paul@kuhub.cc.ukans.edu (04/05/91)
X-NEWS: kuhub.cc.ukans.edu rec.video: 14905 Relay-Version: VMS News - V6.0-2 30/01/91 VAX/VMS V5.4; site kuhub.cc.ukans.edu Path: kuhub.cc.ukans.edu!caen!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!att!ucbvax!cleveland.Freenet.Edu!ac365 Newsgroups: rec.video Subject: Setting Clocks Message-ID: <9104021909.AA17060@cwns1.INS.CWRU.Edu> From: ac365@cleveland.Freenet.Edu (Todd Donovan) Date: 2 Apr 91 19:09:30 GMT Reply-To: ac365@cleveland.Freenet.Edu Sender: daemon@ucbvax.BERKELEY.EDU Lines: 34 >Or, better yet: > > Have the television networks send out the time of day in addition > to the signals currently sent out during the vertical blanking > interval. (The current signals include information for fine > tuning the color, and close captioning.) Of course, this will > not help devices that do not have a TV tuner, such as alarm clocks. > I know that NBC already does send out the time of day during the vertical blanking, and I have to believe that the other networks also provide this information. Keep in mind that each part of the country is on a slightly different power frequency and this will cause cummulative errors in clocks. This and the fact that cheaper clocks tend to easily get off, caused NBC to implement a "network clock" so that all affiliates had exactly the same time. Since the human factor in master control of most stations is being eliminated, and automation introduced, there is no one to simply look at network feeds and know what should be on the air. Since the television day is broken down to the second, there is no room for slippage when local stations insert commericals or simply just link-up with the network. Thus the need for over 200 syncronized clocks...updated each second. As of yet, I know of no easy way for the home user to decode these signals and use them for the setting of clocks. -- /| Todd Donovan: ac365@cleveland.freenet.edu / | President and General Manager /__| Channel 4 WCFT-Television Chagrin Falls The Place To Be!, NBC | =======================================================================
Mills@udel.edu (04/06/91)
Todd, Darn, another station heard from. Do we get to send news briefs via SMTP now? Have you a suggested MIB for your station equipment? As a former engineer and combo man for a motley crew of radio and tv stations in and around Ann Arbor and Detroit, things must have changed a lot over the last twenty years. And still the network programs start one second late, which the affiliates try to fill with expanding promos... First, I don't know where NBS gets the time. At the Detriot NBC affilitate (call letters used to be WWJ) the time came down the wire (remeber the bing-bing-bong?) and then the buttons got pushed. [we all studio buzzards were hams, so our intercom was a Morse key and buzzer - worked great]. The reason it was done that way was that the Western Union clock clunkers introduced their time corrections just before or on the hour, which led to a clear violation of the Principle of Least Astonishment. On your comment on mains frequency. For all of the US except Texas and west of the Rockies, the mains are synchronized to the same frequency and phase, as established by a WWVB receiver somewhere in Ohio. Texas has their own system established I am told by reason of oil depletion allowance regulations or some similar silly reason. West of the Rockies frequency control is closed-loop and maintained automatically. On our side the loop is apparently closed only in paw-to-knob mode. I don't know if your reference to frequency implies you genlock to local power, which means you could have up to a frame-jitter (do the even and odd fields have individual timestamps (gawd)?) from true tick. You can, of course, readily detect the timecode using a delayed-sweep display on an oscilloscope, but, while I have not looked in a while, the resolution of the code does not appear to be much better than a second anyway. Having said all this, and aware that all three tv networks have rubidium standard in New York which where once upon a time proposed as a ubiquitous dissemination method for NBS time (genlock and local frame storage killed that idea), independent WTTG in Washington still ticks the atomic second and USNO still publishes their offsets weekly (weakly?). That's in fact very useful if you want nanosecond time and you happen to live within the coverage area. Dave
clements@bbn.com (Bob Clements) (04/08/91)
>I know that NBC already does send out the time of day during the >vertical blanking, and I have to believe that the other networks also >provide this information. Yeah, they do, but that doesn't mean you get it from your local affiliate. The time is not on a line that is normally broadcast, like closed captions are. It's up higher in the vertical interval. Typically, locally generated test signals are placed there by the time it's broadcast. I remember some years ago that channel 5 in Boston had test signals there but channel 9 across the border in New Hampshire transmitted the network time code. (These are both ABC outlets.) None of the Boston stations transmit the time code, so I dropped the idea of building a decoder for it. Bob Clements, K1BC, clements@bbn.com