefore, the cable being used to transport these signal should offer the right characteristics impedance, radiation free and low attenuation to the signals transmitted from the headend to the subscriber's residence. Any break in the cable or loose connector joint could lead to poor return loss and unsatisfactory performance for the network. RG 6, RG11 and RG59 are popular coaxial cable for CATV applications.

Fig. Typical construction of RG11 cable

In a CATV distribution network, various types of RF cables are used to transport signals from headend to the customer residence. There is feeder coaxial cable, typically 1 inch in diameter, and installed in long runs in rugged environment; the branch cables (0.5 in dia.) and the drop cables. Typical application of RG11 is as drop cable for CATV/MATV, Broadband, HDTV and Satellite Broadcasting and as trunk cable. 

Features of RG11 cable 

• The center conductor is copper covered with steel (known as copper clad steel) and has a diameter of 1.63 mm (0.064 in), equivalent to a wire gauge standard of 14 AWG. 
• There are 4 outer shields constructed over the dielectric. The first one is a bonded aluminium foil shield, followed by aluminium braid shield constructed out of 34 AWG or 0.16 mm aluminium wire. The nominal diameter of the first outer shield is 7.26 mm or 0.280 in. The third shield is an additional aluminium foil followed by the 4th shield, which is again an aluminium braid shield. 
• The dielectric material used is a gas expanded polyethylene 
• Finally, a jacket covers the entire cable structure. The jacket is made of flame retardant PVC and is 0.83 mm thick. The nominal diameter of the jacket is 10.29 mm or 0.405 in. 
• It is a 75 ohms cable 
• Velocity of propagation is 85% nominal 
• Capacitance between the inner conductor and the shield: 53.1 pF/m or 16.2 pF/ft 
• Attenuation of the typical RG11 cable, as given by one of the cable manufacturer (www.hosiwell.com/) is given in Annexure 2. 

4. CCTV (Closed Circuit TV) 

CCTV is another application, like CATV, which relies on effective transmission and distribution of video signal. A CCTV system is a camera-based system, which is connected to a central hub using video cables. It uses a coaxial cable system for video signal distribution, just like CATV system. Although the motive is same in both these applications, there are minor differences in their characteristics and it is not advisable to use a common type of video coaxial cables for both these applications. The difference comes from the fact that, CCTV system transmits and distributes base band composite video, which includes low frequency signal, whereas a CATV system carries signal in the RF range. Hence, the type of coaxial cable and their characteristics are different for each of these systems. 

In view of this difference the following points highlight the requirement of a CCTV cable system compared to that of a CATV: 

• For CCTV application, it is desirable to have bare copper center conductor, whereas for CATV application a copper plated steel center conductor is adequate. This is because bare copper has low DC resistance at low frequency baseband video signals, hence less signal attenuation compared to copper plated steel. Whereas for CATV application, the cable carries high frequency broadband video signal, resulting in confinement of the signal propagation near the surface of the center conductor (due to skin effect). 
• The coaxial cable used for CCTV application has shield made of bare copper braid having a shielding effectiveness of 95% or better, in order to shield the video signal from external electrical interference. Additional aluminium foil is also used for RFI shielding. 
• CCTV cable lengths are smaller compared to CATV cable runs, hence RG59 type is most frequently used for this application. For longer cable runs (of several thousands of feet) RG11 type of cable can be used. 

5. Video Cables

Video cables are categorized depending upon the signals they carry, more appropriately, the formatting of the video signals they support. Video cables can be classified into five different cable transmission options for connecting video devices and video displays. With the advancement of new video transmission standards based on digital modulation of the video signal techniques, newer cables have emerged. One of the important factors in determining the quality of the video cable is its resolution capability. Each of the cables described below also mentions the resolution capability:

1. Composite Video (a single RCA connection) - Capable of SDTV at 480i resolution. 
2. S-Video (a single 4-pin connection) - SDTV at 480i and EDTV at 480p resolution with wide screen display. 
3. Component Video (three RCA or BNC connectors, or a single 15-pin connection) - Capable of SDTV at 480i, EDTV at 480p, HDTV at 720p, 1080i & 1080p. 
4. RGB / RGBHV Video (five BNCs or a single 15-pin connection) - Capable of SDTV at 480i, EDTV at 480p, HDTV at 720p, 1080i & 1080p. 
5. Digital Video such as HDMI, DVI, DFP, M1, EVC and P&D which can all be plugged into each other with the appropriate cable - Capable of SDTV at 480i, EDTV at 480p, HDTV at 720p, 1080i & 1080p.

The first four transmission types listed above are analog video formats. Analogue video is the common form of video transmission as compared to digital video transmission, which have gained popularity in recent times. The quality of video transmission in both the cases depend on the video formatting used, the electrical specification of the cable, connector terminations and the display device, the kind of video compression and error correction techniques used etc. For getting the best quality of video it is important to match the resolution of the video source with the resolution capability of the display device to determine the video cable option. For example when choosing a video cable one should match the highest resolution of the video source offered with the display device. SDTV content on HDTV is a mismatch in the same way as trying to display HDTV content on SDTV display.

