barryg@sdcrdcf.UUCP (Lee Gold) (03/12/85)
We have a cable hook up with two boxes, one for the VCR and one for the TV. And a switch that selects whether the TV shows the TV Cable box, or the VCR signal (which in turn may be either the VCR Cable box -- or the VCR output, depending on whether the VCR is switched to TV or VCR). VCR output can either be the VCR's demodulation of the Cable signal, its tuning of a regular station (if I've switched its input from Cable box to antenna), or a VCR tape. The TV receives the Cable fine. The VCR sends the Cable directly fine (when switched onto TV) The VCR broadcasts tapes fine. The VCR broadcasts antenna signals fine. BUT...sometimes when the VCR taping/rebroadcasting a Cable signal (when switched onto VCR), there's a loathsome hissing noise. The better the picture, the worse the noise. Turning off the TV and VCR AFC switches helps a little. The noise is most intense on the VCR's bulletin board channel with lettering...or when there are subtitles. What can be causing this? Any suggestions for what to do about it? Thanks in advance. --Lee Gold
lauren@vortex.UUCP (Lauren Weinstein) (03/13/85)
Two points: 1) Many VCR tuners do not have adequate filtering to directly demodulate cable signals without adjacent channel interference problems. You need to feed through a cable converter in such cases. 2) The loud hissing (buzzing) noise on subtitles, information channels, etc. indicates that the signal input level is too high into the VCR tuner, and that as a consequence the video is bleeding over into the audio subcarrier (simplified explanation). Sometimes slight detuning will help, with some loss of video quality. RF attenuators may also be useful to cut down on overly strong signals in some cases. --Lauren--