gjw@clyde.UUCP (Gregory J. Wroclawski) (02/13/85)
The recent discussion about monitors and TV sets had a couple of minor errors about resolution and bandwidth (BW) in the NTSC (National Television Standards Comittee) system. The luminace BW in NTSC is 4.2 MHz and until the advent of comb filters was severely limited past 3.0MHz in TV's due to the color burst trap needed at 3.58 MHz. This limited the horizontal resolution to the equivalent of ~260-270 lines. I believe all Monitor/Receiver TV's have comb filters these days to be able utilize the full 4.2 MHz of transmitted luminace info. This gives the full 350 lines of horizontal resolution advertised by many manufactures. Any more resolution is superfluous since the it would only be usable through the seperate composite video inputs that many of the Monitor TV's have. The color information in composite video is carried by two color chrominace signals called the I and Q vectors. The I chrominace signal is VSB (vestigle sideband) modulated onto the 3.58 MHz color carrier with 1.5 MHz of bandwidth and the Q chrominace signal is DSB modulated onto the 3.58 MHz color carrier with 500KHz of bandwith. All TV's whether they are Monitor/TV's or regular TV's demodulated only 500 KHz of the transmited 1.5 MHz of the I chrominace signal. This is limited by the chrominace processor so it is limited even if one uses the composite video input. Since, I recently was in the market for a TV I found that the only TV that fully demodulates the full I chrominance bandwidth was the new RCA Colortrack 2000 series with the CTC-131 chassis. This was due to the new color signal processor chip designed by RCA and used exculsively in their TV's. You can look it up in the Nov 84 issue of IEEE transactions on Consumer Electronics. This TV also has RGB inputs with a claimed bandwidth of 6MHz. Although not speced in the owners manual the composite video inputs according to a test in the Jan 85 issue of Modern Electronics have a luminace bandwidth of 8 MHz. VCR's due to technology limitations at the time they developed the 1/2" format limit the luminance bandwith to about 3.0 MHz. This was probably done since all color TV's at the time limited the luminace BW to the same point. This is quite apparent to me since I had bought the new Monitor/TV. A show I am watching and taping at the same time is much clearer and sharper when watching it in real time(i.e of the air) than when played back through the VCR. This difference was not noticeable with my old color TV. I read that the Japanese are developing a VHS compatible VCR that would be compatible with the existing VHS tapes but would provide 400 lines of luminace bandwidth.