In the following sections, we will discuss a few widely used video cables as given below:

i. HDTV 
ii. Composite Video Cables 
iii. RF Video Cable 
iv. S Video Cable 
v. DVI Cable 
vi. HDMI Cables

i HDTV Cables

High-definition television (or HDTV) refers to video with resolution higher than traditional TV systems (standard-definition TV, or SDTV). Early HDTV broadcasting used analog techniques. Today HDTV is broadcast digitally using video compression techniques. HDTV Cables carry HDTV video transmission signals with resolutions of 1280x720 pixels (720p) or 1920x1080 (1080i or 1080p), and HDTV- equivalent resolutions

Fig. Component video cable for HDTV application

1366x768 (WXGA) used between computers and HDTV displays. Component video cables are commonly used for HDTV application. Component video is a video signal that has been split into two or more components. In popular use, it refers to a type of analog video information that is transmitted or stored as three separate signals. Component video refers to analog YPbPr component video with sync on luma.

Component video cable such as Canare V33C high-resolution cable uses impedance-matched connectors and designed to protect HDTV signals from interference. The cable features: 

• Impedance controlled, 75-ohm coaxial cable for accurate signal transfer 
• Impedance-matched 75-ohm crimp style connectors preserve 75-ohm signal accuracy 
• High density copper braid shielding and shielded connectors ensure maximum protection from RF and electro-magnetic interference. 
• Reputed brands of RCA connectors such as Canare's feature 75-ohm crimp style design, shielded barrels and gold-plated contacts for optimal signal transfer 
•   Backward compatible with SDTV and EDTV.

ii. Composite Video Cables

Composite video is an analog TV format for picture signal before it is combined with a sound signal and modulated on an RF carrier. It contains all required video information: such as the colour information combined into a single line. Composite-video cables do not carry audio and are often paired with audio cables. It is a composite of three source signals called Y, U and V (YUV) with sync pulses. Y represents the brightness or luminance of the picture and U, V represent hue and saturation or chrominance respectively.

RCA Cable		BNC Cable

Composite video has standard formats such as NTSC, PAL, and SECAM. RCA connectors are used in general, however professional applications use BNC connectors and higher quality coaxial cables. Composite cable carries composite video signals and are available with different types of connectors such as RCA, F and BNC. 

iii. RF Video Cable

RF video cable such as those used in home theatre and other video centric applications are built to 75-ohm characteristic impedance specification and are impedance matched to the connectors used. For example Canare brand L-4CFB cable features:

Fig. RF video cable 

• These cables are useful for applications such as satellite receivers, VCRs, video displays, DVRs, VCRs, television tuners or other RF devices. 
• Video Signal transmission quality and integrity is maintained 
• Foam PE insulation provides good signal integrity 
• Solder less 75-ohm style connectors are used for signal accuracy 
• Dual shields (high-density copper braid and foil) ensure maximum protection from RF and electro-magnetic interference. 
• Precision-machined interfaces and gold-plated contacts reduce oxidation and ensure optimal signal transmission.

iv. S Video Cable

S video or Separate Video is also called Y/C and is an analog video transmission standard. S-Video carries standard definition video (typically at 480i or 576i resolution), but does not carry audio on the same cable. S video cable such as Belden brand 1808A cable is assembled using low-loss connectors to ensure video quality. Dual 75-ohm coaxial channels, high-density copper braid shielding and metal-shielded connectors are used to ensure signal integrity.

Fig. S video Cable with pin configuration details

The important features of the cable are given below:

• Dual internal 75-ohm coaxial channels for distinct colour and brightness 
• High-density shielding and metal-shielded connectors for signal protection 
• Precision-machined connectors feature gold-plated contacts & pins, polished metal barrels and silver-content solder to ensure jitter-free transmission. 
• Rubberised PVC jacket and strain relief springs prevent cable damage and kinking near the connector.

v. DVI Cables

The high-definition DVI cables are designed to deliver the latest HDTV resolutions using DVI digital transmission or RGB/VGA transmission. DVI cables are useful for video gaming and home theatre applications.

The DVI cable features the following:

• Support for HDTV at 720p, 1080i, 1080p or WXGA widescreen resolutions, or connect PC style VGA/RGB video formats up to WUXGA (1920 x 1200). 
• Backwards compatible to connect SDTV (480i), EDTV (480p) and PC style VGA/RGB video formats up to WUXGA 1920 x 1200 (WUXGA). 
• Heavy duty shielded cable and internally shielded connectors protect signals from electro-magnetic and RF interference. 
• Precision-machined interface and gold-plated pins prevent jitter and ensure optimal signal transfer. 
• Rugged PVC jacket and moulded connectors ensure durability. 
• DVI-I type connections allow digital or VGA/RGB compatibility. 
• Typical Cable Connection is male

vi. HDMI Cable

HDMI is a digital interface standard that supports HDTV type of video transmission standards. It offers backwards compatibility for other video formats. HDMI cables are constructed with heavy-duty external shield and internally shielded connectors. The internally shielded connectors protect sensitive signals from tip to tip. HDMI has a 19-pin connector, the details of which are shown in the figure below: (Please refer to Annexure D for detailed pin configuration)

The precision-machined interfaces and gold-plated pins ensure jitter-free transmission. These cables are useful for video-intensive applications such as video game or home theatre environment. 

