Wikipedia:Reference desk/Archives/Computing/2014 December 24

= December 24 =

Bizarre TV interference problem ?
1) My TV has many inputs, including composite (R,G,B) and component (Y,R,W). The same plug is shared between the composite Green cord and the component Yellow cord (which contains the entire video).

2) I use a set-top box to receive broadcast TV stations and pass them on to the TV. The set-top box only has component outputs, so I have plugged in the Yellow, Red, and White cords (Red and White being audio right and left channels).

3) If I set the TV to display using the component inputs, it displays properly. Surprisingly, if I set it to composite inputs, it still displays something, even though it only has the composite video sent to the Green plug, and nothing at all plugged into the Red and Blue plugs.  I get a grey-scale image, with what looks like every other pixel blacked out.

4) Now here's the really weird part. My set top box gets much better reception when the TV is set to composite inputs than component, on the same station. The reception bars go from about 1/3 to 2/3 up.  This is on US RF frequency channel 45, which should help to identify the final frequency.

So, all I can think of is that the TV generates some type of interference when in one mode that it doesn't in the other, which affects the set-top box's ability to receive broadcast TV. Is this possible ? Any other theories ? StuRat (talk) 18:06, 24 December 2014 (UTC)


 * Actually, the red, green, and blue cables are component video. The yellow, red, and white cables are composite video and stereo audio. Component video encodes brightness on the green cable, and color on the red and blue cables; composite video encodes brightness and color on one cable.


 * I think the major difference between composite and component is composite uses a special color signal that is combined with brightness on the cable and then re-extracted into color information by the TV. The composite color signal is 3.58 MHz (see NTSC - Color encoding and Colorburst) and RF channel 45 is from 656 to 662 MHz (see North American television frequencies - Broadcast - UHF band), but I don't know if this suggests interference or not. Maybe something in how the TV decodes the composite color signal is causing interference? --Bavi H (talk) 01:14, 25 December 2014 (UTC)


 * If your prob is not solved, check the following:
 * If your two devices have a interference of power line, connect the chassis' ground by ground or when one of the devices is using a C1, C7 or C9 connector, turn it by 180 degrees frist.
 * Whe using TV color system PAL, SECAM, NTSC, international sold devices support all this and the color freqency shift of 3,58 Mhz or 4,433 Mhz.
 * Only use a 75 Ω electrical impedance coaxial cable for video.
 * -- Hans Haase (有问题吗) 23:24, 27 December 2014 (UTC)


 * Well, I "resolved" the issue by avoiding using the connection type which causes poor reception, since I have the choice of two methods. StuRat (talk) 21:48, 28 December 2014 (UTC)