The HDMI cable features:

• Supports HDTV at 720p, 1080i or 1080p and PC style video up to WQXGA (2560x1600) 
• Backwards compatible with SDTV (480i), EDTV (480p & widescreen) and all PC VGA style video formats up to WQXGA (2560x1600).
• Heavy duty shielded cable and internally shielded connector casings ensure end-to-end signal protection. 
• Precision-machined interface and gold-plated pins prevent jitter and ensure optimal signal transfer. 
• Supports HDMI 1.3 capabilities which allows the addition of loss less HD audio formats (Dolby TrueHD and DTS-HD Master Audio™) to Dolby® Digital and DTS® formats, and higher bandwidth capability allows increased resolution, colour space and frame rates. 
• Rugged PVC jacket and moulded connectors ensure maximum durability.

Several other popular video cables are listed in annexure C.

6. Video Adapters

Video adapters play a role of transition manager between two similar or two different types of connectors by mating the two. There are different adapters available in the market, which are listed in the Annexure A.

7. Conclusion

Video cables have a wide variety of industry standards, and therefore have that many types of cable and connector configurations. Video cables are the most widely used cables in the industry. In this article we have discussed some of the widely used video cables, but by no means covered all types of video cables. For more information about video cables, readers are suggested to visit websites such as www.hdmi.org, www.dvi.com, www.mpeg.org, and many others 

8. Annexures

Annexure A:

VGA to Component Video Adapter, Component Video Adapter - 15-Pin Female / 3-RCA Male, Component Video Adapter - 3-RCA Female / 15-Pin Male, 15-Pin Male to 5-BNC Female,

Fig. Some commonly used video adapters

Component to DVI Video Adapter (DVI Male to 3-RCA-F), 
HDMI Female to DVI Male, 
DVI to 15-Pin VGA Adapter, 
DVI Male to 15-Pin Female, 
S-Video Male to BNC Female, 
S-Video Male to RCA Female (Composite Video to S-Video), 
4-Pin Male to (2) 4-Pin Female (S-Video Splitter), 
Component or VGA to DVI Converter, 
4-Pin Female to 4-Pin Female (S-Video Coupler), 
F Male/Female to RCA Male/Female, 
F Male/Female to BNC Male/Female, 
BNC Male/Female to RCA Male/Female, 
15-Pin to RCA to 4-Pin S-Video (PC/Mac to TV Adapter), 
15-Pin Male/Female to 9-Pin Female/Male (EGA/CGA/Monochrome Monitor Adapter), 
4-Pin Male to (2) RCA Male (S-Video to Brightness & Colour), 
4-Pin Male to (2) BNC Female (S-Video to Brightness & Colour), 
DVI Y Cable - DVI to 15-Pin & DVI

Annexure B:

Fig. Attenuation chart for RG11 cable (Manufactured by Hosiwell)

Annexure C:

• 15-Pin Video Cables (VGA Cables) 
• Component Video Cables
• Component to DVI Cables 
• Component to VGA Cables 
• DVI to HDMI Video Cables
• DVI to BNC Video Cables 
• Digital Video Cables (DVI, HDMI, M1, DFP) 
• RGB Video Cables (RGB & RGBHV) 
• Component Video Cables: 15-Pin / 3-RCA or 3-BNC 
• 15-Pin to 5-Connectors Video Cables (RGBHV) 
• S-Video to RCA Cables " HDMI to 15-Pin VGA Cables 
• DVI to 15-Pin Video Cables 
• 4-Channel RGBS Video Cables 
• 5-Channel RGBHV Video Cables
  
  

Annexure D:

Fig. HDMI Cable (Courtesy: hdmi.org)

Pins 1 through 9 carry the three TMDS data channels (Transition Minimized Differential Signaling - the technology that allows DVI and HDMI to send high-speed digital data), three pins per channel. TMDS data includes both video and audio information, and each channel has three separate lines for + values, - values, and a ground or data shield. 

Pins 10 through 12 carry data for the TMDS clock channel, which helps keep the signals in synchronization. As with the TMDS data channels, there are separate lines for + values, - values, and a data shield. 

Pin 13 is carries the CEC (Consumer Electronics Control) channel, used for sending command and control data between connected devices. 

Pin 14 is reserved for future use. 

Pins 15 and 16 are dedicated to the DDC (Display Data Channel), used for communicating EDID (Extended Display Identification Channel) information between devices. 

Pin 17 is a data shield for the CEC and DDC channels. 

Pin 18 carries a low-voltage (+5V) power supply. 

Pin 19 is the Hot Plug Detect, dedicated to monitoring power up/down and plug/unplug events.